Complex formation of 70-kDa heat shock protein with acidic glycolipids and phospholipids

Concentrations of HSP27 and αβ-crystallin in Oula Tibetan sheep meat and their relationship with meat quality during postmortem aging

HSP27 and αβ-crystallin are molecular chaperones participating in multiple cellular processes. Their roles in the development of postmortem meat quality remain unclear. The current study was designed to investigate the relationship between the concentrations of HSP27 and αβ-crystallin with meat quality during postmortem aging. Specifically, cooking loss, color, pH, and the myofibril fragmentation index (MFI) of Oula Tibetan sheep meat were determined, and changes in the concentrations of HSP27 and αβ-crystallin were evaluated. The results indicated that HSP27 concentration significantly decreased in 0-3 days (p < 0.05), presenting a positive correlation with pH (p < 0.05) and a negative correlation with L*, b*, cooking loss, and MFI (p < 0.05, p < 0.05, p < 0.01, p < 0.01). Besides, αβ-crystallin concentration significantly decreased in 0-2 days (p < 0.05), exhibiting a significant positive correlation with pH (p < 0.05) and a negative correlation with L*, b*, cooking loss, and MFI (p < 0.01, p < 0.01, p < 0.01, p < 0.01). The results suggested that the HSP27 and αβ-crystallin may participate in the development of meat quality in Oula Tibetan sheep during postmortem early aging. PRACTICAL APPLICATION: Tenderness, color, and water holding capacity (WHC) are crucial quality attributes of meat. The relationship between the concentrations of HSP27 and αβ-crystallin and meat quality reveals that HSP27 and αβ-crystallin may contribute to the development of meat quality in Oula Tibetan sheep during postmortem aging. Therefore, HSP27 and αβ-crystallin are effective research objects for regulating meat quality during postmortem aging.

Hsp70 in cancer: A double agent in the battle between survival and death

The heat shock protein (Hsps) superfamily, also known as molecular chaperones, are highly conserved and present in all living organisms and play vital roles in protein fate. The HspA1A (Hsp70-1), called Hsp70 in this review, is expressed at low or undetectable levels in most unstressed normal cells, but numerous studies have shown that diverse types of tumor cells express Hsp70 at the plasma membrane that leads to resistance to programmed cell death and tumor progression. Hsp70 is released into the extracellular milieu in three forms including free soluble, complexed with cancer antigenic peptides, and exosome forms. Therefore, it seems to be a promising therapeutic target in human malignancies. However, a great number of studies have indicated that both intracellular and extracellular Hsp70 have a dual function. A line of evidence presented that intracellular Hsp70 has a cytoprotective function via suppression of apoptosis and lysosomal cell death (LCD) as well as that extracellular Hsp70 can promote tumorigenesis and angiogenesis. Other evidence showed intracellular Hsp70 can promote apoptosis and membrane-associated/extracellular Hsp70 can elicit antitumor innate and adaptive immune responses. Given the contradictory functions, as a "double agent," could Hsp70 be a promising tool in the future of targeted cancer therapies? To answer this question, in this review, we will discuss the functions of Hsp70 in cancers besides inhibition and stimulation strategies for targeting Hsp70 along with their challenges.

The dynamics and role of sphingolipids in eukaryotic organisms upon thermal adaptation

All living beings have an optimal temperature for growth and survival. With the advancement of global warming, the search for understanding adaptive processes to climate changes has gained prominence. In this context, all living beings monitor the external temperature and develop adaptive responses to thermal variations. These responses ultimately change the functioning of the cell and affect the most diverse structures and processes. One of the first structures to detect thermal variations is the plasma membrane, whose constitution allows triggering of intracellular signals that assist in the response to temperature stress. Although studies on this topic have been conducted, the underlying mechanisms of recognizing thermal changes and modifying cellular functioning to adapt to this condition are not fully understood. Recently, many reports have indicated the participation of sphingolipids (SLs), major components of the plasma membrane, in the regulation of the thermal stress response. SLs can structurally reinforce the membrane or/and send signals intracellularly to control numerous cellular processes, such as apoptosis, cytoskeleton polarization, cell cycle arresting and fungal virulence. In this review, we discuss how SLs synthesis changes during both heat and cold stresses, focusing on fungi, plants, animals and human cells. The role of lysophospholipids is also discussed.

Differential expression of heat shock protein 90, 70, 60 in chicken muscles postmortem and its relationship with meat quality

Objective

The aim of this study was to investigate the expression of heat shock protein (HSP) 90, 70, and 60 in chicken muscles and their possible relationship with quality traits of meat.

Methods

The breast muscles from one hundred broiler chickens were analyzed for drip loss and other quality parameters, and the levels of heat shock protein (HSP) 90, 70, and 60 were determined by immunoblots.

Results

Based on the data, chicken breast muscles were segregated into low (drip loss≤5%), intermediate (5%<drip loss<9.5%) and high (drip loss≥9.5) drip loss groups. The expression of HSP90 and HSP60 were significantly lower in the high drip loss group compared to that in the low and intermediate drip loss group (p<0.05), while HSP70 was equivalent in abundance in all groups (p>0.05).

Conclusion

Results of this study suggests that higher levels of HSP90 and HSP60 may be advantageous for maintenance of cell function and reduction of water loss, and they could act as potential indicator for better water holding capacity of meat.

Characterization of the binding between a 70-kDa heat shock protein, HspA1A, and phosphoinositides

HspA1A, a seventy-kilodalton heat shock protein, binds to specific anionic lipids and this interaction regulates important physiological phenomena like apoptosis, tumor growth, and lysosomal rescue. However, whether HspA1A binds to phosphoinositides has yet to be established and quantified. Therefore, in this study, we determined the binding affinity of HspA1A to several phosphoinositides and characterized five aspects of their molecular interaction. First, we established that HspA1A binds phosphatidylinositol monophosphates with higher affinity than di- and triphosphorylated inositides. Second, using high concentrations of potassium we found that HSPA1A embeds within the lipid bilayer of all phosphoinositides tested. However, the effects of the high salt concentrations were significantly different between the different phosphoinositides. Third, using calcium and reaction buffers equilibrated at different pH values we found that these differentially affected HspA1A-phosphoinositide binding, revealing a lipid-specific pattern of binding. Fourth, by assessing the binding properties of the two HspA1A domains, the nucleotide-binding domain and the substrate-binding domain, we determined that in most cases the full-length protein is necessary for binding to phosphoinositides. Fifth, by including in the reactions nucleotides and protein substrates we determined that they minimally and differentially affected phosphoinositide-binding. Collectively, these findings strongly suggest that the HspA1A-phosphoinositide binding is complex yet specific, is mediated by both electrostatic and hydrophobic interactions, is not related to the lipid-head charge, and depends on the physicochemical properties of the lipid.

Biochemical characterization of the interaction between HspA1A and phospholipids

Seventy-kilodalton heat shock proteins (Hsp70s) are molecular chaperones essential for maintaining cellular homeostasis. Apart from their indispensable roles in protein homeostasis, specific Hsp70s localize at the plasma membrane and bind to specific lipids. The interaction of Hsp70s with lipids has direct physiological outcomes including lysosomal rescue, microautophagy, and promotion of cell apoptosis. Despite these essential functions, the Hsp70-lipid interactions remain largely uncharacterized. In this study, we characterized the interaction of HspA1A, an inducible Hsp70, with five phospholipids. We first used high concentrations of potassium and established that HspA1A embeds in membranes when bound to all anionic lipids tested. Furthermore, we found that protein insertion is enhanced by increasing the saturation level of the lipids. Next, we determined that the nucleotide-binding domain (NBD) of the protein binds to lipids quantitatively more than the substrate-binding domain (SBD). However, for all lipids tested, the full-length protein is necessary for embedding. We also used calcium and reaction buffers equilibrated at different pH values and determined that electrostatic interactions alone may not fully explain the association of HspA1A with lipids. We then determined that lipid binding is inhibited by nucleotide-binding, but it is unaffected by protein-substrate binding. These results suggest that the HspA1A lipid-association is specific, depends on the physicochemical properties of the lipid, and is mediated by multiple molecular forces. These mechanistic details of the Hsp70-lipid interactions establish a framework of possible physiological functions as they relate to chaperone regulation and localization.

HspA1A, a 70-kDa heat shock protein, differentially interacts with anionic lipids

HspA1A, a 70-kDa heat shock protein, binds to specific lipids. This interaction allows HspA1A to associate with the plasma and other cellular membranes, where it regulates many vital functions like immunity, membrane stabilization, autophagy, and apoptosis. However, the molecular mechanism of the HspA1A-lipid interactions has yet to be fully characterized. Therefore, in this study, we characterized the interaction of HspA1A with three lipids, bis-(monoacylglycero)-phosphate, cardiolipin, and sulfatide. Our results revealed that, first, HspA1A embeds in membranes when bound to liposomes composed of cardiolipin and sulfatide. Second, the binding of HspA1A to lipids is complex and although important, electrostatic interactions alone cannot fully explain the observed binding. Third, the two HspA1A domains, the nucleotide-binding domain and the substrate-binding domain, differentially bind to lipids in a lipid-specific manner. Fourth, HspA1A lipid-binding is reduced by the presence of nucleotides, but it is unaffected by the presence of a peptide-substrate. These observations suggest that HspA1A binds to lipids via a multi-step mechanism and this interaction depends on the specific physicochemical properties of the lipid. We speculate that the association of HspA1A with lipids like the mitochondrial cardiolipin, which is an organelle marker, may facilitate the translocation and localized function of the molecular chaperone to particular sub-cellular compartments.

Understanding Early Post-Mortem Biochemical Processes Underlying Meat Color and pH Decline in the Longissimus thoracis Muscle of Young Blond d'Aquitaine Bulls Using Protein Biomarkers

Many studies on color biochemistry and protein biomarkers were undertaken in post-mortem beef muscles after ≥24 hours. The present study was conducted on Longissimus thoracis muscles of 21 Blond d'Aquitaine young bulls to evaluate the relationships between protein biomarkers present during the early post-mortem and known to be related to tenderness and pH decline and color development. pH values at 45 min, 3 h, and 30 h post-mortem were correlated with three, seven, and six biomarkers, respectively. L*a*b* color coordinates 24 h post-mortem were correlated with nine, five, and eight protein biomarkers, respectively. Regression models included Hsp proteins and explained between 47 and 59% of the variability between individuals in pH and between 47 and 65% of the variability in L*a*b* color coordinates. Proteins correlated with pH and/or color coordinates were involved in apoptosis or had antioxidative or chaperone activities. The main results include the negative correlations between pH45 min, pH3 h, and pHu and Prdx6, which may be explained by the antioxidative and phospholipase activities of this biomarker. Similarly, inducible Hsp70-1A/B and μ-calpain were correlated with L*a*b* coordinates, due to the protective action of Hsp70-1A/B on the proteolytic activities of μ-calpain on structural proteins. Correlations existed further between MDH1, ENO3, and LDH-B and pH decline and color stability probably due to the involvement of these enzymes in the glycolytic pathway and, thus, the energy status of the cell. The present results show that research using protein indicators may increase the understanding of early post-mortem biological mechanisms involved in pH and beef color development.

Sulfatide-Hsp70 interaction promotes Hsp70 clustering and stabilizes binding to unfolded protein

The 70-kDa heat shock protein (Hsp70), one of the major stress-inducible molecular chaperones, is localized not only in the cytosol, but also in extracellular milieu in mammals. Hsp70 interacts with various cell surface glycolipids including sulfatide (3'-sulfogalactosphingolipid). However, the molecular mechanism, as well as the biological relevance, underlying the glycolipid-Hsp70 interaction is unknown. Here we report that sulfatide promotes Hsp70 oligomerization through the N-terminal ATPase domain, which stabilizes the binding of Hsp70 to unfolded protein in vitro. We find that the Hsp70 oligomer has apparent molecular masses ranging from 440 kDa to greater than 669 kDa. The C-terminal peptide-binding domain is dispensable for the sulfatide-induced oligomer formation. The oligomer formation is impaired in the presence of ATP, while the Hsp70 oligomer, once formed, is unable to bind to ATP. These results suggest that sulfatide locks Hsp70 in a high-affinity state to unfolded proteins by clustering the peptide-binding domain and blocking the binding to ATP that induces the dissociation of Hsp70 from protein substrates.

The discovery of Hsp70 domain with cell-penetrating activity

Chaperone Hsp70 can cross the plasma membrane of living cells using mechanisms that so far have not received much research attention. Searching the part of the molecule that is responsible for transport ability of Hsp70, we found a cationic sequence composed of 20 amino acid residues on its surface, KST peptide, which was used in further experiments. We showed that KST peptide enters living cells of various origins with the same efficiency as the full-length chaperone. KST peptide is capable of carrying cargo with a molecular weight 30 times greater than its own into cells. When we compared the membrane-crossing activity of KST peptide in complex with Avidin (KST-Av complex) with that of similarly linked canonical TAT peptide, we found that TAT peptide penetrated SK-N-SH human neuroblastoma cells at a similar rate and efficiency as the KST peptide. Furthermore, KST peptide can carry protein complexes consisting of a specific antibody coupled to the peptide through the Avidin bridge. An antibody to Hsp70 delivered to SK-N-SH cells with high expression level of Hsp70 reduced the protective power of the chaperone and sensitized the cells to the pro-apoptotic effect of staurosporine. We studied the mechanisms of penetration of KST-Av and full-length Hsp70 inside human neuroblastoma SK-N-SH and human erythroleukemia K-562 cells and found that both used an active intracellular transport mechanism that included vesicular structures and negatively charged lipid membrane domains. Competition analysis of intracellular transport showed that the chaperone reduced intracellular penetration of KST peptide and conversely KST peptide prevented Hsp70 transport in a dose-dependent manner.

The effect of transportation of broilers during summer on the expression of heat shock protein 70, postmortem metabolism and meat quality

The objective of this study was to determine the effects of different transport times on broilers during summer on stress, meat quality, and early postmortem muscle metabolites. Arbor Acres broiler chickens (n = 105) were randomly categorized into 5 treatments: unstressed control, 0.5 h, 1 h, 2 h, and 4 h transport. Each treatment consisted of 3 replicates with 7 birds each. All birds (except the control group) were transported according to a designed protocol. With the extension of transport time, the activities of plasma creatine kinase (CK) and lactate dehydrogenase (LDH) gradually increased. The content of heat shock protein 70 (Hsp70) did not change significantly during 0.5 h transport compared to the control group, but was significantly higher (P < 0.05) at 1 h or more of transport time. Also, transport times of 2 h or more resulted in a death rate of 20%-33% of broilers. We found that the breast meat in the 0.5 h transport group had significantly (P < 0.05) higher L* values, drip loss, cooking loss, AMP/ATP ratio, and phosphorylation of AMP-activated protein kinase (p-AMPK). In addition, pH24h was lower compared to the control group, increasing the likelihood of pale, soft, and exudative (PSE)-like meat. However, no significant variations were found in meat color, drip loss, or cooking loss in other transport groups compared to the control group under the condition of this study. Muscle glycogen content decreased with time of transportation. There were significant correlations among p-AMPK and meat quality (P < 0.05). These results indicate that preslaughter transport during summer may cause severe physiological and biochemical changes of broilers. Further investigations studying the deeper relationship between biological indicators and meat quality according to the similar transport conditions would provide a better understanding of the effect of transport duration on meat quality.

Purification and characterisation of a phosphatidylcholine-binding protein from duck Biceps femoris muscle

The interaction between protein and phospholipids is a widespread phenomenon involving several physiological events in postmortem muscle. We hereby report a method for one-step purification of a phosphatidylcholine-binding (PC-binding) protein from duck Biceps femoris muscle with relatively high purity and yield using ion-exchange chromatography. This PC-binding protein has an inhibitory effect on the activity of phospholipase A2 (PLA2). A decrease (~62.3%) in PLA2 activity was observed. It had a strong affinity to bind PC at pH range of 6.2–6.8 with a peak at pH 6.6 (13.36 ± 0.48 g PC/g protein); in addition, raising ATP content from 1 to 5 μmol/mL enhanced the binding capacity. The PC-binding protein plays a potential role in the integrity of membrane and meat quality.

Sialyl-glycoconjugates in cholesterol-rich microdomains of P388 cells are the triggers for apoptosis induced by Rana catesbeiana oocyte ribonuclease

SBL/RC-RNase was originally isolated from frog (Rana catesbeiana) oocytes and purified as a novel sialic acid-binding lectin (SBL) that displayed strong anti-cancer activity. SBL was later shown to be identical to a ribonuclease (RC-RNase) from oocytes of the same species. The administration of SBL/RC-RNase induced apoptosis (with nuclear condensation and DNA fragmentation) in mouse leukemia P388 cells but did not kill umbilical vein endothelial or fibroblast cells derived from normal tissues. The cytotoxic activity of SBL/RC-RNase was inhibited by desialylation of P388 cells and/or the co-presence of free bovine submaxillary mucin. FACS analysis showed that SBL/RC-RNase was incorporated into cells after attachment to cholesterol-rich microdomains. Addition of the cholesterol remover methyl-β-cyclodextrin reduced SBL/RC-RNase-induced apoptosis. Apoptosis occurred through the caspase-3 pathway following activation of caspase-8 by SBL/RC-RNase. A heat shock cognate protein (Hsc70) and a heat shock protein (Hsp70) (each 70 kDa) on the cell membrane were shown to bind to SBL/RC-RNase by mass spectrometric and flow cytometric analyses. Quercetin, an inhibitor of Hsc70 and Hsp70, significantly reduced SBL/RC-RNase-induced apoptosis. Taken together, our findings suggest that sialyl-glycoconjugates present in cholesterol-rich microdomains form complexes with Hsc70 or Hsp70 that act as triggers for SBL/RC-RNase to induce apoptosis through a pathway involving the activation of caspase-3 and caspase-8.

HSP70 and lysosomal storage disorders: novel therapeutic opportunities

Lysosomes, with their arsenal of catabolic enzymes and crucial metabolic housekeeping functions are experiencing a revived research interest after having lived a rather quiet life for the last few decades. With the discovery of the interaction of the lysosomes with another ancient component of cellular homoeostasis, the molecular chaperone HSP70 (heat-shock protein 70), the stage seems set for further discoveries of the mechanisms regulating cellular and physiological stress responses to otherwise detrimental challenges.

Ca2+-induced effect on mechanical properties of sulfatide-incorporated vesicles

The Ca(2+)-induced effect on the nanomechanical properties of vesicles prepared at a different ratio of dipalmitoylphosphatidylcholine (DPPC)/sulfatide was studied using atomic force microscope (AFM) on a mica surface. Vesicles were prepared by extrusion and adsorbed on the mica surface. The forces, measured between an AFM tip and the vesicle, showed that the breakthrough of the tip into the vesicles occurred two times. Force data prior to the first breakthrough were fitted well with the Hertzian model to estimate Young's modulus and bending modulus of the vesicles. Sulfatide incorporation led to a decrease of around 90% in Young's modulus and bending modulus of the vesicles due to the hydration of the headgroups, while the addition of Ca(2+) induced dehydration to recover the properties. The change of the physical properties seems to be attributed to the headgroup packing order of the vesicles, which is determined by the interference with the hydration shell.

A subset of human pancreatic beta cells express functional CD14 receptors: a signaling pathway for beta cell-related glycolipids, sulfatide and β-galactosylceramide

BACKGROUND

T1DM is a T-cell-mediated autoimmune disease targeting insulin-producing beta-cells. Multiple factors may contribute to the development of T1DM. Among these, the metabolic state of beta-cells and pro-inflammatory cytokines, produced by infiltrating immune cells, have been implicated in the precipitation of T1DM.

METHODS AND RESULTS

In this study, confocal immunofluorescence microscopy of human pancreata revealed a distinct subset of beta-cells expressing the innate LPS co-receptor CD14. Human islets expressed fully functional CD14 as LPS stimulation led to a dose-dependent secretion of tumour necrosis factor (TNFα), interleukin (IL)-1β and IL-8, which were substantially inhibited by a blocking anti-CD14 mAb. In addition, LPS stimulation impaired the glucose-mediated insulin secretion in rat islets. β-GalCer and sulfatide, glycolipids that are related to insulin processing and secretion, are possibly interacting with the CD14 receptor complex. β-GalCer had an LPS-like, serum- and CD14-dependent effect on the induction of pro-inflammatory cytokines in a human monocyte cell line. In contrast, the LPS-mediated cytokine production was inhibited by sulfatide. Human islets also responded to β-GalCer (10 µg/mL) by secreting TNFα, IL-1β and IL-8, whereas sulfatide partly inhibited the effect of LPS.

CONCLUSIONS

A subset of human beta-cells expresses functional CD14 receptor and thus is able to recognize both exogenous bacterial (LPS) as well as endogenous ligands (e.g. glycolipids of beta-cell origin). The CD14 expression on a subset of human beta-cells may play a role in the innate surveillance of the endocrine environment but may also contribute to innate immune mechanisms in the early stages of beta-cell aggression.

C-Mannosylated peptides derived from the thrombospondin type 1 repeat interact with Hsc70 to modulate its signaling in RAW264.7 cells

The thrombospondin type 1 repeat (TSR) is a functional module of proteins called TSR superfamily proteins (e.g., thrombospondin, F-spondin, mindin, etc.) and includes a conserved Trp-x-x-Trp (W-x-x-W) motif, in which the first Trp residue is preferably modified by C-mannosylation. We previously reported that synthesized C-mannosylated TSR-derived peptides (e.g., C-Man-WSPW) specifically enhanced lipopolysaccharide-induced signaling in macrophage-like RAW264.7 cells. In this study, we searched for the proteins that bind to C-mannosylated TSR-derived peptides in RAW264.7 cells and identified heat shock cognate protein 70 (Hsc70). The binding affinity of Hsc70 for C-mannosylated peptides in solution was higher than that for the peptides without C-mannose. The binding was influenced by a nucleotide-induced conformational change of Hsc70, and C-mannosylated peptides preferred the substrate-binding domain of Hsc70. Furthermore, in RAW264.7 cells, addition of Hsc70 stimulated cellular signaling to produce tumor necrosis factor-alpha, via transforming growth factor-beta-activated kinase 1, and the Hsc70-induced signaling was enhanced more in the presence of the peptides with C-mannose than that without C-mannose, suggesting functional interaction between Hsc70 and the C-mannosylated peptides in the cells. Together, these results demonstrate a novel function of the C-mannosylation of TSR-derived peptides in terms of interaction with Hsc70 to regulate cellular signaling.

Glycosphingolipids in microdomain formation and their spatial organization

Plasma membranes regulate the influx and efflux of molecules across themselves and are also responsible for primary signal transduction between cells or within the same cell. Presence of lateral heterogeneity and the ability of reorganization are essential requirements for effective functioning of biomembranes. Lipid rafts are small, heterogeneous, dynamic domains enriched in glycosphingolipids, sphingomyelin and cholesterol, and profoundly influence membrane organization. Glycosphingolipids are inclined towards formation of liquid-ordered phases in membranes, both with and without cholesterol; they are therefore prime players in domain formation. Here, we discuss the role of glycosphingolipids in microdomain formation and their spatial organization within these rafts.

Glycobiology in the cytosol: the bitter side of a sweet world

Progress in glycobiology has undergone explosive growth over the past decade with more of the researchers now realizing the importance of glycan chains in various inter- and intracellular processes. However, there is still an area of glycobiology awaiting exploration. This is especially the case for the field of "glycobiology in the cytosol" which remains rather poorly understood. Yet evidence is accumulating to demonstrate that the glycoconjugates and their recognition molecules (i.e. lectins) are often present in this subcellular compartment.

Membranes: a meeting point for lipids, proteins and therapies

Membranes constitute a meeting point for lipids and proteins. Not only do they define the entity of cells and cytosolic organelles but they also display a wide variety of important functions previously ascribed to the activity of proteins alone. Indeed, lipids have commonly been considered a mere support for the transient or permanent association of membrane proteins, while acting as a selective cell/organelle barrier. However, mounting evidence demonstrates that lipids themselves regulate the location and activity of many membrane proteins, as well as defining membrane microdomains that serve as spatio-temporal platforms for interacting signalling proteins. Membrane lipids are crucial in the fission and fusion of lipid bilayers and they also act as sensors to control environmental or physiological conditions. Lipids and lipid structures participate directly as messengers or regulators of signal transduction. Moreover, their alteration has been associated with the development of numerous diseases. Proteins can interact with membranes through lipid co-/post-translational modifications, and electrostatic and hydrophobic interactions, van der Waals forces and hydrogen bonding are all involved in the associations among membrane proteins and lipids. The present study reviews these interactions from the molecular and biomedical point of view, and the effects of their modulation on the physiological activity of cells, the aetiology of human diseases and the design of clinical drugs. In fact, the influence of lipids on protein function is reflected in the possibility to use these molecular species as targets for therapies against cancer, obesity, neurodegenerative disorders, cardiovascular pathologies and other diseases, using a new approach called membrane-lipid therapy.

High-throughput screen for small molecules that modulate the ATPase activity of the molecular chaperone DnaK

DnaK is a molecular chaperone of Escherichia coli that belongs to a family of conserved 70-kDa heat shock proteins. The Hsp70 chaperones are well known for their crucial roles in regulating protein homeostasis, preventing protein aggregation, and directing subcellular traffic. Given the complexity of functions, a chemical method for controlling the activities of these chaperones might provide a useful experimental tool. However, there are only a handful of Hsp70-binding molecules known. To build this area, we developed a robust, colorimetric, high-throughput screening (HTS) method in 96-well plates that reports on the ATPase activity of DnaK. Using this approach, we screened a 204-member focused library of molecules that share a dihydropyrimidine core common to known Hsp70-binding leads and uncovered seven new inhibitors. Intriguingly, the candidates do not appear to bind the hydrophobic groove that normally interacts with peptide substrates. In sum, we have developed a reliable HTS method that will likely accelerate discovery of small molecules that modulate DnaK/Hsp70 function. Moreover, because this family of chaperones has been linked to numerous diseases, this platform might be used to generate new therapeutic leads.