RESUMEN
Many neurotransmitter receptors activate G proteins through exchange of GDP for GTP. The intermediate nucleotide-free state has eluded characterization, due largely to its inherent instability. Here we characterize a G protein variant associated with a rare neurological disorder in humans. GαoK46E has a charge reversal that clashes with the phosphate groups of GDP and GTP. As anticipated, the purified protein binds poorly to guanine nucleotides yet retains wild-type affinity for G protein ßγ subunits. In cells with physiological concentrations of nucleotide, GαoK46E forms a stable complex with receptors and Gßγ, impeding effector activation. Further, we demonstrate that the mutant can be easily purified in complex with dopamine-bound D2 receptors, and use cryo-electron microscopy to determine the structure, including both domains of Gαo, without nucleotide or stabilizing nanobodies. These findings reveal the molecular basis for the first committed step of G protein activation, establish a mechanistic basis for a neurological disorder, provide a simplified strategy to determine receptor-G protein structures, and a method to detect high affinity agonist binding in cells.
Asunto(s)
Microscopía por Crioelectrón , Guanosina Difosfato , Guanosina Trifosfato , Mutación , Humanos , Células HEK293 , Guanosina Difosfato/metabolismo , Guanosina Trifosfato/metabolismo , Trastornos del Neurodesarrollo/genética , Trastornos del Neurodesarrollo/metabolismo , Receptores de Dopamina D2/metabolismo , Receptores de Dopamina D2/genética , Subunidades alfa de la Proteína de Unión al GTP Gi-Go/metabolismo , Subunidades alfa de la Proteína de Unión al GTP Gi-Go/genética , Subunidades alfa de la Proteína de Unión al GTP Gi-Go/química , Unión Proteica , Proteínas de Unión al GTP/metabolismo , Proteínas de Unión al GTP/genética , Subunidades gamma de la Proteína de Unión al GTP/metabolismo , Subunidades gamma de la Proteína de Unión al GTP/genéticaRESUMEN
Allosteric regulation of inosine 5'-monophosphate dehydrogenase (IMPDH), an essential enzyme of purine metabolism, contributes to the homeostasis of adenine and guanine nucleotides. However, the precise molecular mechanism of IMPDH regulation in bacteria remains unclear. Using biochemical and cryo-EM approaches, we reveal the intricate molecular mechanism of the IMPDH allosteric regulation in mycobacteria. The enzyme is inhibited by both GTP and (p)ppGpp, which bind to the regulatory CBS domains and, via interactions with basic residues in hinge regions, lock the catalytic core domains in a compressed conformation. This results in occlusion of inosine monophosphate (IMP) substrate binding to the active site and, ultimately, inhibition of the enzyme. The GTP and (p)ppGpp allosteric effectors bind to their dedicated sites but stabilize the compressed octamer by a common mechanism. Inhibition is relieved by the competitive displacement of GTP or (p)ppGpp by ATP allowing IMP-induced enzyme expansion. The structural knowledge and mechanistic understanding presented here open up new possibilities for the development of allosteric inhibitors with antibacterial potential.
Asunto(s)
Guanosina Trifosfato , IMP Deshidrogenasa , IMP Deshidrogenasa/metabolismo , IMP Deshidrogenasa/química , IMP Deshidrogenasa/antagonistas & inhibidores , Regulación Alostérica , Guanosina Trifosfato/metabolismo , Microscopía por Crioelectrón , Dominio Catalítico , Modelos Moleculares , Proteínas Bacterianas/metabolismo , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Guanosina Pentafosfato/metabolismo , Inosina Monofosfato/metabolismo , Inosina Monofosfato/química , Unión Proteica , Adenosina Trifosfato/metabolismo , Mycobacterium smegmatis/enzimología , Mycobacterium smegmatis/metabolismoRESUMEN
RAS GTPases associate with the biological membrane where they function as molecular switches to regulate cell growth. Recent studies indicate that RAS proteins oligomerize on membranes, and disrupting these assemblies represents an alternative therapeutic strategy. However, conflicting reports on RAS assemblies, ranging in size from dimers to nanoclusters, have brought to the fore key questions regarding the stoichiometry and parameters that influence oligomerization. Here, we probe three isoforms of RAS [Kirsten Rat Sarcoma viral oncogene (KRAS), Harvey Rat Sarcoma viral oncogene (HRAS), and Neuroblastoma oncogene (NRAS)] directly from membranes using mass spectrometry. We show that KRAS on membranes in the inactive state (GDP-bound) is monomeric but forms dimers in the active state (GTP-bound). We demonstrate that the small molecule BI2852 can induce dimerization of KRAS, whereas the binding of effector proteins disrupts dimerization. We also show that RAS dimerization is dependent on lipid composition and reveal that oligomerization of NRAS is regulated by palmitoylation. By monitoring the intrinsic GTPase activity of RAS, we capture the emergence of a dimer containing either mixed nucleotides or GDP on membranes. We find that the interaction of RAS with the catalytic domain of Son of Sevenless (SOScat) is influenced by membrane composition. We also capture the activation and monomer to dimer conversion of KRAS by SOScat. These results not only reveal the stoichiometry of RAS assemblies on membranes but also uncover the impact of critical factors on oligomerization, encompassing regulation by nucleotides, lipids, and palmitoylation.
Asunto(s)
Membrana Celular , Multimerización de Proteína , Proteínas Proto-Oncogénicas p21(ras) , Proteínas Proto-Oncogénicas p21(ras)/metabolismo , Proteínas Proto-Oncogénicas p21(ras)/genética , Proteínas Proto-Oncogénicas p21(ras)/química , Humanos , Membrana Celular/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/química , Proteínas de la Membrana/genética , GTP Fosfohidrolasas/metabolismo , GTP Fosfohidrolasas/química , GTP Fosfohidrolasas/genética , Lipoilación , Proteínas ras/metabolismo , Proteínas ras/química , Guanosina Trifosfato/metabolismo , Guanosina Difosfato/metabolismoRESUMEN
FtsZ is highly conserved among bacteria and plays an essential role in bacterial cell division. The tense conformation of FtsZ bound to GTP assembles into a straight filament via head-to-tail associations, and then the upper subunit of FtsZ hydrolyzes GTP bound to the lower FtsZ subunit. The subunit with GDP bound disassembles accompanied by a conformational change in the subunit from the tense to relaxed conformation. Although crystal structures of FtsZ derived from several bacterial species have been determined, the conformational change from the relaxed to tense conformation has only been observed in Staphylococcus aureus FtsZ (SaFtsZ). Recent cryo-electron microscopy analyses revealed the three-dimensional reconstruction of the protofilament, in which tense molecules assemble via head-to-tail associations. However, the lower resolution of the protofilament suggested that the flexibility of the FtsZ protomers between the relaxed and tense conformations caused them to form in less-strict alignments. Furthermore, this flexibility may also prevent FtsZs other than SaFtsZ from crystalizing in the tense conformation, suggesting that the flexibility of bacterial FtsZs differs. In this study, molecular dynamics simulations were performed using SaFtsZ and Bacillus subtilis FtsZ in several situations, which suggested that different features of the FtsZs affect their conformational stability.
Asunto(s)
Bacillus subtilis , Proteínas Bacterianas , Proteínas del Citoesqueleto , Simulación de Dinámica Molecular , Conformación Proteica , Staphylococcus aureus , Proteínas del Citoesqueleto/metabolismo , Proteínas del Citoesqueleto/química , Bacillus subtilis/metabolismo , Bacillus subtilis/química , Proteínas Bacterianas/química , Proteínas Bacterianas/metabolismo , Staphylococcus aureus/metabolismo , Staphylococcus aureus/química , Estabilidad Proteica , Guanosina Trifosfato/metabolismo , Guanosina Trifosfato/químicaRESUMEN
A host of metabolic enzymes reversibly self-assemble to form membrane-less, intracellular filaments under normal physiological conditions and in response to stress. Often, these enzymes reside at metabolic control points, suggesting that filament formation affords an additional regulatory mechanism. Examples include cytidine-5'-triphosphate (CTP) synthase (CTPS), which catalyzes the rate-limiting step for the de novo biosynthesis of CTP; inosine-5'-monophosphate dehydrogenase (IMPDH), which controls biosynthetic access to guanosine-5'-triphosphate (GTP); and ∆1-pyrroline-5-carboxylate (P5C) synthase (P5CS) that catalyzes the formation of P5C, which links the Krebs cycle, urea cycle, and proline metabolism. Intriguingly, CTPS can exist in co-assemblies with IMPDH or P5CS. Since GTP is an allosteric activator of CTPS, the association of CTPS and IMPDH filaments accords with the need to coordinate pyrimidine and purine biosynthesis. Herein, a hypothesis is presented furnishing a biochemical connection underlying co-assembly of CTPS and P5CS filaments - potent inhibition of CTPS by glutamate γ-semialdehyde, the open-chain form of P5C.
Asunto(s)
Ligasas de Carbono-Nitrógeno , IMP Deshidrogenasa , Animales , Humanos , Ligasas de Carbono-Nitrógeno/metabolismo , Ligasas de Carbono-Nitrógeno/genética , Citidina Trifosfato/metabolismo , Guanosina Trifosfato/metabolismo , IMP Deshidrogenasa/metabolismoRESUMEN
Mitofusins (Mfn1 and Mfn2) are the mitochondrial outer-membrane fusion proteins in mammals and belong to the dynamin superfamily of multidomain GTPases. Recent structural studies of truncated variants lacking alpha helical transmembrane domains suggested that Mfns dimerize to promote the approximation and the fusion of the mitochondrial outer membranes upon the hydrolysis of guanine 5'-triphosphate disodium salt (GTP). However, next to the presence of GTP, the fusion activity seems to require multiple regulatory factors that control the dynamics and kinetics of mitochondrial fusion through the formation of Mfn1-Mfn2 heterodimers. Here, we purified and reconstituted the full-length murine Mfn2 protein into giant unilamellar vesicles (GUVs) with different lipid compositions. The incubation with GTP resulted in the fusion of Mfn2-GUVs. High-speed video-microscopy showed that the Mfn2-dependent membrane fusion pathway progressed through a zipper mechanism where the formation and growth of an adhesion patch eventually led to the formation of a membrane opening at the rim of the septum. The presence of physiological concentration (up to 30 mol%) of dioleoyl-phosphatidylethanolamine (DOPE) was shown to be a requisite to observe GTP-induced Mfn2-dependent fusion. Our observations show that Mfn2 alone can promote the fusion of micron-sized DOPE-enriched vesicles without the requirement of regulatory cofactors, such as membrane curvature, or the assistance of other proteins.
Asunto(s)
GTP Fosfohidrolasas , Fusión de Membrana , Animales , GTP Fosfohidrolasas/metabolismo , GTP Fosfohidrolasas/genética , Ratones , Fusión de Membrana/fisiología , Liposomas Unilamelares/metabolismo , Liposomas Unilamelares/química , Guanosina Trifosfato/metabolismo , Fosfatidiletanolaminas/metabolismo , Membranas Mitocondriales/metabolismo , Proteínas Mitocondriales/metabolismo , Proteínas Mitocondriales/genética , Mitocondrias/metabolismoRESUMEN
RAS proteins are conserved guanosine triphosphate (GTP) hydrolases (GTPases) that act as molecular binary switches and play vital roles in numerous cellular processes. Upon GTP binding, RAS GTPases adopt an active conformation and interact with specific proteins termed RAS effectors that contain a conserved ubiquitin-like domain, thereby facilitating downstream signaling. Over 50 effector proteins have been identified in the human proteome, and many have been studied as potential mediators of RAS-dependent signaling pathways. Biochemical and structural analyses have provided mechanistic insights into these effectors, and studies using model organisms have complemented our understanding of their role in physiology and disease. Yet, many critical aspects regarding the dynamics and biological function of RAS-effector complexes remain to be elucidated. In this review, we discuss the mechanisms and functions of known RAS effector proteins, provide structural perspectives on RAS-effector interactions, evaluate their significance in RAS-mediated signaling, and explore their potential as therapeutic targets.
Asunto(s)
Transducción de Señal , Proteínas ras , Humanos , Proteínas ras/metabolismo , Proteínas ras/química , Animales , Unión Proteica , Modelos Moleculares , Relación Estructura-Actividad , Conformación Proteica , Guanosina Trifosfato/metabolismoRESUMEN
The wildtype H-Ras protein functions as a molecular switch in a variety of cell signaling pathways, and mutations to key residues result in a constitutively active oncoprotein. However, there is some debate regarding the mechanism of the intrinsic GTPase activity of H-Ras. It has been hypothesized that ordered water molecules are coordinated at the active site by Q61, a highly transforming amino acid site, and Y32, a position that has not previously been investigated. Here, we examine the electrostatic contribution of the Y32 position to GTP hydrolysis by comparing the rate of GTP hydrolysis of Y32X mutants to the vibrational energy shift of each mutation measured by a nearby thiocyanate vibrational probe to estimate changes in the electrostatic environment caused by changes at the Y32 position. We further compared vibrational energy shifts for each mutation to the hydration potential of the respective side chain and demonstrated that Y32 is less critical for recruiting water molecules into the active site to promote hydrolysis than Q61. Our results show a clear interplay between a steric contribution from Y32 and an electrostatic contribution from Q61 that are both critical for intrinsic GTP hydrolysis.
Asunto(s)
Guanosina Trifosfato , Electricidad Estática , Tiocianatos , Hidrólisis , Tiocianatos/química , Tiocianatos/metabolismo , Guanosina Trifosfato/metabolismo , Guanosina Trifosfato/química , Humanos , Proteínas Proto-Oncogénicas p21(ras)/genética , Proteínas Proto-Oncogénicas p21(ras)/química , Proteínas Proto-Oncogénicas p21(ras)/metabolismo , Tirosina/química , Tirosina/metabolismo , Tirosina/genética , Mutación , Dominio Catalítico , Agua/química , Agua/metabolismo , Modelos MolecularesRESUMEN
In many animal species, the oocyte meiotic spindle, which is required for chromosome segregation, forms without centrosomes. In some systems, Ran-GEF on chromatin initiates spindle assembly. We found that in Caenorhabditis elegans oocytes, endogenously-tagged Ran-GEF dissociates from chromatin during spindle assembly but re-associates during meiotic anaphase. Meiotic spindle assembly occurred after auxin-induced degradation of Ran-GEF, but anaphase I was faster than controls and extrusion of the first polar body frequently failed. In search of a possible alternative pathway for spindle assembly, we found that soluble tubulin concentrates in the nuclear volume during germinal vesicle breakdown. We found that the concentration of soluble tubulin in the metaphase spindle region is enclosed by ER sheets which exclude cytoplasmic organelles including mitochondria and yolk granules. Measurement of the volume occupied by yolk granules and mitochondria indicated that volume exclusion would be sufficient to explain the concentration of tubulin in the spindle volume. We suggest that this concentration of soluble tubulin may be a redundant mechanism promoting spindle assembly near chromosomes.
Asunto(s)
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans , Meiosis , Oocitos , Tubulina (Proteína) , Proteína de Unión al GTP ran , Animales , Anafase , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Cromatina/metabolismo , Segregación Cromosómica , Guanosina Trifosfato/metabolismo , Meiosis/fisiología , Oocitos/metabolismo , Prometafase , Proteína de Unión al GTP ran/metabolismo , Huso Acromático/metabolismo , Tubulina (Proteína)/metabolismoRESUMEN
Small GTPases switch between GDP- and GTP-bound states during cell signaling. The ADP-ribosylation factor (ARF) family of small GTPases is involved in vesicle trafficking. Although evolutionarily well conserved, little is known about ARF and ARF-like GTPases in plants. We characterized biochemical properties and cellular localization of the essential small ARF-like GTPase TITAN 5 (TTN5; also known as HALLIMASCH, ARL2 and ARLC1) from Arabidopsis thaliana, and two TTN5 proteins with point mutants in conserved residues, TTN5T30N and TTN5Q70L, that were expected to be unable to perform nucleotide exchange and GTP hydrolysis, respectively. TTN5 exhibited very rapid intrinsic nucleotide exchange and remarkably low GTP hydrolysis activity, functioning as a non-classical small GTPase being likely present in a GTP-loaded active form. We analyzed signals from YFP-TTN5 and HA3-TTN5 by in situ immunolocalization in Arabidopsis seedlings and through use of a transient expression system. Colocalization with endomembrane markers and pharmacological treatments suggests that TTN5 can be present at the plasma membrane and that it dynamically associates with membranes of vesicles, Golgi stacks and multivesicular bodies. Although TTN5Q70L mirrored wild-type TTN5 behavior, the TTN5T30N mutant differed in some aspects. Hence, the unusual rapid nucleotide exchange activity of TTN5 is linked with its membrane dynamics, and TTN5 likely has a role in vesicle transport within the endomembrane system.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Guanosina Trifosfato/metabolismo , Membrana Celular/metabolismo , Factores de Ribosilacion-ADP/metabolismo , Factores de Ribosilacion-ADP/genética , Hidrólisis , Aparato de Golgi/metabolismoRESUMEN
How nucleocytoplasmic transport (NCT) rates change due to cellular physiology-mediated fluctuations in GTP availability remains unclear. In this issue, Scott et al. (https://doi.org/10.1083/jcb.202308152) demonstrate that cell migration, spreading, and nucleocytoskeletal coupling impact GTP levels, thereby regulating NCT, RNA export, and protein synthesis.
Asunto(s)
Transporte Activo de Núcleo Celular , Metabolismo Energético , Humanos , Movimiento Celular , Núcleo Celular/metabolismo , Guanosina Trifosfato/metabolismo , Biosíntesis de ProteínasRESUMEN
The purine nucleotides ATP and GTP are made from the common precursor inosine monophosphate (IMP). Maintaining the correct balance of these nucleotides for optimal cell growth is controlled in part by the enzyme IMP dehydrogenase (IMPDH), which catalyzes the first dedicated step of GTP biosynthesis. The regulation of IMPDH mRNA and protein levels in the yeast S. cerevisiae grown in liquid culture has been studied in some detail, but regulation of IMPDH protein under conditions of cellular crowding on a solid substrate has not been examined. Here, we report real-time, live-cell analysis of the accumulation of the Imd2 isoform of IMPDH in yeast cells forming a monolayer colony in a microfluidic device over a 50-hour time course. We observe two distinct phases of increased Imd2 accumulation: a guanine-insensitive phase early in outgrowth and a guanine-sensitive phase later, when cells become crowded. We show that the IMPDH inhibitor mycophenolic acid enhances both phases of increase. Deletion of a transcription attenuator upstream of the mRNA start site that decreases Imd2 mRNA synthesis in the presence of high GTP increases the baseline level of Imd2 protein 10-fold and abolishes guanine-sensitive but not guanine-insensitive induction. Our results suggest that at least two mechanisms of yeast Imd2 regulation exist, the known GTP-dependent attenuation of RNA polymerase II elongation and a GTP concentration-independent pathway that may be controlled by cell growth state. Live-cell analysis of IMPDH protein levels in a growing yeast colony confirms a known mechanism of regulation and provides evidence for an additional mode of regulation. IMPORTANCE: This study used live-cell microscopy to track changes in the level of a key enzyme in GTP nucleotide biosynthesis, inosine monophosphate dehydrogenase (IMPDH), during growth of a brewers yeast colony over 2 days in a microfluidic device. The results show that feedback regulation via transcription attenuation allows cells to adapt to nutrient limitation in the crowded environs of a yeast colony. They also identify a novel mode of regulation of IMPDH level that is not driven by guanine nucleotide availability.
Asunto(s)
Regulación Fúngica de la Expresión Génica , Guanosina Trifosfato , IMP Deshidrogenasa , Saccharomyces cerevisiae , IMP Deshidrogenasa/metabolismo , IMP Deshidrogenasa/genética , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/crecimiento & desarrollo , Guanosina Trifosfato/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Ácido Micofenólico/farmacologíaRESUMEN
Gliomas are the most common primary tumors of the central nervous system, with approximately half of patients presenting with the most aggressive form of glioblastoma. Although several molecular markers for glioma have been identified, they are not sufficient to predict the prognosis due to the extensive genetic heterogeneity within glioma. Our study reveals that the ratio of IMPDH1 to IMPDH2 expression levels serves as a molecular indicator for glioma treatment prognosis. Patients with a higher IMPDH1/IMPDH2 ratio exhibit a worse prognosis, while those with a lower ratio display a more favorable prognosis. We further demonstrate that IMPDH1 plays a crucial role in maintaining cellular GTP/GDP levels following DNA damage compared to IMPDH2. In the absence of IMPDH1, cells experience an imbalance in the GTP/GDP ratio, impairing DNA damage repair capabilities and rendering them more sensitive to TMZ. This study not only introduces a novel prognostic indicator for glioma clinical diagnosis but also offers innovative insights for precise and stratified glioma treatment.
Asunto(s)
Glioma , IMP Deshidrogenasa , Temozolomida , Humanos , Glioma/tratamiento farmacológico , Glioma/genética , Glioma/patología , Glioma/mortalidad , IMP Deshidrogenasa/genética , IMP Deshidrogenasa/metabolismo , Temozolomida/uso terapéutico , Temozolomida/farmacología , Pronóstico , Neoplasias Encefálicas/tratamiento farmacológico , Neoplasias Encefálicas/genética , Neoplasias Encefálicas/patología , Línea Celular Tumoral , Daño del ADN/efectos de los fármacos , Femenino , Masculino , Guanosina Trifosfato/metabolismoRESUMEN
Rab3A is a member of the Rab GTPase family involved in synaptic vesicle trafficking. Recent evidence has demonstrated that Rab3A is phosphorylated by leucine-rich repeat kinase 2 (LRRK2) that is implicated in both familial and sporadic forms of Parkinson's disease (PD), and an abnormal increase in Rab3A phosphorylation has been proposed as a cause of PD. Despite the potential importance of Rab3A in PD pathogenesis, its structural information is limited and the effects of bound nucleotides on its biophysical and biochemical properties remain unclear. Here, we show that GDP-bound Rab3A is preferentially phosphorylated by LRRK2 compared with GTP-bound Rab3A. The secondary structure of Rab3A, measured by circular dichroism (CD) spectroscopy, revealed that Rab3A is resistant to heat-induced denaturation at pH 7.4 or 9.0 regardless of the nucleotides bound. In contrast, Rab3A underwent heat-induced denaturation at pH 5.0 at a lower temperature in its GDP-bound form than in its GTP-bound form. The unfolding temperature of Rab3A was studied by differential scanning fluorimetry, which showed a significantly higher unfolding temperature in GTP-bound Rab3A than in GDP-bound Rab3A, with the highest at pH 7.4. These results suggest that Rab3A has unusual thermal stability under physiologically relevant conditions and that bound nucleotides influence both thermal stability and phosphorylation by LRRK2.
Asunto(s)
Guanosina Difosfato , Guanosina Trifosfato , Proteína 2 Quinasa Serina-Treonina Rica en Repeticiones de Leucina , Estructura Secundaria de Proteína , Proteína de Unión al GTP rab3A , Fosforilación , Guanosina Trifosfato/metabolismo , Guanosina Trifosfato/química , Humanos , Proteína 2 Quinasa Serina-Treonina Rica en Repeticiones de Leucina/metabolismo , Proteína 2 Quinasa Serina-Treonina Rica en Repeticiones de Leucina/química , Proteína 2 Quinasa Serina-Treonina Rica en Repeticiones de Leucina/genética , Proteína de Unión al GTP rab3A/metabolismo , Proteína de Unión al GTP rab3A/química , Guanosina Difosfato/metabolismo , Guanosina Difosfato/química , Estabilidad ProteicaRESUMEN
Membrane protrusions are fundamental to cellular functions like migration, adhesion, and communication and depend upon dynamic reorganization of the cytoskeleton. GAP-dependent GTP hydrolysis of Arf proteins regulates actin-dependent membrane remodeling. Here, we show that dAsap regulates membrane protrusions in S2R+ cells by a mechanism that critically relies on its ArfGAP domain and relocalization of actin regulators, SCAR, and Ena. While our data reinforce the preference of dAsap for Arf1 GTP hydrolysis in vitro, we demonstrate that induction of membrane protrusions in S2R+ cells depends on Arf6 inactivation. This study furthers our understanding of how dAsap-dependent GTP hydrolysis maintains a balance between active and inactive states of Arf6 to regulate cell shape.
Asunto(s)
Factor 6 de Ribosilación del ADP , Factores de Ribosilacion-ADP , Actinas , Proteínas Activadoras de GTPasa , Animales , Factores de Ribosilacion-ADP/metabolismo , Factores de Ribosilacion-ADP/genética , Proteínas Activadoras de GTPasa/metabolismo , Proteínas Activadoras de GTPasa/genética , Actinas/metabolismo , Ratones , Extensiones de la Superficie Celular/metabolismo , Humanos , Línea Celular , Guanosina Trifosfato/metabolismo , HidrólisisRESUMEN
Eukaryotic and archaeal translation initiation factor 2 in complex with GTP delivers the initiator methionyl-tRNA to the small ribosomal subunit. Over the past 20 years, thanks to the efforts of various research groups, including ours, this factor from the archaeon Sulfolobus solfataricus and its individual subunits have been crystallized in ten different space groups. Analysis of the molecular packing in these crystals makes it possible to better understand the roles of functionally significant switches and other elements of the nucleotide-binding pocket during the function of the factor as well as the influence of external effects on its transition between active and inactive states.
Asunto(s)
Proteínas Arqueales , Sulfolobus solfataricus , Sulfolobus solfataricus/química , Sulfolobus solfataricus/metabolismo , Proteínas Arqueales/química , Proteínas Arqueales/metabolismo , Cristalografía por Rayos X , Modelos Moleculares , Guanosina Trifosfato/metabolismo , Guanosina Trifosfato/química , Factores de Iniciación de Péptidos/química , Factores de Iniciación de Péptidos/metabolismo , Conformación Proteica , Sitios de Unión , ARN de Transferencia de Metionina/química , ARN de Transferencia de Metionina/metabolismoRESUMEN
Bacterial cell division is crucial for replication and requires careful coordination via proteins collectively called the divisome. The tubulin-like GTPase FtsZ is the master regulator of this process and serves to recruit downstream divisome proteins and regulate their activities. Upon assembling at mid-cell, FtsZ exhibits treadmilling motion driven by GTP binding and hydrolysis. Treadmilling is proposed to play roles in Z-ring condensation and in distribution and regulation of peptidoglycan (PG) cell wall enzymes. FtsZ polymer superstructure and dynamics are central to its function, yet their regulation is incompletely understood. We addressed these gaps in knowledge by evaluating the contribution of GTPase activity to FtsZ's function in vitro and in Caulobacter crescentus cells. We observed that a lethal mutation that abrogates FtsZ GTP hydrolysis impacts FtsZ dynamics and Z-ring positioning, but not constriction. Aberrant Z-ring positioning was due to insensitivity to the FtsZ regulator MipZ when GTPase activity is reduced. Z-ring mislocalization resulted in DNA damage, likely due to constriction over the nucleoid. Collectively, our results indicate that GTP hydrolysis serves primarily to position the Z-ring at mid-cell in Caulobacter. Proper Z-ring localization is required for effective coordination with chromosome segregation to prevent DNA damage and ensure successful cell division.
Asunto(s)
Proteínas Bacterianas , Caulobacter crescentus , División Celular , Proteínas del Citoesqueleto , GTP Fosfohidrolasas , Guanosina Trifosfato , Caulobacter crescentus/metabolismo , Caulobacter crescentus/genética , Proteínas Bacterianas/metabolismo , Proteínas del Citoesqueleto/metabolismo , Guanosina Trifosfato/metabolismo , GTP Fosfohidrolasas/metabolismo , División Celular/fisiología , Hidrólisis , MutaciónRESUMEN
Continuous fusion and fission are critical for mitochondrial health. In this study, we further characterize the role played by dynamin-related protein 1 (Drp1) in mitochondrial fission. We show that a single amino acid change in Drp1 at position 39 from serine to alanine (S39A) within the GTP-binding (GTPase) domain results in a fused mitochondrial network in human SH-SY5Y neuroblastoma cells. Interestingly, the phosphorylation of Ser-616 and Ser-637 of Drp1 remains unaffected by the S39A mutation, and mitochondrial bioenergetic profile and cell viability in the S39A mutant were comparable to those observed in the control. This leads us to propose that the serine 39 residue of Drp1 plays a crucial role in mitochondrial distribution through its involvement in the GTPase activity. Furthermore, this amino acid mutation leads to structural anomalies in the mitochondrial network. Taken together, our results contribute to a better understanding of the function of the Drp1 protein.
Asunto(s)
Dinaminas , Mitocondrias , Dinámicas Mitocondriales , Serina , Humanos , Dinaminas/metabolismo , Dinaminas/genética , Mitocondrias/metabolismo , Serina/metabolismo , Serina/genética , Dinámicas Mitocondriales/genética , Guanosina Trifosfato/metabolismo , Línea Celular Tumoral , Fosforilación , Mutación , GTP Fosfohidrolasas/metabolismo , GTP Fosfohidrolasas/genéticaRESUMEN
Rab6 is a key modulator of protein secretion. The dynein adapter Bicaudal D2 (BicD2) recruits the motors cytoplasmic dynein and kinesin-1 to Rab6GTP-positive vesicles for transport; however, it is unknown how BicD2 recognizes Rab6. Here, we establish a structural model for recognition of Rab6GTP by BicD2, using structure prediction and mutagenesis. The binding site of BicD2 spans two regions of Rab6 that undergo structural changes upon the transition from the GDP- to GTP-bound state, and several hydrophobic interface residues are rearranged, explaining the increased affinity of the active GTP-bound state. Mutations of Rab6GTP that abolish binding to BicD2 also result in reduced co-migration of Rab6GTP/BicD2 in cells, validating our model. These mutations also severely diminished the motility of Rab6-positive vesicles in cells, highlighting the importance of the Rab6GTP/BicD2 interaction for overall motility of the multi-motor complex that contains both kinesin-1 and dynein. Our results provide insights into trafficking of secretory and Golgi-derived vesicles and will help devise therapies for diseases caused by BicD2 mutations, which selectively affect the affinity to Rab6 and other cargoes.