RESUMO
Premelanosome protein (PMEL), a melanocyte-specific glycoprotein, has an essential role in melanosome maturation, assembling amyloid fibrils for melanin deposition. PMEL undergoes several post-translational modifications, including N- and O-glycosylations, which are associated with proper melanosome development. C-mannosylation is a rare type of protein glycosylation at a tryptophan residue that might regulate the secretion and localization of proteins. PMEL has one putative C-mannosylation site in its core amyloid fragment (CAF); however, there is no report focusing on C-mannosylation of PMEL. To investigate this, we expressed recombinant PMEL in SK-MEL-28 human melanoma cells and purified the protein. Mass spectrometry analyses demonstrated that human PMEL is C-mannosylated at multiple tryptophan residues in its CAF and N-terminal fragment (NTF). In addition to the W153 or W156 residue (CAF), which lies in the consensus sequence for C-mannosylation, the W104 residue (NTF) was C-mannosylated without the consensus sequence. To determine the effects of the modifications, we deleted the PMEL gene by using CRISPR/Cas9 technology and re-expressed wild-type or C-mannosylation-defective mutants of PMEL, in which the C-mannosylated tryptophan was replaced with a phenylalanine residue (WF mutation), in SK-MEL-28 cells. Importantly, fibril-containing melanosomes were significantly decreased in W104F mutant PMEL-re-expressing cells compared with wild-type PMEL, observed using transmission electron microscopy. Furthermore, western blot and immunofluorescence analysis suggested that the W104F mutation may cause mild endoplasmic reticulumretention, possibly associated with early misfolding, and lysosomal misaggregation, thus reducing functional fibril formation. Our results demonstrate that C-mannosylation of PMEL is required for proper melanosome development by regulating PMEL-derived fibril formation.
Assuntos
Amiloide , Triptofano , Humanos , Glicosilação , Triptofano/genética , Triptofano/metabolismo , Amiloide/química , Melanossomas/genética , Melanossomas/metabolismo , Glicoproteínas/genética , Glicoproteínas/metabolismo , Proteínas Amiloidogênicas/metabolismo , Antígeno gp100 de Melanoma/genética , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/metabolismoRESUMO
Vitiligo is an autoimmune skin disease, characterized by depigmentation and epidermal melanocytes loss. The specific mechanisms underlying vitiligo have not been fully understood. As a result, treating vitiligo is a dermatological challenge. Recently, much attention has been paid to the dysfunction and interaction of organelles under environmental stress. The impaired organelles could generate misfolded proteins, particularly accumulated toxic premelanosome protein (PMEL) amyloid oligomers, activating the autoimmune system and cause melanocyte damage. Unfolded protein response (UPR) dysfunction accelerates toxic PMEL accumulation. Herein, we presented a narrative review on UPR's role in vitiligo, the misfolded PMEL-induced attack of the autoimmune system under autophagy dysfunction caused by abnormal activation of transient receptor potential (TRP) channels and the background of UPR system defects in melanocytes. All of these mechanisms were integrated to form UPR/PMEL-TRP channels/autophagy axis, providing a new understanding of vitiligo pathogenesis.
Assuntos
Apoptose , Autofagia , Melanócitos/metabolismo , Melanossomas/metabolismo , Canais de Potencial de Receptor Transitório/metabolismo , Vitiligo/metabolismo , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/metabolismo , Animais , Humanos , Melanócitos/patologia , Melanossomas/patologia , Conformação Proteica , Desdobramento de Proteína , Transdução de Sinais , Pigmentação da Pele , Relação Estrutura-Atividade , Vitiligo/patologiaRESUMO
The pre-melanosomal protein (Pmel17) is a human functional amyloid that supports melanin biosynthesis within melanocytes. This occurs in the melanosome, a membrane-bound organelle with an acidic intraluminal pH. The repeat region of Pmel17 (RPT, residues 315-444) has been previously shown to form amyloid aggregates under acidic melanosomal conditions, but not under neutral cytosolic conditions, when expressed and purified using a C-terminal hexa-histidine tag (RPT-His). Given the importance of protonation states in RPT-His aggregation, we questioned whether the histidine tag influenced the pH-dependent behavior. In this report, we generated a tagless RPT by inserting a tobacco etch virus (TEV) protease recognition sequence (ENLYGQ(G/S)) immediately upstream of a native glycine residue at position 312 in Pmel17. After purification of the fusion construct using a histidine tag, cleavage with TEV protease generated a fully native RPT (nRPT) spanning resides 312-444. We characterized the aggregation of nRPT, which formed amyloid fibrils under acidic conditions (pH ≤ 6) but not at neutral pH. Characterizing the morphologies of nRPT aggregates using transmission electron microscopy revealed a pH-dependent maturation from short, curved structures at pH 4 to paired, rod-like fibrils at pH 6. This was accompanied by a secondary structural transition from mixed random coil/ß-sheet at pH 4 to canonical ß-sheet at pH 6. We also show that pre-formed nRPT fibrils undergo disaggregation upon dilution into pH 7 buffer. More broadly, this strategy can be utilized to generate native amyloidogenic domains from larger proteins by utilizing intrinsic N-terminal glycine or serine residues.
Assuntos
Amiloide/química , Melanossomas/metabolismo , Antígeno gp100 de Melanoma/química , Sequência de Aminoácidos , Endopeptidases/química , Corantes Fluorescentes/química , Glicina/química , Histidina/química , Humanos , Concentração de Íons de Hidrogênio , Agregados Proteicos , Serina/química , Espectrometria de Massas em Tandem , Antígeno gp100 de Melanoma/genéticaRESUMO
The pigment cell-specific protein PMEL forms a functional amyloid matrix in melanosomes onto which the pigment melanin is deposited. The amyloid core consists of a short proteolytic fragment, which we have termed the core-amyloid fragment (CAF) and perhaps additional parts of the protein, such as the PKD domain. A highly O-glycosylated repeat (RPT) domain also derived from PMEL proteolysis associates with the amyloid and is necessary to establish the sheet-like morphology of the assemblies. Excluded from the aggregate is the regulatory N-terminus, which nevertheless must be linked in cis to the CAF in order to drive amyloid formation. The domain is then likely cleaved away immediately before, during, or immediately after the incorporation of a new CAF subunit into the nascent amyloid. We had previously identified a 21 amino acid long region, which mediates the regulatory activity of the N-terminus towards the CAF. However, many mutations in the respective segment caused misfolding and/or blocked PMEL export from the endoplasmic reticulum, leaving their phenotype hard to interpret. Here, we employ a saturating mutagenesis approach targeting the motif at single amino acid resolution. Our results confirm the critical nature of the PMEL N-terminal region and identify several residues essential for PMEL amyloidogenesis.
Assuntos
Aminoácidos/química , Domínios Proteicos , Antígeno gp100 de Melanoma/química , Sequência de Aminoácidos , Retículo Endoplasmático/metabolismo , Humanos , Melanossomas/metabolismo , Mutação , Dobramento de Proteína , Transporte Proteico , Frações Subcelulares/metabolismo , Antígeno gp100 de Melanoma/metabolismoRESUMO
Melanoma is a type of skin cancer with increasing incidence worldwide and high lethality. Conventional forms of treatment are not effective in advanced cancer stages. Hence, immunotherapeutic approaches have been tested to modulate immune response against tumor cells. Some vaccine models using tumor-associated antigens (TAAs) such as glycoprotein 100 (gp100) have been studied, but their expected effectiveness has not been shown until now. Antigen immunogenicity is a crucial point to improve the immune response, and therefore mutations are inserted in peptide sequences. It is possible to understand the interactions which occur between peptides and immune system molecules through computer simulation, and this is essential in order to guide efficient vaccine models. In this work, we have calculated the interaction binding energies of crystallographic data based on modified gp100 peptides and HLA-A*0201 using density functional theory (DFT) and the molecular fractionation with conjugated caps (MFCC) approach. Our results show the most relevant residue-residue interactions, the impact of three mutations in their binding sites, and the main HLA-A*0201 amino acids for peptide-HLA binding.
Assuntos
Antígeno HLA-A2/metabolismo , Antígeno gp100 de Melanoma/metabolismo , Simulação por Computador , Teoria da Densidade Funcional , Antígeno HLA-A2/química , Humanos , Modelos Químicos , Mutação , Fragmentos de Peptídeos , Ligação Proteica , Termodinâmica , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/genéticaRESUMO
An epidemiological connection exists between Parkinson's disease (PD) and melanoma. α-Synuclein (α-syn), the hallmark pathological amyloid observed in PD, is also elevated in melanoma, where its expression is inversely correlated with melanin content. We present a hypothesis that there is an amyloid link between α-syn and Pmel17 (premelanosomal protein), a functional amyloid that promotes melanogenesis. Using SK-MEL 28 human melanoma cells, we show that endogenous α-syn is present in melanosomes, the organelle where melanin polymerization occurs. Using in vitro cross-seeding experiments, we show that α-syn fibrils stimulate the aggregation of a Pmel17 fragment constituting the repeat domain (RPT), an amyloidogenic domain essential for fibril formation in melanosomes. The cross-seeded fibrils exhibited α-syn-like ultrastructural features that could be faithfully propagated over multiple generations. This cross-seeding was unidirectional, as RPT fibrils did not influence α-syn aggregation. These results support our hypothesis that α-syn, a pathogenic amyloid, modulates Pmel17 aggregation in the melanosome, defining a molecular link between PD and melanoma.
Assuntos
Melanoma/metabolismo , Doença de Parkinson/metabolismo , alfa-Sinucleína/metabolismo , Antígeno gp100 de Melanoma/metabolismo , Linhagem Celular Tumoral , Humanos , Melanoma/genética , Melanossomas/química , Melanossomas/genética , Melanossomas/metabolismo , Doença de Parkinson/genética , Agregados Proteicos , Domínios Proteicos , alfa-Sinucleína/química , alfa-Sinucleína/genética , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/genéticaRESUMO
The premelanosomal protein (PMEL17) forms functional amyloid fibrils involved in melanin biosynthesis. Multiple PMEL17 isoforms are produced, two of which arise from excision of a cryptic intron within the amyloid-forming repeat (RPT) domain, leading to long (lRPT) and short (sRPT) isoforms with 10 and 7 imperfect repeats, respectively. Both lRPT and sRPT isoforms undergo similar pH-dependent mechanisms of amyloid formation and fibril dissolution. Here, using human PMEL17, we tested the hypothesis that the minor, but more aggregation-prone, sRPT facilitates amyloid formation of lRPT. We observed that cross-seeding by sRPT fibrils accelerates the rate of lRPT aggregation, resulting in propagation of an sRPT-like twisted fibril morphology, unlike the rodlike structure that lRPT normally adopts. This templating was specific, as the reversed reaction inhibited sRPT fibril formation. Despite displaying ultrastructural differences, self- and cross-seeded lRPT fibrils had a similar ß-sheet structured core, revealed by Raman spectroscopy, limited-proteolysis, and fibril disaggregation experiments, suggesting the fibril twist is modulated by N-terminal residues outside the amyloid core. Interestingly, bioinformatics analysis of PMEL17 homologs from other mammals uncovered that long and short RPT isoforms are conserved among members of this phylogenetic group. Collectively, our results indicate that the short isoform of RPT serves as a "nucleator" of PMEL17 functional amyloid formation, mirroring how bacterial functional amyloids assemble during biofilm formation. Whereas bacteria regulate amyloid assembly by using individual genes within the same operon, we propose that the modulation of functional amyloid formation in higher organisms can be accomplished through alternative splicing.
Assuntos
Processamento Alternativo , Amiloide/química , Agregados Proteicos , Antígeno gp100 de Melanoma/química , Amiloide/genética , Amiloide/metabolismo , Humanos , Isoformas de Proteínas , Estrutura Secundária de Proteína , Antígeno gp100 de Melanoma/genética , Antígeno gp100 de Melanoma/metabolismoRESUMO
PMEL is a pigment cell-specific protein that forms a functional amyloid matrix in melanosomes. The matrix consists of well-separated fibrillar sheets on which the pigment melanin is deposited. Using electron tomography, we demonstrate that this sheet architecture is governed by the PMEL repeat (RPT) domain, which associates with the amyloid as an accessory proteolytic fragment. Thus, the RPT domain is dispensable for amyloid formation as such but shapes the morphology of the matrix, probably in order to maximize the surface area available for pigment adsorption. Although the primary amino acid sequence of the RPT domain differs vastly among various vertebrates, we show that it is a functionally conserved, interchangeable module. RPT domains of all species are predicted to be very highly O-glycosylated, which is likely the common defining feature of this domain. O-glycosylation is indeed essential for RPT domain function and the establishment of the PMEL sheet architecture. Thus, O-glycosylation, not amino acid sequence, appears to be the major factor governing the characteristic PMEL amyloid morphology.
Assuntos
Proteínas Amiloidogênicas/química , Melanossomas/metabolismo , Domínios Proteicos , Antígeno gp100 de Melanoma/química , Animais , Linhagem Celular Tumoral , Galinhas , Colubridae , Glicosilação , Humanos , Camundongos , Polissacarídeos/química , Xenopus laevis , Peixe-ZebraRESUMO
The pre-melanosomal protein (Pmel17) aggregates within melanosomes to form functional amyloid fibrils that facilitate melanin polymerization. The repeat domain (RPT) of Pmel17 fibrillates under strict acidic melanosomal pH. Alternative splicing results in a shortened repeat domain (sRPT), which also forms amyloid fibrils. Here, we explored the effects of pH and protein concentration on sRPT aggregation by monitoring the intrinsic fluorescence of the sole tryptophan at position 381 (381W). 381W emission properties revealed changes of local environment polarity for sRPT fibrils formed at different pH. At pHâ¯4, fibrils formed rapidly with no lag phase. A high 381W intensity was observed with a slight blue shift (10â¯nm). These fibrils underwent further structural rearrangements at intermediate pH (5-6), mirroring that of melanosome maturation, which initiates at pHâ¯4 and increases to near neutral pH. In contrast, typical sigmoidal kinetics were observed at pHâ¯6 with slower rates and 381W exhibited quenched emission. Interestingly, biphasic kinetics were observed at pHâ¯5 in a protein concentration-dependent manner. A large 381W blue shift (23â¯nm) was measured, indicating a more hydrophobic environment for fibrils made at pHâ¯5. Consistent with 381W fluorescence, Raman spectroscopy revealed molecular level perturbations in sRPT fibrils that were not evident from circular dichroism, transmission electron microscopy, or limited proteolysis analysis. Finally, sRPT fibrils did not form at pH ≥7 and preformed fibrils rapidly disaggregated under these solution conditions. Collectively, this work yields mechanistic insights into pH-dependent sRPT aggregation in the context of melanosome maturation.
Assuntos
Fluorescência , Agregados Proteicos , Antígeno gp100 de Melanoma/química , Humanos , Concentração de Íons de Hidrogênio , Domínios Proteicos , Isoformas de Proteínas/química , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Triptofano/química , Triptofano/genética , Triptofano/metabolismo , Antígeno gp100 de Melanoma/genética , Antígeno gp100 de Melanoma/metabolismoRESUMO
Lipids often play an important role in the initial steps of fibrillation. The melanosomal protein Pmel17 forms amyloid in vivo and contains a highly amyloidogenic Repeat domain (RPT), important for melanin biosynthesis. RPT fibrillation is influenced by two lysolipids, the anionic lysophosphatidylglycerol (LPG) and zwitterionic lysophosphatidylcholine (LPC), both present in vivo at elevated concentrations in melanosomes, organelles in which Pmel17 aggregate. Here we investigate the interaction of RPT with both LPG and LPC using small-angle X-ray scattering (SAXS), isothermal titration calorimetry (ITC), electron microscopy, fluorescence and circular dichroism (CD) spectroscopy. Under non-shaking conditions, both lipids promote fibrillation but this is driven by different interactions with RPT. Each RPT binds >40 LPG molecules but only weak interactions are seen with LPC. Above LPG's criticial micelle concentration (cmc), LPG and RPT form connected micelles where RPT binds to the surface as beads on a string with core-shell structures. Binding to LPG only induces α-helical structure well above the cmc, while LPC has no measurable effect on the protein structure. While low (but still super-cmc) concentrations of LPG strongly promote aggregation, at higher LPG concentrations (10â¯mM), only ~ one RPT binds per micelle, inhibiting amyloid formation. ITC and SAXS reveal some interactions between the zwitterionic lipid LPC and RPT below the cmc but little above the cmc. Nevertheless, LPC only promotes aggregation above the cmc and this process is not inhibited by high LPC concentrations, suggesting that monomers and micelles cooperate to influence amyloid formation.
Assuntos
Amiloide/química , Lisofosfatidilcolinas/química , Lisofosfolipídeos/química , Antígeno gp100 de Melanoma/química , Agregação Patológica de Proteínas , Domínios ProteicosRESUMO
Genetically inheritable pigmentation defects provide a unique opportunity to reveal the function of proteins contributing to melanogenesis. Dyschromatosis universalis hereditaria (DUH) is a rare pigmentary genodermatosis associated with mutations in the ABCB6 gene. Here we use optical and electron microscopy imaging combined with biochemical tools to investigate the localization and function of ABCB6 in pigment cells. We show that ABCB6 localizes to the membrane of early melanosomes and lysosomes of the human melanocytic cell line MNT-1. Depletion of ABCB6 by siRNA impaired PMEL amyloidogenesis in early melanosomes and induced aberrant accumulation of multilamellar aggregates in pigmented melanosomes. PMEL fibril formation and normal maturation of pigmented melanosomes could be restored by the overexpression of wild-type ABCB6 but not by variants containing an inactivating catalytic mutation (K629M) or the G579E DUH mutation. In line with the impairment of PMEL matrix formation in the absence of ABCB6, morphological analysis of the retinal pigment epithelium of ABCB6 knockout mice revealed a significant decrease of melanosome numbers. Our study extends the localization of ABCB6 to melanosomes, suggesting a potential link between the function of ABCB6 and the etiology of DUH to amyloid formation in pigment cells.
Assuntos
Transportadores de Cassetes de Ligação de ATP/química , Transportadores de Cassetes de Ligação de ATP/metabolismo , Amiloide/química , Amiloide/metabolismo , Melanossomas/metabolismo , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Animais , Linhagem Celular , Imunofluorescência , Humanos , Imuno-Histoquímica , Melanócitos/metabolismo , Camundongos , Camundongos Knockout , Transporte Proteico , Interferência de RNA , RNA Interferente PequenoRESUMO
One of the current challenges facing biomedical researchers is the need to develop new approaches in preventing amyloid formation that is associated with disease. While amyloid is generally considered detrimental to the cell, examples of amyloids that maintain a benign nature and serve a specific function exist. Here, we review our work on the repeat domain (RPT) of the functional amyloid Pmel17. Specifically, the RPT domain contributes in generating amyloid fibrils in melanosomes upon which melanin biosynthesis occurs. Amyloid formation of RPT was shown to be pH sensitive, aggregating only under acidic conditions associated with melanosomal pH. Furthermore, preformed fibrils rapidly dissolved at neutral pH to generate benign monomeric species. From a biological perspective, this unique reversible aggregation/disaggregation is a safeguard against an event of releasing RPT fibrils in the cytosol, resulting in rapid fibril unfolding and circumventing cytotoxicity. Understanding how melanosomes preserve a safe environment will address vital questions that remain unanswered with pathological amyloids.
Assuntos
Amiloide/metabolismo , Domínios Proteicos , Domínios e Motivos de Interação entre Proteínas , Sequências Repetitivas de Ácido Nucleico , Antígeno gp100 de Melanoma/metabolismo , Sequência de Aminoácidos , Amiloide/química , Proteínas Amiloidogênicas/química , Proteínas Amiloidogênicas/metabolismo , Amiloidose , Humanos , Concentração de Íons de Hidrogênio , Melaninas/química , Melaninas/metabolismo , Lipídeos de Membrana/química , Lipídeos de Membrana/metabolismo , Conformação Proteica em Folha beta , Relação Estrutura-Atividade , Antígeno gp100 de Melanoma/químicaRESUMO
Immunotherapies have led to the successful development of novel therapies for cancer. However, there is increasing concern regarding the adverse effects caused by non-tumor-specific immune responses. Here, we report an effective strategy to generate high-avidity tumor-antigen-specific CTLs, using Cas9/single-guide RNA (sgRNA) ribonucleoprotein (RNP) delivery. As a proof-of-principle demonstration, we selected the gp100 melanoma-associated tumor antigen, and cloned the gp100-specific high-avidity TCR from gp100-immunized mice. To enable rapid structural dissection of the TCR, we developed a 3D protein structure modeling system for the TCR/antigen-major histocompatibility complex (pMHC) interaction. Combining these technologies, we efficiently generated gp100-specific PD-1(-) CD8+ T cells, and demonstrated that the genetically engineered CD8+ T cells have high avidity against melanoma cells both in vitro and in vivo. Our methodology offers computational prediction of the TCR response, and enables efficient generation of tumor antigen-specific CD8+ T cells that can neutralize tumor-induced immune suppression leading to a potentially powerful cancer therapeutic.
Assuntos
Antígenos de Neoplasias/imunologia , Linfócitos T CD8-Positivos/imunologia , Linfócitos T CD8-Positivos/metabolismo , Sistemas CRISPR-Cas , Edição de Genes , Neoplasias/genética , Neoplasias/imunologia , Especificidade do Receptor de Antígeno de Linfócitos T/imunologia , Animais , Antígenos de Neoplasias/química , Linhagem Celular Tumoral , Feminino , Técnicas de Inativação de Genes , Genes Reporter , Melanoma Experimental , Camundongos , Modelos Moleculares , Complexos Multiproteicos , Neoplasias/metabolismo , Peptídeos/química , Peptídeos/imunologia , Peptídeos/metabolismo , Ligação Proteica , Conformação Proteica , Multimerização Proteica , Receptores de Antígenos de Linfócitos T/química , Receptores de Antígenos de Linfócitos T/genética , Receptores de Antígenos de Linfócitos T/metabolismo , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/imunologia , Antígeno gp100 de Melanoma/metabolismoRESUMO
PMEL is a pigment cell protein that forms physiological amyloid in melanosomes. Many amyloids and/or their oligomeric precursors are toxic, causing or contributing to severe, incurable diseases including Alzheimer's and prion diseases. Striking similarities in intracellular formation pathways between PMEL and various pathological amyloids including Aß and PrPSc suggest PMEL is an excellent model system to study endocytic amyloid. Learning how PMEL fibrils assemble without apparent toxicity may help developing novel therapies for amyloid diseases. Here we identify the critical PMEL domain that forms the melanosomal amyloid core (CAF). An unbiased alanine-scanning screen covering the entire region combined with quantitative electron microscopy analysis of the full set of mutants uncovers numerous essential residues. Many of these rely on aromaticity for function suggesting a role for π-stacking in melanosomal amyloid assembly. Various mutants are defective in amyloid nucleation. This extensive data set informs the first structural model of the CAF and provides insights into how the melanosomal amyloid core forms.
Assuntos
Proteínas Amiloidogênicas/metabolismo , Melanossomas/metabolismo , Antígeno gp100 de Melanoma/metabolismo , Proteínas Amiloidogênicas/química , Linhagem Celular , Humanos , Antígeno gp100 de Melanoma/químicaRESUMO
In contrast to pathological amyloids, functional amyloids are involved in crucial physiological functions. For instance, the melanosomal protein comprising a highly amyloidogenic polypeptide repeat domain assembles into amyloid fibrils that act as templates for melanin biosynthesis within acidic melanosomes. However, the mechanism-morphology-function relationship of functional amyloids is poorly understood. Here, we demonstrate that the repeat domain of the melanosomal protein exhibits two distinct types of aggregation pathways that display nanoscale polymorphism in acidic pH. In the pH range of 4.5-6, aggregation proceeds via a typical nucleation-dependent mechanism, resulting in the formation of highly ordered ß-rich curvy thread-like fibrils. On the contrary, at pH < 4.5, aggregation occurs through a rapid nucleation-independent isodesmic polymerization process that yields dendritic aggregates having lower degree of internal packing. These dendritic nanostructures can be converted into more stable fibrils by switching the pH. The nanoscale polymorphism associated with the mechanistic switch is likely to be mediated by the altered conformational propensities and intermolecular interactions due to the protonation/deprotonation of critical glutamate residues. We propose that this striking shift in the mechanism that dictates the nanoscale morphology regulates the melanosomal maturation.
Assuntos
Amiloide/química , Proteínas Amiloidogênicas/química , Nanoestruturas/química , Antígeno gp100 de Melanoma/química , Concentração de Íons de Hidrogênio , Cinética , Multimerização ProteicaRESUMO
Generalized vitiligo is an autoimmune disease characterized by melanocyte loss, which results in patchy depigmentation of skin and hair. Recent studies suggested the key role of CD8+T lymphocytes for mediating immune response in vitiligo through melanocyte differentiation antigens, including tyrosinase, gp100 and MelanA/Mart-1. However, the specific epitopes of these auto-antigens are still unknown. In our study, we predicted the possible HLA-A*0201-restricted nonapeptides overlaying the full-length amino acid sequences of these three known antigens and investigated the lymphocytes reactivity to these nonapeptides by Elispot assay. In addition, we evaluated the abilities of these nonapeptides to activate CD8+T cells. We screened out 5 possible epitopes originated from tyrosinase and gp100, numbered P28, P41, P112, P118 and P119. Among these 5 epitopes, notably, P28 and P119 played the dominant role in activating CTLs, with a significant increase in proliferation rate and Interferon-γ (IFN-γ) production of CD8+T cells. Nevertheless, antigen-specific T cell reactivity was not detected in MelanA/Mart-1 peptides. Our studies identified two novel epitopes originated from proteins of gp100 and tyrosinase, which may have implications for the development of immunotherapies for vitiligo.
Assuntos
Autoantígenos/química , Epitopos/genética , Antígeno HLA-A2/genética , Linfócitos T Citotóxicos/imunologia , Vitiligo/genética , Adolescente , Adulto , Sequência de Aminoácidos , Linfócitos T CD8-Positivos/imunologia , Proliferação de Células , Criança , China , Epitopos/imunologia , Feminino , Humanos , Interferon gama/metabolismo , Antígeno MART-1/química , Masculino , Pessoa de Meia-Idade , Monofenol Mono-Oxigenase/química , Vitiligo/imunologia , Adulto Jovem , Antígeno gp100 de Melanoma/químicaRESUMO
Proteasome-catalyzed peptide splicing represents an additional catalytic activity of proteasomes contributing to the pool of MHC-class I-presented epitopes. We here biochemically and functionally characterized a new melanoma gp100 derived spliced epitope. We demonstrate that the gp100(mel)47-52/40-42 antigenic peptide is generated in vitro and in cellulo by a not yet described proteasomal condensation reaction. gp100(mel)47-52/40-42 generation is enhanced in the presence of the ß5i/LMP7 proteasome-subunit and elicits a peptide-specific CD8(+) T cell response. Importantly, we demonstrate that different gp100(mel)-derived spliced epitopes are generated and presented to CD8(+) T cells with efficacies comparable to non-spliced canonical tumor epitopes and that gp100(mel)-derived spliced epitopes trigger activation of CD8(+) T cells found in peripheral blood of half of the melanoma patients tested. Our data suggest that both transpeptidation and condensation reactions contribute to the frequent generation of spliced epitopes also in vivo and that their immune relevance may be comparable to non-spliced epitopes.
Assuntos
Processamento Alternativo , Epitopos/química , Complexo de Endopeptidases do Proteassoma/metabolismo , Antígeno gp100 de Melanoma/química , Algoritmos , Apresentação de Antígeno/imunologia , Antígenos/química , Antígenos de Neoplasias/imunologia , Linfócitos T CD8-Positivos/citologia , Estudos de Casos e Controles , Catálise , Linhagem Celular Tumoral , Epitopos de Linfócito T/imunologia , Células HeLa , Humanos , Interferon gama/metabolismo , Melanócitos/citologia , Melanoma/metabolismo , Peptídeos/química , Probabilidade , Complexo de Endopeptidases do Proteassoma/químicaRESUMO
Human CD8(+) cytotoxic T lymphocytes can mediate tumor regression in melanoma through the specific recognition of HLA-restricted peptides. Because of the relatively weak affinity of most anti-cancer T-cell receptors (TCRs), there is growing emphasis on immunizing melanoma patients with altered peptide ligands in order to induce strong anti-tumor immunity capable of breaking tolerance toward these self-antigens. However, previous studies have shown that these immunogenic designer peptides are not always effective. The melanocyte differentiation protein, glycoprotein 100 (gp100), encodes a naturally processed epitope that is an attractive target for melanoma immunotherapies, in particular peptide-based vaccines. Previous studies have shown that substitutions at peptide residue Glu(3) have a broad negative impact on polyclonal T-cell responses. Here, we describe the first atomic structure of a natural cognate TCR in complex with this gp100 epitope and highlight the relatively high affinity of the interaction. Alanine scan mutagenesis performed across the gp100(280-288) peptide showed that Glu(3) was critically important for TCR binding. Unexpectedly, structural analysis demonstrated that the Glu(3) â Ala substitution resulted in a molecular switch that was transmitted to adjacent residues, abrogating TCR binding and T-cell recognition. These findings help to clarify the mechanism of T-cell recognition of gp100 during melanoma responses and could direct the development of altered peptides for vaccination.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Melanoma/imunologia , Receptores de Antígenos de Linfócitos T/química , Receptores de Antígenos de Linfócitos T/imunologia , Antígeno gp100 de Melanoma/química , Antígeno gp100 de Melanoma/imunologia , Linfócitos T CD8-Positivos/patologia , Humanos , Melanoma/genética , Melanoma/patologia , Estrutura Quaternária de Proteína , Receptores de Antígenos de Linfócitos T/genética , Antígeno gp100 de Melanoma/genéticaRESUMO
Pmel17 is a multidomain protein involved in biosynthesis of melanin. This process is facilitated by the formation of Pmel17 amyloid fibrils that serve as a scaffold, important for pigment deposition in melanosomes. A specific luminal domain of human Pmel17, containing 10 tandem imperfect repeats, designated as repeat domain (RPT), forms amyloid fibrils in a pH-controlled mechanism in vitro and has been proposed to be essential for the formation of the fibrillar matrix. Currently, no three-dimensional structure has been resolved for the RPT domain of Pmel17. Here, we examine the structure of the RPT domain by performing sequence threading. The resulting model was subjected to energy minimization and validated through extensive molecular dynamics simulations. Structural analysis indicated that the RPT model exhibits several distinct properties of ß-solenoid structures, which have been proposed to be polymerizing components of amyloid fibrils. The derived model is stabilized by an extensive network of hydrogen bonds generated by stacking of highly conserved polar residues of the RPT domain. Furthermore, the key role of invariant glutamate residues is proposed, supporting a pH-dependent mechanism for RPT domain assembly. Conclusively, our work attempts to provide structural insights into the RPT domain structure and to elucidate its contribution to Pmel17 amyloid fibril formation.
Assuntos
Amiloide/química , Melanossomas/química , Sequências Repetitivas de Aminoácidos/genética , Antígeno gp100 de Melanoma/química , Humanos , Melanossomas/genética , Conformação Proteica , Domínios Proteicos , Estrutura Terciária de Proteína , Antígeno gp100 de Melanoma/genéticaRESUMO
Pmel17 is the major component of functional amyloid fibrils that have an important role during pigment deposition. Pmel17 polymerization is promoted within the mildly acidic conditions of melanosomes, organelles located in pigment-specific cells. A repeat domain (RPT domain) of Pmel17, rich in glutamic acid residues has been extensively associated with the formation of the fibrous matrix. Here, we examine the RPT domain of human Pmel17 in order to provide information on this mechanism. Specifically, we have identified an aggregation-prone peptide segment ((405) VSIVVLSGT(413) ), close to the C-terminal part of the RPT domain. Experimental results utilizing electron microscopy, X-ray fiber diffraction, Congo red staining and ATR FT-IR spectroscopy indicate that this peptide segment self-assembles forming fibrils with evident amyloidogenic properties. Conclusively, our results demonstrate that the (405) VSIVVLSGT(413) peptide segment possibly has an essential role in RPT domain fibrillogenesis.