Evolutionary epitopes of Hsp90 and p23: implications for their interaction

Heat shock protein 90: biological functions, diseases, and therapeutic targets

Heat shock protein 90 (Hsp90) is a predominant member among Heat shock proteins (HSPs), playing a central role in cellular protection and maintenance by aiding in the folding, stabilization, and modification of diverse protein substrates. It collaborates with various co-chaperones to manage ATPase-driven conformational changes in its dimer during client protein processing. Hsp90 is critical in cellular function, supporting the proper operation of numerous proteins, many of which are linked to diseases such as cancer, Alzheimer's, neurodegenerative conditions, and infectious diseases. Recognizing the significance of these client proteins across diverse diseases, there is a growing interest in targeting Hsp90 and its co-chaperones for potential therapeutic strategies. This review described biological background of HSPs and the structural characteristics of HSP90. Additionally, it discusses the regulatory role of heat shock factor-1 (HSF-1) in modulating HSP90 and sheds light on the dynamic chaperone cycle of HSP90. Furthermore, the review discusses the specific contributions of HSP90 in various disease contexts, especially in cancer. It also summarizes HSP90 inhibitors for cancer treatment, offering a thoughtful analysis of their strengths and limitations. These advancements in research expand our understanding of HSP90 and open up new avenues for considering HSP90 as a promising target for therapeutic intervention in a range of diseases.

Heat Shock Protein 90 in Parkinson's Disease: Profile of a Serial Killer

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by abnormal α-synuclein misfolding and aggregation, mitochondrial dysfunction, oxidative stress, as well as progressive death of dopaminergic neurons in the substantia nigra. Molecular chaperones play a role in stabilizing proteins and helping them achieve their proper structure. Previous studies have shown that overexpression of heat shock protein 90 (HSP90) can lead to the death of dopaminergic neurons associated with PD. Inhibiting HSP90 is considered a potential treatment approach for neurodegenerative disorders, as it may reduce protein aggregation and related toxicity, as well as suppress various forms of regulated cell death (RCD). This review provides an overview of HSP90 and its role in PD, focusing on its modulation of proteostasis and quality control of LRRK2. The review also explores the effects of HSP90 on different types of RCD, such as apoptosis, chaperone-mediated autophagy (CMA), necroptosis, and ferroptosis. Additionally, it discusses HSP90 inhibitors that have been tested in PD models. We will highlight the under-investigated neuroprotective effects of HSP90 inhibition, including modulation of oxidative stress, mitochondrial dysfunction, PINK/PARKIN, heat shock factor 1 (HSF1), histone deacetylase 6 (HDAC6), and the PHD2-HSP90 complex-mediated mitochondrial stress pathway. By examining previous literature, this review uncovers overlooked neuroprotective mechanisms and emphasizes the need for further research on HSP90 inhibitors as potential therapeutic strategies for PD. Finally, the review discusses the potential limitations and possibilities of using HSP90 inhibitors in PD therapy.

Structural elements in the flexible tail of the co-chaperone p23 coordinate client binding and progression of the Hsp90 chaperone cycle

The co-chaperone p23 is a central part of the Hsp90 machinery. It stabilizes the closed conformation of Hsp90, inhibits its ATPase and is important for client maturation. Yet, how this is achieved has remained enigmatic. Here, we show that a tryptophan residue in the proximal region of the tail decelerates the ATPase by allosterically switching the conformation of the catalytic loop in Hsp90. We further show by NMR spectroscopy that the tail interacts with the Hsp90 client binding site via a conserved helix. This helical motif in the p23 tail also binds to the client protein glucocorticoid receptor (GR) in the free and Hsp90-bound form. In vivo experiments confirm the physiological importance of ATPase modulation and the role of the evolutionary conserved helical motif for GR activation in the cellular context.

Targeting chaperones, heat shock factor-1, and unfolded protein response: Promising therapeutic approaches for neurodegenerative disorders

Protein misfolding, which is known to cause several serious diseases, is an emerging field that addresses multiple therapeutic areas. Misfolding of a disease-specific protein in the central nervous system ultimately results in the formation of toxic aggregates that may accumulate in the brain, leading to neuronal cell death and dysfunction, and associated clinical manifestations. A large number of neurodegenerative diseases in humans, including Alzheimer's, Parkinson's, Huntington's, and prion diseases, are primarily caused by protein misfolding and aggregation. Notably, the cellular system is equipped with a protein quality control system encompassing chaperones, ubiquitin proteasome system, and autophagy, as a defense mechanism that monitors protein folding and eliminates inappropriately folded proteins. As the intrinsic molecular mechanisms of protein misfolding become more clearly understood, the novel therapeutic approaches in this arena are gaining considerable interest. The present review will describe the chaperones network and different approaches as the therapeutic targets for neurodegenerative diseases. Current and emerging therapeutic approaches to combat neurodegenerative diseases, addressing the roles of molecular, chemical, and pharmacological chaperones, as well as heat shock factor-1 and the unfolded protein response, are also discussed in detail.

p23 and Aha1

Hsp90 is a conserved molecular chaperone and is responsible for the folding and activation of several hundred client proteins, involved in various cellular processes. The large number and the diversity of these client proteins demand a high adaptiveness of Hsp90 towards the need of the individual client. This adaptiveness is amongst others mediated by more than 20 so-called cochaperones that differ in their actions towards Hsp90. Some of these cochaperones are able to modulate the ATPase activity of Hsp90 and/or its client protein binding, folding and activation. p23 and Aha1 are two prominent examples with opposing effects on the ATPase activity of Hsp90. p23 is able to inhibit the ATP turnover while Aha1 is the strongest known activator of the ATPase activity of Hsp90. Even though both cochaperones are conserved from yeast to man and have been studied for years, some Hsp90-related as well as Hsp90-independent functions are still enigmatic and under current investigation. In this chapter, we first introduce the ATPase cycle of Hsp90 and then focus on the two cochaperones integrating them in the Hsp90 cycle.

The co-chaperone p23 promotes prostate cancer motility and metastasis

Prostate cancer is an androgen receptor (AR)‐dependent malignancy at initiation and progression, therefore hormone therapy is the primary line of systemic treatment. Despite initial disease regression, tumours inevitably recur and progress to an advanced castration‐resistant state a major feature of which is metastasis to the bone. Up‐regulation of AR cofactors and chaperones that overcome low hormone conditions to maintain basal AR activity has been postulated as a mechanism of therapy relapse.

p23, an essential component of the apo‐AR complex, acts also after ligand binding to increase AR transcriptional activity and target gene expression, partly by increasing chromatin‐loaded holo‐receptor‐complexes. Immunohistochemical studies have demonstrated increased p23 expression in advanced prostate cancer. Here, we further characterise p23 roles in AR signalling and show that it modulates cytosolic AR levels in the absence of hormone, confirming a chaperoning function in the aporeceptor complex and suggesting p23 upregulates AR signalling at multiple stages. Moreover, p23 protein levels significantly increased upon treatment with not only androgen but also clinically relevant anti‐androgens. This was in contrast to the HSP90 inhibitor 17‐AAG, which did not modulate expression of the cochaperone – important given the HSP90‐independent roles we and others have previously described for p23.

Further, we demonstrate p23 is implicated in prostate cancer cell motility and in acquisition of invasiveness capacity through the expression of specific genes known to participate in cancer progression. This may drive metastatic processes in vivo since analysis of prostate tumour biopsies revealed that high nuclear p23 significantly correlated with shorter survival times and with development of metastases in patients with lower grade tumours. We propose that increased p23 expression may allow cells to acquire a more aggressive phenotype, contributing to disease progression, and that p23 is a plausible secondary target in combination with HSP90 inhibition as a potential therapy for advanced prostate cancer.

We report a novel function for p23 in prostate cancer progression.

p23 protein levels increase upon treatment with androgens and anti‐androgens.

p23 promotes prostate cancer cell motility and acquisition of invasiveness.

High nuclear p23 significantly correlates with shorter survival times in patients.

p23 may reprogram gene expression profile into a more metastatic pattern.

Towards establishment of a rice stress response interactome

Rice (Oryza sativa) is a staple food for more than half the world and a model for studies of monocotyledonous species, which include cereal crops and candidate bioenergy grasses. A major limitation of crop production is imposed by a suite of abiotic and biotic stresses resulting in 30%-60% yield losses globally each year. To elucidate stress response signaling networks, we constructed an interactome of 100 proteins by yeast two-hybrid (Y2H) assays around key regulators of the rice biotic and abiotic stress responses. We validated the interactome using protein-protein interaction (PPI) assays, co-expression of transcripts, and phenotypic analyses. Using this interactome-guided prediction and phenotype validation, we identified ten novel regulators of stress tolerance, including two from protein classes not previously known to function in stress responses. Several lines of evidence support cross-talk between biotic and abiotic stress responses. The combination of focused interactome and systems analyses described here represents significant progress toward elucidating the molecular basis of traits of agronomic importance.

The Hsp90 co-chaperone p23 of Toxoplasma gondii: Identification, functional analysis and dynamic interactome determination

Toxoplasma gondii is among the most successful parasites, with nearly half of the human population chronically infected. Recently a link between the T. gondii Hsp90 chaperone machinery and parasite development was observed. Here, the T. gondii Hsp90 co-chaperones p23 and Hip were identified mining the Toxoplasma- database (www.toxodb.org). Their identity was confirmed by domain structure and blast analysis. Additionally, analysis of the secondary structure and studies on the chaperone function of the purified protein verified the p23 identity. Studies of co-immunoprecipitation (co-IP) identified two different types of complexes, one comprising at least Hip-Hsp70-Hsp90 and another containing at least p23-Hsp90. Indirect immunofluorescence assays showed that Hip is localized in the cytoplasm in tachyzoites and as well in bradyzoites. For p23 in contrast, a solely cytoplasmic localization was only observed in the tachyzoite stage whereas nuclear and cytosolic distribution and co-localization with Hsp90 was observed in bradyzoites. These results indicate that the T. gondii Hsp90-heterocomplex cycle is similar to the one proposed for higher eukaryotes, further highlighting the implication of the Hsp90/p23 in parasite development. Furthermore, co-IP experiments of tachyzoite/bradyzoite lysates with anti-p23 antiserum and identification of the complexed proteins together with the use of the curated interaction data available from different source (orthologs and Plasmodium databases) allowed us to construct an interaction network (interactome) covering the dynamics of the Hsp90 chaperone machinery.

Understanding the molecular basis of plant growth promotional effect of Pseudomonas fluorescens on rice through protein profiling

BACKGROUND

Plant Growth Promoting Rhizobacteria (PGPR), Pseudomonas fluorescens strain KH-1 was found to exhibit plant growth promotional activity in rice under both in-vitro and in-vivo conditions. But the mechanism underlying such promotional activity of P. fluorescens is not yet understood clearly. In this study, efforts were made to elucidate the molecular responses of rice plants to P. fluorescens treatment through protein profiling. Two-dimensional polyacrylamide gel electrophoresis strategy was adopted to identify the PGPR responsive proteins and the differentially expressed proteins were analyzed by mass spectrometry.

RESULTS

Priming of P. fluorescens, 23 different proteins found to be differentially expressed in rice leaf sheaths and MS analysis revealed the differential expression of some important proteins namely putative p23 co-chaperone, Thioredoxin h- rice, Ribulose-bisphosphate carboxylase large chain precursor, Nucleotide diPhosphate kinase, Proteosome sub unit protein and putative glutathione S-transferase protein.

CONCLUSION

Functional analyses of the differential proteins were reported to be directly or indirectly involved in growth promotion in plants. Thus, this study confirms the primary role of PGPR strain KH-1 in rice plant growth promotion.

Structure and functional studies of the CS domain of the essential H/ACA ribonucleoparticle assembly protein SHQ1

H/ACA ribonucleoprotein particles are essential for ribosomal RNA and telomerase RNA processing and metabolism. Shq1p has been identified as an essential eukaryotic H/ACA small nucleolar (sno) ribonucleoparticle (snoRNP) biogenesis and assembly factor. Shq1p is postulated to be involved in the early biogenesis steps of H/ACA snoRNP complexes, and Shq1p depletion leads to a specific decrease in H/ACA small nucleolar RNA levels and to defects in ribosomal RNA processing. Shq1p contains two predicted domains as follows: an N-terminal CS (named after CHORD-containing proteins and SGT1) or HSP20-like domain, and a C-terminal region of high sequence homology called the Shq1 domain. Here we report the crystal structure and functional studies of the Saccharomyces cerevisiae Shq1p CS domain. The structure consists of a compact anti-parallel beta-sandwich fold that is composed of two beta-sheets containing four and three beta-strands, respectively, and a short alpha-helix. Deletion studies showed that the CS domain is required for the essential functions of Shq1p. Point mutations in residues Phe-6, Gln-10, and Lys-80 destabilize Shq1p in vivo and induce a temperature-sensitive phenotype with depletion of H/ACA small nucleolar RNAs and defects in rRNA processing. Although CS domains are frequently found in co-chaperones of the Hsp90 molecular chaperone, no interaction was detected between the Shq1p CS domain and yeast Hsp90 in vitro. These results show that the CS domain is essential for Shq1p function in H/ACA snoRNP biogenesis in vivo, possibly in an Hsp90-independent manner.

The microtubule-associated protein, NUD-1, exhibits chaperone activity in vitro

Regulation of cell division requires the concerted function of proteins and protein complexes that properly mediate cytoskeletal dynamics. NudC is an evolutionarily conserved protein of undetermined function that associates with microtubules and interacts with several key regulators of mitosis, such as polo-kinase 1 (Plk1) and dynein. NudC is essential for proper mitotic progression, and homologs have been identified in species ranging from fungi to humans. In this paper, we report the characterization of the Caenorhabditis elegans NudC homolog, NUD-1, as a protein exhibiting molecular chaperone activity. All NudC/NUD-1 proteins share a conserved p23/HSP20 domain predicted by three-dimensional modeling [Garcia-Ranea, Mirey, Camonis, Valencia, FEBS Lett 529(2-3):162-167, 2002]. We demonstrate that nematode NUD-1 is able to prevent the aggregation of two substrate proteins, citrate synthase (CS) and luciferase, at stoichiometric concentrations. Further, NUD-1 also protects the native state of CS from thermal inactivation by significantly reducing the inactivation rate of this enzyme. To further determine if NUD-1/substrate complexes were productive or simply "dead-end" unfolding intermediates, a luciferase refolding assay was utilized. Following thermal denaturation, rabbit reticulocyte lysate and ATP were added and luciferase activity measured. In the presence of NUD-1, nearly all of the luciferase activity was regained, indicating that unfolded intermediates complexed with NUD-1 could be refolded. These studies represent the first functional evidence for a member of this mitotically essential protein family as having chaperone activity and facilitates elucidation of the role such proteins play in chaperone complexes utilized in cell division. C. elegans NUD-1 is a member of an evolutionary conserved protein family of unknown function involved in the regulation of cytoskeletal dynamics. NUD-1 and its mammalian homolog, NudC, function with the dynein motor complex to ensure proper cell division, and knockdown or overexpression of these proteins leads to disruption of mitosis. In this paper, we show that NUD-1 possesses ATP-independent chaperone activity comparable to that of small heat shock proteins and cochaperones and that changes in phosphorylation state functionally alter chaperone activity in a phosphomimetic NUD-1 mutant.

Coupling endoplasmic reticulum stress to the cell death program in dopaminergic cells: effect of paraquat

Parkinson's disease (PD) features oxidative stress and accumulation of misfolded (unfolded, alternatively folded, or mutant) proteins with associated loss of dopaminergic neurons. Oxidative stress and the accumulated misfolded proteins elicit cellular responses that include an endoplasmic reticulum (ER) stress response that may protect cells against the toxic buildup of misfolded proteins. Chronic ER stress and accumulation of misfolded proteins in excessive amounts, however, overwhelm the cellular 'quality control' system and impair the protective mechanisms designed to promote correct folding and degrade faulty proteins, ultimately leading to organelle dysfunction and neuronal cell death. Paraquat belongs to a class of bipyridyl herbicides and triggers oxidative stress and dopaminergic cell death. Epidemiological studies suggest an increased risk for developing PD following chronic exposure to paraquat. The present study was carried out to determine the role of paraquat in triggering cellular stress particularly ER stress and to elucidate the pathways that couple ER stress to dopaminergic cell death. We demonstrate that paraquat triggers ER stress, cell dysfunction, and dopaminergic cell death. p23, a small co-chaperone protein, is cleaved during ER stress-induced cell death triggered by paraquat and blockage of the caspase cleavage site of p23 was associated with decreased cell death. Paraquat also inhibits proteasomal activity that may further trigger accumulation of misfolded proteins resulting in ER stress. Our results indicate a protective role for p23 in PD-related programmed cell death. The data also underscore the involvement of ER, caspases, and the proteasomal system in ER stress-induced cell death process.

Activation of cathepsin L by the cathelin-like domain of protegrin-3

The cathelin-like domain (CLD) of the antimicrobial cathelicidin family constitutes a unique protein family with structural similarity to cystatins, the cysteine protease inhibitors. CLDs are derived from the processed amino-terminal prosequence of the cathelicidin precursors with conservation across the vertebrate lineage ranging from fish to human. Initial attempt to characterize a possible inhibitory activity of protegrin-3 (PG3) CLD protein (a member of the multigene family of porcine cathelicidins) against several proteases led to an unexpected finding that PG3 CLD efficiently activated rather than inhibited human cathepsin L. Partial deletion of the L2 loop of PG3 CLD, a structurally equivalent region important in interaction of cystatins with proteases, significantly decreased its activating effect on cathepsin L. A complex model based on this functional loop was proposed to explain this unexpected effect, in which evolutionary emergence of completely opposite biological activity could be associated with structural discrepancies of the loop due to sequence variations between pig and human. Our results provide new insights into deeper understanding of the immune-related biological activity of this so-called pro-domain of the cathelicidin family.

A postgenomic view of the heat shock proteins in kinetoplastids

The kinetoplastids Leishmania major, Trypanosoma brucei and Trypanosoma cruzi are causative agents of a diverse spectrum of human diseases: leishmaniasis, sleeping sickness and Chagas' disease, respectively. These protozoa possess digenetic life cycles that involve development in mammalian and insect hosts. It is generally accepted that temperature is a triggering factor of the developmental programme allowing the adaptation of the parasite to the mammalian conditions. The heat shock response is a general homeostatic mechanism that protects cells from the deleterious effects of environmental stresses, such as heat. This response is universal and includes the synthesis of the heat-shock proteins (HSPs). In this review, we summarize the salient features of the different HSP families and describe their main cellular functions. In parallel, we analyse the composition of these families in kinetoplastids according to literature data and our understanding of genome sequence data. The genome sequences of these parasites have been recently completed. The HSP families described here are: HSP110, HSP104, group I chaperonins, HSP90, HSP70, HSP40 and small HSPs. All these families are widely represented in these parasites. In particular, kinetoplastids possess an unprecedented number of members of the HSP70, HSP60 and HSP40 families, suggesting key roles for these HSPs in their biology.

WHISCY: what information does surface conservation yield? Application to data-driven docking

Protein-protein interactions play a key role in biological processes. Identifying the interacting residues is a first step toward understanding these interactions at a structural level. In this study, the interface prediction program WHISCY is presented. It combines surface conservation and structural information to predict protein-protein interfaces. The accuracy of the predictions is more than three times higher than a random prediction. These predictions have been combined with another interface prediction program, ProMate [Neuvirth et al. J Mol Biol 2004;338:181-199], resulting in an even more accurate predictor. The usefulness of the predictions was tested using the data-driven docking program HADDOCK [Dominguez et al. J Am Chem Soc 2003;125:1731-1737] in an unbound docking experiment, with the goal of generating as many near-native structures as possible. Unrefined rigid body docking solutions within 10 A ligand RMSD from the true structure were generated for 22 out of 25 docked complexes. For 18 complexes, more than 100 of the 8000 generated models were correct. Our results demonstrates the potential of using interface predictions to drive protein-protein docking.

A Salmonella type III secretion effector interacts with the mammalian serine/threonine protein kinase PKN1

Essential to salmonellae pathogenesis is an export device called the type III secretion system (TTSS), which mediates the transfer of bacterial effector proteins from the bacterial cell into the host cell cytoplasm. Once inside the host cell, these effectors are then capable of altering a variety of host cellular functions in order to promote bacterial survival and colonization. SspH1 is a Salmonella enterica serovar Typhimurium TTSS effector that localizes to the mammalian nucleus and down-modulates production of proinflammatory cytokines by inhibiting nuclear factor (NF)-kappaB-dependent gene expression. To identify mammalian binding partners of SspH1 a yeast two-hybrid screen against a human spleen cDNA library was performed. It yielded a serine/threonine protein kinase called protein kinase N 1 (PKN1). The leucine-rich repeat domain of SspH1 was demonstrated to mediate this interaction and also inhibition of NF-kappaB-dependent gene expression. This suggested that PKN1 may play a role in modulation of the NF-kappaB signalling pathway. Indeed, we found that expression of constitutively active PKN1 in mammalian cells results in a decrease, while depletion of PKN1 by RNA interference causes an increase in NF-kappaB-dependent reporter gene expression. These data indicate that SspH1 may inhibit the host's inflammatory response by interacting with PKN1.

Stress by heat shock induces massive down regulation of genes and allows differential allelic expression of the Gal/GalNAc lectin in Entamoeba histolytica

Gene expression analysis by microarray assay revealed that when exposed to stress, Entamoeba histolytica exhibits a specific heat shock response, together with a dramatic overall reduction in gene transcription as well as differential allelic expression of key genes participating in virulence, such as the galactose/N-acetylgalactosamine (Gal/GalNAc) lectin.

Characterization and expression of p23 gene in the amphioxus Branchiostoma belcheri

The cDNA AmphiP23, encoding an amphioxus p23, was identified from the gut cDNA library of amphioxus Branchiostoma belcheri. It contains a 513 bp open reading frame corresponding to a deduced protein of 170 amino acids. Phylogenetic analysis shows that vertebrate and invertebrate p23/p23-like proteins are each grouped together, with AmphiP23 falling at the base of vertebrate p23/p23-like clade, suggesting that the divergence of vertebrate and invertebrate p23 genes probably occurs prior to the split of invertebrate/vertebrate from a common ancestor around 550 million years ago. Northern blotting reveals a ubiquitous expression pattern of AmphiP23 in all adult tissues examined, while whole mount in situ hybridization demonstrates a tissue- and stage-specific expression pattern of AmphiP23 in developing embryos and larvae. Presumably, the ubiquitous expression pattern of AmphiP23 in adult amphioxus represents the ancestral type of p23 gene prior to its split to human paralogs p23 and tsp23, while the tissue- and stage-specific expression pattern during early embryonic development implicates a role of AmphiP23 in anterior/posterior patterning.

Coupling endoplasmic reticulum stress to the cell-death program: a novel HSP90-independent role for the small chaperone protein p23

The endoplasmic reticulum (ER) is the principal organelle for the biosynthesis of proteins, steroids and many lipids, and is highly sensitive to alterations in its environment. Perturbation of Ca(2+) homeostasis, elevated secretory protein synthesis, deprivation of glucose or other sugars, altered glycosylation and/or the accumulation of misfolded proteins may all result in ER stress, and prolonged ER stress triggers cell death. Studies from multiple laboratories have identified the roles of several ER stress-induced cell-death modulators and effectors through the use of biochemical, pharmacological and genetic tools. In the present work, we describe the role of p23, a small chaperone protein, in preventing ER stress-induced cell death. p23 is a highly conserved chaperone protein that modulates HSP90 activity and is also a component of the steroid receptors. p23 is cleaved during ER stress-induced cell death; this cleavage, which occurs close to the carboxy-terminus, requires caspase-3 and/or caspase-7, but not caspase-8. Blockage of the caspase cleavage site of p23 was associated with decreased cell death induced by ER stress. Immunodepletion of p23 or inhibition of p23 expression by siRNA resulted in enhancement of ER stress-induced cell death. While p23 co-immunoprecipitated with the BH3-only protein PUMA (p53-upregulated modulator of apoptosis) in untreated cells, prolonged ER stress disrupted this interaction. The results define a protective role for p23, and provide further support for a model in which ER stress is coupled to the mitochondrial intrinsic apoptotic pathway through the activities of BH3 family proteins.

Neuronal responses to myelin are mediated by rho kinase

CNS myelin inhibits axon growth due to the expression of several growth-inhibitory proteins, including myelin-associated glycoprotein, oligodendrocyte myelin glycoprotein and Nogo. Myelin-associated inhibitory proteins activate rho GTPase in responsive neurons. Rho kinase (ROCK) has been implicated as a critical rho effector in this pathway due to the ability of the pharmacological inhibitor Y-27632 to circumvent myelin-dependent inhibition. Y-27632, however, inhibits the activity of additional kinases. Using three independent approaches, we provide direct evidence that ROCKII is activated in response to the myelin-associated inhibitor Nogo. We demonstrate that Nogo treatment enhances ROCKII translocation to the cellular membrane in PC12 cells and enhances ROCKII kinase activity towards an in vitro substrate. In addition, Nogo treatment enhances phosphorylation of myosin light chain II, a known ROCK substrate. Further, we demonstrate that primary dorsal root ganglia neurons can be rendered insensitive to the inhibitory effects of myelin via infection with dominant negative ROCK. Together these data provide direct evidence for a rho-ROCK-myosin light chain-II signaling cascade in response to myelin-associated inhibitors.

The co-chaperone p23 arrests the Hsp90 ATPase cycle to trap client proteins

The action of the molecular chaperone Hsp90 is essential for the activation and assembly of an increasing number of client proteins. This function of Hsp90 has been proposed to be governed by conformational changes driven by ATP binding and hydrolysis. Association of co-chaperones and client proteins regulate the ATPase activity of Hsp90. Here, we have examined the inhibition of the ATPase activity of human Hsp90beta by one such co-chaperone, human p23. We demonstrate that human p23 interacts with Hsp90 in both the absence and presence of nucleotide with a higher affinity in the presence of the ATP analogue AMP-PNP. This is consistent with an analysis of the effect of p23 on the steady-state kinetics that revealed a mixed mechanism of inhibition. Mass spectrometry of the intact Hsp90.p23 complex determined the stoichiometry of binding to be one p23 to each subunit of the Hsp90 dimer. p23 was also shown to interact with a monomeric, truncated fragment of Hsp90, lacking the C-terminal homodimerisation domain, indicating dimerisation of Hsp90 is not a prerequisite for association with p23. Complex formation between Hsp90 and p23 increased the apparent affinity of Hsp90 for AMP-PNP and completely inhibited the ATPase activity. We propose a model where the role of p23 is to lock individual subunits of Hsp90 in an ATP-dependent conformational state that has a high affinity for client proteins.

Data-driven docking for the study of biomolecular complexes

With the amount of genetic information available, a lot of attention has focused on systems biology, in particular biomolecular interactions. Considering the huge number of such interactions, and their often weak and transient nature, conventional experimental methods such as X-ray crystallography and NMR spectroscopy are not sufficient to gain structural insight into these. A wealth of biochemical and/or biophysical data can, however, readily be obtained for biomolecular complexes. Combining these data with docking (the process of modeling the 3D structure of a complex from its known constituents) should provide valuable structural information and complement the classical structural methods. In this review we discuss and illustrate the various sources of data that can be used to map interactions and their combination with docking methods to generate structural models of the complexes. Finally a perspective on the future of this kind of approach is given.