A Molecular Analysis of the Aminopeptidase P-Related Domain of PID-5 from Caenorhabditis elegans.

A novel protein, PID-5, has been shown to be a requirement for germline immortality and has recently been implicated in RNA-induced epigenetic silencing in the Caenorhabditis elegans embryo. Importantly, it has been shown to contain both an eTudor and aminopeptidase P-related domain. However, the silencing mechanism has not yet been fully characterised. In this study, bioinformatic tools were used to compare pre-existing aminopeptidase P molecular structures to the AlphaFold2-predicted aminopeptidase P-related domain of PID-5 (PID-5 APP-RD). Structural homology, metal composition, inhibitor-bonding interactions, and the potential for dimerisation were critically assessed through computational techniques, including structural superimposition and protein-ligand docking. Results from this research suggest that the metallopeptidase-like domain shares high structural homology with known aminopeptidase P enzymes and possesses the canonical 'pita-bread fold'. However, the absence of conserved metal-coordinating residues indicates that only a single Zn2+ may be bound at the active site. The PID-5 APP-RD may form transient interactions with a known aminopeptidase P inhibitor and may therefore recognise substrates in a comparable way to the known structures. However, loss of key catalytic residues suggests the domain will be inactive. Further evidence suggests that heterodimerisation with C. elegans aminopeptidase P is feasible and therefore PID-5 is predicted to regulate proteolytic cleavage in the silencing pathway. PID-5 may interact with PID-2 to bring aminopeptidase P activity to the Z-granule, where it could influence WAGO-4 activity to ensure the balanced production of 22G-RNA signals for transgenerational silencing. Targeted experiments into APPs implicated in malaria and cancer are required in order to build upon the biological and therapeutic significance of this research.

The LL-37 domain: A clue to cathelicidin immunomodulatory response?

Host defense peptides (HDPs) are naturally occurring polypeptide sequences that, in addition to being active against bacteria, fungi, viruses, and other parasites, may stimulate immunomodulatory responses. Cathelicidins, a family of HDPs, are produced by diverse animal species, such as mammals, fish, birds, amphibians, and reptiles, to protect them against pathogen infections. These peptides have variable C-terminal domains responsible for their antimicrobial and immunomodulatory activities and a highly conserved N-terminal pre-pro region homologous to cathelin. Although cathelicidins are the major components of innate immunity, the molecular basis by which they induce an immune response is still unclear. In this review, we will address the role of the LL-37 domain and its SK-24, IV-20, FK-13 and LL-37 fragments in the immunity response. Other cathelicidins also share structural and functional characteristics with the LL-37 domain, suggesting that these fragments may be responsible for interaction between these peptides and receptors in humans. Fragments of the LL-37 domain can give us clues about how homologous cathelicidins, in general, induce an immune response.

Staphylococcal Periscope proteins Aap, SasG, and Pls project noncanonical legume-like lectin adhesin domains from the bacterial surface.

Staphylococcus aureus and Staphylococcus epidermidis are frequently associated with medical device infections that involve establishment of a bacterial biofilm on the device surface. Staphylococcal surface proteins Aap, SasG, and Pls are members of the Periscope Protein class and have been implicated in biofilm formation and host colonization; they comprise a repetitive region ("B region") and an N-terminal host colonization domain within the "A region," predicted to be a lectin domain. Repetitive E-G5 domains (as found in Aap, SasG, and Pls) form elongated "stalks" that would vary in length with repeat number, resulting in projection of the N-terminal A domain variable distances from the bacterial cell surface. Here, we present the structures of the lectin domains within A regions of SasG, Aap, and Pls and a structure of the Aap lectin domain attached to contiguous E-G5 repeats, suggesting the lectin domains will sit at the tip of the variable length rod. We demonstrate that these isolated domains (Aap, SasG) are sufficient to bind to human host desquamated nasal epithelial cells. Previously, proteolytic cleavage or a deletion within the A domain had been reported to induce biofilm formation; the structures suggest a potential link between these observations. Intriguingly, while the Aap, SasG, and Pls lectin domains bind a metal ion, they lack the nonproline cis peptide bond thought to be key for carbohydrate binding by the lectin fold. This suggestion of noncanonical ligand binding should be a key consideration when investigating the host cell interactions of these bacterial surface proteins.

α-synuclein and phosphoinositide-binding proteins: α-synuclein inhibits the association of PX- but not FYVE-containing proteins with vesicles in vivo.

By an unknown mechanism, alpha-synuclein (α-syn) inhibits autophagy in yeast and human cells. Herein, using the yeast Saccharomyces cerevisiae, we tested the hypothesis that α-syn disrupts autophagy by inhibiting the required association of sorting nexin 4 (Snx4) with phagophores. Snx4 contains a phox (PX) homology domain that selectively binds membranes enriched in phosphatidylinositol 3-phosphate (PI3P). Using fluorescence microscopy, we show that upon nitrogen starvation, 70% of the cells exhibited green puncta (phagophores); whereas identically treated cells expressing α-syn exhibited a significantly lower percentage of cells (30%) with such puncta. Our interpretation is that α-syn outcompetes Snx4 for binding to membranes enriched in PI3P, resulting in fewer phagophores and consequently inefficient induction of autophagy. As a control, we tested whether α-syn disrupts the binding of Vps27-GFP to late endosomes/multivesicular bodies (MVBs). Vps27 contains a PI3P-binding domain called FYVE. α-Syn did not disrupt the binding of Vps27-GFP to late endosomes. α-Syn likely inhibits the binding of PX- but not FYVE-containing proteins to PI3P because FYVE domains bind more than two-orders of magnitude tighter than PX domains. We propose that in all cells, whether yeast or human, α-syn has the potential to inhibit protein trafficking pathways that are dependent on PX-domain proteins such as sorting nexins.

Biochemical and Structural Insights into the Winged Helix Domain of P150, the Largest Subunit of the Chromatin Assembly Factor 1.

The Chromatin Assembly Factor 1 is a heterotrimeric complex responsible for the nucleosome assembly during DNA replication and DNA repair. In humans, the largest subunit P150 is the major actor of this process. It has been recently considered as a tumor-associated protein due to its overexpression in many malignancies. Structural and functional studies targeting P150 are still limited and only scarce information about this subunit is currently available. Literature data and bioinformatics analysis assisted the identification of a stable DNA binding domain, encompassing residues from 721 to 860 of P150 within the full-length protein. This domain was recombinantly produced and in vitro investigated. An acidic region modulating its DNA binding ability was also identified and characterized. Results showed similarities and differences between the P150 and its yeast homologue, namely Cac-1, suggesting that, although sharing a common biological function, the two proteins may also possess different features.

A novel effect of PDLIM5 in α7 nicotinic acetylcholine receptor upregulation and surface expression.

Nicotinic acetylcholine receptors (nAChRs) are widespread throughout the central nervous system. Signaling through nAChRs contributes to numerous higher-order functions, including memory and cognition, as well as abnormalities such as nicotine addiction and neurodegenerative disorders. Although recent studies indicate that the PDZ-containing proteins comprising PSD-95 family co-localize with nicotinic acetylcholine receptors and mediate downstream signaling in the neurons, the mechanisms by which α7nAChRs are regulated remain unclear. Here, we show that the PDZ-LIM domain family protein PDLIM5 binds to α7nAChRs and plays a role in nicotine-induced α7nAChRs upregulation and surface expression. We find that chronic exposure to 1 µM nicotine upregulated α7, ß2-contained nAChRs and PDLIM5 in cultured hippocampal neurons, and the upregulation of α7nAChRs and PDLIM5 is increased more on the cell membrane than the cytoplasm. Interestingly, in primary hippocampal neurons, α7nAChRs and ß2nAChRs display distinct patterns of expression, with α7nAChRs colocalized more with PDLIM5. Furthermore, PDLIM5 interacts with α7nAChRs, but not ß2nAChRs in native brain neurons. Knocking down of PDLIM5 in SH-SY5Y abolishes nicotine-induced upregulation of α7nAChRs. In primary hippocampal neurons, using shRNA against PDLIM5 decreased both surface clustering of α7nAChRs and α7nAChRs-mediated currents. Proteomics analysis and isothermal titration calorimetry (ITC) results show that PDLIM5 interacts with α7nAChRs through the PDZ domain, and the interaction between PDLIM5 and α7nAChRs can be promoted by nicotine. Collectively, our data suggest a novel cellular role of PDLIM5 in the regulation of α7nAChRs, which may be relevant to plastic changes in the nervous system.

Is amyloid fibrillation related to 3D domain swapping for the C-terminal domain of SARS-CoV main protease?

The C-terminal domain of SARS-CoV main protease (Mpro-C) can form 3D domain-swapped dimer by exchanging the α1-helices fully buried inside the protein hydrophobic core, under non-denaturing conditions. Here, we report that Mpro-C can also form amyloid fibrils under the 3D domain-swappable conditions in vitro, and the fibrils are not formed through runaway/propagated domain swapping. It is found that there are positive correlations between the rates of domain swapping dimerization and amyloid fibrillation at different temperatures, and for different mutants. However, some Mpro-C mutants incapable of 3D domain swapping can still form amyloid fibrils, indicating that 3D domain swapping is not essential for amyloid fibrillation. Furthermore, NMR H/D exchange data and molecular dynamics simulation results suggest that the protofibril core region tends to unpack at the early stage of 3D domain swapping, so that the amyloid fibrillation can proceed during the 3D domain swapping process. We propose that 3D domain swapping makes it possible for the unpacking of the amyloidogenic fragment of the protein and thus accelerates the amyloid fibrillation process kinetically, which explains the well-documented correlations between amyloid fibrillation and 3D domain swapping observed in many proteins.

Class-specific interactions between Sis1 J-domain protein and Hsp70 chaperone potentiate disaggregation of misfolded proteins.

Protein homeostasis is constantly being challenged with protein misfolding that leads to aggregation. Hsp70 is one of the versatile chaperones that interact with misfolded proteins and actively support their folding. Multifunctional Hsp70s are harnessed to specific roles by J-domain proteins (JDPs, also known as Hsp40s). Interaction with the J-domain of these cochaperones stimulates ATP hydrolysis in Hsp70, which stabilizes substrate binding. In eukaryotes, two classes of JDPs, Class A and Class B, engage Hsp70 in the reactivation of aggregated proteins. In most species, excluding metazoans, protein recovery also relies on an Hsp100 disaggregase. Although intensely studied, many mechanistic details of how the two JDP classes regulate protein disaggregation are still unknown. Here, we explore functional differences between the yeast Class A (Ydj1) and Class B (Sis1) JDPs at the individual stages of protein disaggregation. With real-time biochemical tools, we show that Ydj1 alone is superior to Sis1 in aggregate binding, yet it is Sis1 that recruits more Ssa1 molecules to the substrate. This advantage of Sis1 depends on its ability to bind to the EEVD motif of Hsp70, a quality specific to most of Class B JDPs. This second interaction also conditions the Hsp70-induced aggregate modification that boosts its subsequent dissolution by the Hsp104 disaggregase. Our results suggest that the Sis1-mediated chaperone assembly at the aggregate surface potentiates the entropic pulling, driven polypeptide disentanglement, while Ydj1 binding favors the refolding of the solubilized proteins. Such subspecialization of the JDPs across protein reactivation improves the robustness and efficiency of the disaggregation machinery.

Molecular interactions contributing to FUS SYGQ LC-RGG phase separation and co-partitioning with RNA polymerase II heptads.

The RNA-binding protein FUS (Fused in Sarcoma) mediates phase separation in biomolecular condensates and functions in transcription by clustering with RNA polymerase II. Specific contact residues and interaction modes formed by FUS and the C-terminal heptad repeats of RNA polymerase II (CTD) have been suggested but not probed directly. Here we show how RGG domains contribute to phase separation with the FUS N-terminal low-complexity domain (SYGQ LC) and RNA polymerase II CTD. Using NMR spectroscopy and molecular simulations, we demonstrate that many residue types, not solely arginine-tyrosine pairs, form condensed-phase contacts via several interaction modes including, but not only sp2-π and cation-π interactions. In phases also containing RNA polymerase II CTD, many residue types form contacts, including both cation-π and hydrogen-bonding interactions formed by the conserved human CTD lysines. Hence, our data suggest a surprisingly broad array of residue types and modes explain co-phase separation of FUS and RNA polymerase II.

Ycs4 Subunit of Saccharomyces cerevisiae Condensin Binds DNA and Modulates the Enzyme Turnover.

Condensins play a key role in higher order chromosome organization. In budding yeast Saccharomyces cerevisiae, a condensin complex consists of five subunits: two conserved structural maintenance of chromosome subunits, Smc2 and Smc4, a kleisin Brn1, and two HEAT repeat subunits, Ycg1, which possesses a DNA binding activity, and Ycs4, which can transiently associate with Smc4 and thereby disrupt its association with the Smc2 head. We characterized here DNA binding activity of the non-SMC subunits using an agnostic, model-independent approach. To this end, we mapped the DNA interface of the complex using sulfo-NHS biotin labeling. Besides the known site on Ycg1, we found a patch of lysines at the C-terminal domain of Ycs4 that were protected from biotinylation in the presence of DNA. Point mutations at the predicted protein-DNA interface reduced both Ycs4 binding to DNA and the DNA stimulated ATPase activity of the reconstituted condensin, whereas overproduction of the mutant Ycs4 was detrimental for yeast viability. Notably, the DNA binding site on Ycs4 partially overlapped with its interface with SMC4, revealing an intricate interplay between DNA binding, engagement of the Smc2-Smc4 heads, and ATP hydrolysis and suggesting a mechanism for ATP-modulated loading and translocation of condensins on DNA.

Tissue factor cytoplasmic domain exacerbates post-infarct left ventricular remodeling via orchestrating cardiac inflammation and angiogenesis.

The coagulation protein tissue factor (TF) regulates inflammation and angiogenesis via its cytoplasmic domain in infection, cancer and diabetes. While TF is highly abundant in the heart and is implicated in cardiac pathology, the contribution of its cytoplasmic domain to post-infarct myocardial injury and adverse left ventricular (LV) remodeling remains unknown. Methods: Myocardial infarction was induced in wild-type mice or mice lacking the TF cytoplasmic domain (TF∆CT) by occlusion of the left anterior descending coronary artery. Heart function was monitored with echocardiography. Heart tissue was collected at different time-points for histological, molecular and flow cytometry analysis. Results: Compared with wild-type mice, TF∆CT had a higher survival rate during a 28-day follow-up after myocardial infarction. Among surviving mice, TF∆CT mice had better cardiac function and less LV remodeling than wild-type mice. The overall improvement of post-infarct cardiac performance in TF∆CT mice, as revealed by speckle-tracking strain analysis, was attributed to reduced myocardial deformation in the peri-infarct region. Histological analysis demonstrated that TF∆CT hearts had in the infarct area greater proliferation of myofibroblasts and better scar formation. Compared with wild-type hearts, infarcted TF∆CT hearts showed less infiltration of proinflammatory cells with concomitant lower expression of protease-activated receptor-1 (PAR1) - Rac1 axis. In particular, infarcted TF∆CT hearts displayed markedly lower ratios of inflammatory M1 macrophages and reparative M2 macrophages (M1/M2). In vitro experiment with primary macrophages demonstrated that deletion of the TF cytoplasmic domain inhibited macrophage polarization toward the M1 phenotype. Furthermore, infarcted TF∆CT hearts presented markedly higher peri-infarct vessel density associated with enhanced endothelial cell proliferation and higher expression of PAR2 and PAR2-associated pro-angiogenic pathway factors. Finally, the overall cardioprotective effects observed in TF∆CT mice could be abolished by subcutaneously infusing a cocktail of PAR1-activating peptide and PAR2-inhibiting peptide via osmotic minipumps. Conclusions: Our findings demonstrate that the TF cytoplasmic domain exacerbates post-infarct cardiac injury and adverse LV remodeling via differential regulation of inflammation and angiogenesis. Targeted inhibition of the TF cytoplasmic domain-mediated intracellular signaling may ameliorate post-infarct LV remodeling without perturbing coagulation.

Glycine-Rich Peptides from FUS Have an Intrinsic Ability to Self-Assemble into Fibers and Networked Fibrils.

Glycine-rich regions feature prominently in intrinsically disordered regions (IDRs) of proteins that drive phase separation and the regulated formation of membraneless biomolecular condensates. Interestingly, the Gly-rich IDRs seldom feature poly-Gly tracts. The protein fused in sarcoma (FUS) is an exception. This protein includes two 10-residue poly-Gly tracts within the prion-like domain (PLD) and at the interface between the PLD and the RNA binding domain. Poly-Gly tracts are known to be highly insoluble, being potent drivers of self-assembly into solid-like fibrils. Given that the internal concentrations of FUS and FUS-like molecules cross the high micromolar and even millimolar range within condensates, we reasoned that the intrinsic insolubility of poly-Gly tracts might be germane to emergent fluid-to-solid transitions within condensates. To assess this possibility, we characterized the concentration-dependent self-assembly for three non-overlapping 25-residue Gly-rich peptides derived from FUS. Two of the three peptides feature 10-residue poly-Gly tracts. These peptides form either long fibrils based on twisted ribbon-like structures or self-supporting gels based on physical cross-links of fibrils. Conversely, the peptide with similar Gly contents but lacking a poly-Gly tract does not form fibrils or gels. Instead, it remains soluble across a wide range of concentrations. Our findings highlight the ability of poly-Gly tracts within IDRs that drive phase separation to undergo self-assembly. We propose that these tracts are likely to contribute to nucleation of fibrillar solids within dense condensates formed by FUS.

Developmentally regulated GTPases: structure, function and roles in disease.

GTPases are a large superfamily of evolutionarily conserved proteins involved in a variety of fundamental cellular processes. The developmentally regulated GTP-binding protein (DRG) subfamily of GTPases consists of two highly conserved paralogs, DRG1 and DRG2, both of which have been implicated in the regulation of cell proliferation, translation and microtubules. Furthermore, DRG1 and 2 proteins both have a conserved binding partner, DRG family regulatory protein 1 and 2 (DFRP1 and DFRP2), respectively, that prevents them from being degraded. Similar to DRGs, the DFRP proteins have also been studied in the context of cell growth control and translation. Despite these proteins having been implicated in several fundamental cellular processes they remain relatively poorly characterized, however. In this review, we provide an overview of the structural biology and biochemistry of DRG GTPases and discuss current understanding of DRGs and DFRPs in normal physiology, as well as their emerging roles in diseases such as cancer.

Formation of self-organizing functionally distinct Rho of plants domains involves a reduced mobile population.

Rho family proteins are central to the regulation of cell polarity in eukaryotes. Rho of Plants-Guanyl nucleotide Exchange Factor (ROPGEF) can form self-organizing polar domains following co-expression with an Rho of Plants (ROP) and an ROP GTPase-Activating Protein (ROPGAP). Localization of ROPs in these domains has not been demonstrated, and the mechanisms underlying domain formation and function are not well understood. Here we show that six different ROPs form self-organizing domains when co-expressed with ROPGEF3 and GAP1 in Nicotiana benthamiana or Arabidopsis (Arabidopsis thaliana). Domain formation was associated with ROP-ROPGEF3 association, reduced ROP mobility, as revealed by time-lapse imaging and Fluorescence Recovery After Photobleaching beam size analysis, and was independent of Rho GTP Dissociation Inhibitor mediated recycling. The domain formation depended on the ROPs' activation/inactivation cycles and interaction with anionic lipids via a C-terminal polybasic domain. Coexpression with the microtubule-associated protein ROP effector INTERACTOR OF CONSTITUTIVELY ACTIVE ROP 1 (ICR1) revealed differential function of the ROP domains in the ability to recruit ICR1. Taken together, the results reveal mechanisms underlying self-organizing ROP domain formation and function.

Comparative analysis of the MyTH4-FERM myosins reveals insights into the determinants of actin track selection in polarized epithelia.

MyTH4-FERM (MF) myosins evolved to play a role in the creation and function of a variety of actin-based membrane protrusions that extend from cells. Here we performed an analysis of the MF myosins, Myo7A, Myo7B, and Myo10, to gain insight into how they select for their preferred actin networks. Using enterocytes that create spatially separated actin tracks in the form of apical microvilli and basal filopodia, we show that actin track selection is principally guided by the mode of oligomerization of the myosin along with the identity of the motor domain, with little influence from the specific composition of the lever arm. Chimeric variants of Myo7A and Myo7B fused to a leucine zipper parallel dimerization sequence in place of their native tails both selected apical microvilli as their tracks, while a truncated Myo10 used its native antiparallel coiled-coil to traffic to the tips of filopodia. Swapping lever arms between the Class 7 and 10 myosins did not change actin track preference. Surprisingly, fusing the motor-neck region of Myo10 to a leucine zipper or oligomerization sequences derived from the Myo7A and Myo7B cargo proteins USH1G and ANKS4B, respectively, re-encoded the actin track usage of Myo10 to apical microvilli with significant efficiency.

Dynamics of SARS-CoV-2 Spike Proteins in Cell Entry: Control Elements in the Amino-Terminal Domains.

Selective pressures drive adaptive changes in the coronavirus spike proteins directing virus-cell entry. These changes are concentrated in the amino-terminal domains (NTDs) and the receptor-binding domains (RBDs) of complex modular spike protein trimers. The impact of this hypervariability on virus entry is often unclear, particularly with respect to sarbecovirus NTD variations. Therefore, we constructed indels and substitutions within hypervariable NTD regions and used severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus-like particles and quantitative virus-cell entry assays to elucidate spike structures controlling this initial infection stage. We identified NTD variations that increased SARS-CoV-2 spike protein-mediated membrane fusion and cell entry. Increased cell entry correlated with greater presentation of RBDs to ACE2 receptors. This revealed a significant allosteric effect, in that changes within the NTDs can orient RBDs for effective virus-cell binding. Yet, those NTD changes elevating receptor binding and membrane fusion also reduced interdomain associations, leaving spikes on virus-like particles susceptible to irreversible inactivation. These findings parallel those obtained decades ago, in which comparisons of murine coronavirus spike protein variants established inverse relationships between membrane fusion potential and virus stability. Considerable hypervariability in the SARS-CoV-2 spike protein NTDs also appear to be driven by counterbalancing pressures for effective virus-cell entry and durable extracellular virus infectivity. These forces may selectively amplify SARS-CoV-2 variants of concern. IMPORTANCE Adaptive changes that increase SARS-CoV-2 transmissibility may expand and prolong the coronavirus disease 2019 (COVID-19) pandemic. Transmission requires metastable and dynamic spike proteins that bind viruses to cells and catalyze virus-cell membrane fusion. Using newly developed assays reflecting these two essential steps in virus-cell entry, we focused on adaptive changes in SARS-CoV-2 spike proteins and found that deletions in amino-terminal domains reset spike protein metastability, rendering viruses less stable yet more poised to respond to cellular factors that prompt entry and subsequent infection. The results identify adjustable control features that balance extracellular virus stability with facile virus dynamics during cell entry. These equilibrating elements warrant attention when monitoring the evolution of pandemic coronaviruses.

A protocol for analyzing the protein terminome of human cancer cell line culture supernatants.

Characterization of protein termini is essential for understanding how the proteome is generated through biological processes such as post-translational proteolytic events. Here, we introduce a practical protocol for terminomics to achieve simple and sensitive N- and C-terminal peptide enrichment. We apply it to the terminome analysis of culture supernatants of a human cancer cell line for the purpose of identifying ectodomain shedding substrate cleavage sites with 10 µg protein per sample. For complete details on the use and execution of this protocol, please refer to Tsumagari et al. (2021).

HIV-1 matrix-tRNA complex structure reveals basis for host control of Gag localization.

The HIV-1 virion structural polyprotein, Gag, is directed to particle assembly sites at the plasma membrane by its N-terminal matrix (MA) domain. MA also binds to host tRNAs. To understand the molecular basis of MA-tRNA interaction and its potential function, we present a co-crystal structure of HIV-1 MA-tRNALys3 complex. The structure reveals a specialized group of MA basic and aromatic residues preconfigured to recognize the distinctive structure of the tRNA elbow. Mutational, cross-linking, fluorescence, and NMR analyses show that the crystallographically defined interface drives MA-tRNA binding in solution and living cells. The structure indicates that MA is unlikely to bind tRNA and membrane simultaneously. Accordingly, single-amino-acid substitutions that abolish MA-tRNA binding caused striking redistribution of Gag to the plasma membrane and reduced HIV-1 replication. Thus, HIV-1 exploits host tRNAs to occlude a membrane localization signal and control the subcellular distribution of its major structural protein.

Biological Functions of the Intrinsically Disordered N-Terminal Domain of the Prion Protein: A Possible Role of Liquid-Liquid Phase Separation.

The mammalian prion protein (PrPC) is composed of a large intrinsically disordered N-terminal and a structured C-terminal domain, containing three alpha-helical regions and a short, two-stranded beta-sheet. Traditionally, the activity of a protein was linked to the ability of the polypeptide chain to adopt a stable secondary/tertiary structure. This concept has been extended when it became evident that intrinsically disordered domains (IDDs) can participate in a broad range of defined physiological activities and play a major functional role in several protein classes including transcription factors, scaffold proteins, and signaling molecules. This ability of IDDs to engage in a variety of supramolecular complexes may explain the large number of PrPC-interacting proteins described. Here, we summarize diverse physiological and pathophysiological activities that have been described for the unstructured N-terminal domain of PrPC. In particular, we focus on subdomains that have been conserved in evolution.

GPCR Partners as Cancer Driver Genes: Association with PH-Signal Proteins in a Distinctive Signaling Network.

The essential role of G-protein coupled receptors (GPCRs) in tumor growth is recognized, yet a GPCR based drug in cancer is rare. Understanding the molecular path of a tumor driver gene may lead to the design and development of an effective drug. For example, in members of protease-activated receptor (PAR) family (e.g., PAR1 and PAR2), a novel PH-binding motif is allocated as critical for tumor growth. Animal models have indicated the generation of large tumors in the presence of PAR1 or PAR2 oncogenes. These tumors showed effective inhibition when the PH-binding motif was either modified or were inhibited by a specific inhibitor targeted to the PH-binding motif. In the second part of the review we discuss several aspects of some cardinal GPCRs in tumor angiogenesis.