Designing de Novo Small Molecules That Control Heat Shock Protein 70 (Hsp70) and Heat Shock Organizing Protein (HOP) within the Chaperone Protein-Folding Machinery

Rationally modified SNX-class Hsp90 inhibitors disrupt extracellular fibronectin assembly without intracellular Hsp90 activity

Despite Hsp90's well documented promise as a target for developing cancer chemotherapeutics, its inhibitors have struggled to progress through clinical trials. This is, in part, attributed to the cytoprotective compensatory heat shock response (HSR) stimulated through intracellular Hsp90 inhibition. Beyond its intracellular role, secreted extracellular Hsp90 (eHsp90) interacts with numerous pro-oncogenic extracellular clients. This includes fibronectin, which in the tumour microenvironment enhances cell invasiveness and metastasis. Through the rational modification of known Hsp90 inhibitors (SNX2112 and SNX25a) we developed four Hsp90 inhibitory compounds, whose alterations restricted their interaction with intracellular Hsp90 and did not stimulate the HSR. Two of the modified cohort (compounds 10 and 11) were able to disrupt the assembly of the extracellular fibronectin network at non-cytotoxic concentrations, and thus represent promising new tool compounds for studying the druggability of eHsp90 as a target for inhibition of tumour invasiveness and metastasis.

Hsp70/Hsp90 Organising Protein (Hop): Coordinating Much More than Chaperones

The Hsp70/Hsp90 organising protein (Hop, also known as stress-inducible protein 1/STI1/STIP1) has received considerable attention for diverse cellular functions in both healthy and diseased states. There is extensive evidence that intracellular Hop is a co-chaperone of the major chaperones Hsp70 and Hsp90, playing an important role in the productive folding of Hsp90 client proteins, although recent evidence suggests that eukaryotic Hop is regulatory within chaperone complexes rather than essential. Consequently, Hop is implicated in many key signalling pathways, including aberrant pathways leading to cancer. Hop is also secreted, and it is now well established that Hop interacts with the prion protein, PrP^C, to mediate multiple signalling events. The intracellular and extracellular forms of Hop most likely represent two different isoforms, although the molecular determinants of these divergent functions are yet to be identified. There is also a growing body of research that reports the involvement of Hop in cellular activities that appear independent of either chaperones or PrP^C. While the various cellular functions of Hop have been described, its biological function remains elusive. However, recent knockout studies in mammals suggest that Hop has an important role in embryonic development. This review provides a critical overview of the latest molecular, cellular and biological research on Hop, critically evaluating its function in healthy systems and how this function is adapted in diseased states.

A campaign targeting a conserved Hsp70 binding site uncovers how subcellular localization is linked to distinct biological activities

The potential of small molecules to localize within subcellular compartments is rarely explored. To probe this question, we measured the localization of Hsp70 inhibitors using fluorescence microscopy. We found that even closely related analogs had dramatically different distributions, with some residing predominantly in the mitochondria and others in the ER. CRISPRi screens supported this idea, showing that different compounds had distinct chemogenetic interactions with Hsp70s of the ER (HSPA5/BiP) and mitochondria (HSPA9/mortalin) and their co-chaperones. Moreover, localization seemed to determine function, even for molecules with conserved binding sites. Compounds with distinct partitioning have distinct anti-proliferative activity in breast cancer cells compared with anti-viral activity in cellular models of Dengue virus replication, likely because different sets of Hsp70s are required in these processes. These findings highlight the contributions of subcellular partitioning and chemogenetic interactions to small molecule activity, features that are rarely explored during medicinal chemistry campaigns.

Multivalent protein-protein interactions are pivotal regulators of eukaryotic Hsp70 complexes

Heat shock protein 70 (Hsp70) is a molecular chaperone and central regulator of protein homeostasis (proteostasis). Paramount to this role is Hsp70's binding to client proteins and co-chaperones to produce distinct complexes, such that understanding the protein-protein interactions (PPIs) of Hsp70 is foundational to describing its function and dysfunction in disease. Mounting evidence suggests that these PPIs include both "canonical" interactions, which are universally conserved, and "non-canonical" (or "secondary") contacts that seem to have emerged in eukaryotes. These two categories of interactions involve discrete binding surfaces, such that some clients and co-chaperones engage Hsp70 with at least two points of contact. While the contributions of canonical interactions to chaperone function are becoming increasingly clear, it can be challenging to deconvolute the roles of secondary interactions. Here, we review what is known about non-canonical contacts and highlight examples where their contributions have been parsed, giving rise to a model in which Hsp70's secondary contacts are not simply sites of additional avidity but are necessary and sufficient to impart unique functions. From this perspective, we propose that further exploration of non-canonical contacts will generate important insights into the evolution of Hsp70 systems and inspire new approaches for developing small molecules that tune Hsp70-mediated proteostasis.

De Novo Design, Synthesis, and Mechanistic Evaluation of Short Peptides That Mimic Heat Shock Protein 27 Activity

We report the first small molecule peptides based on the N-terminal sequence of heat shock protein 27 (Hsp27, gene HSPB1) that demonstrates chaperone-like activity. The peptide, comprising the SWDPF sequence located at Hsp27's amino (N)-terminal domain, directly regulates protein aggregation events, maintaining the disaggregated state of the model protein, citrate synthase. While traditional inhibitors of protein aggregation act via regulation of a protein that facilitates aggregation or disaggregation, our molecules are the first small peptides between 5 and 8 amino acids in length that are based on the N-terminus of Hsp27 and directly control protein aggregation. The presented strategy showcases a new approach for developing small peptides that control protein aggregation in proteins with high aggregate levels, making them a useful approach in developing new drugs.

Significance of changes of serum heat shock protein 70 levels in patients with traumatic brain injury and acute gastrointestinal injury

BACKGROUND

At present, most researchers believe that serum heat shock protein 70 (HSP70) has a high sensitivity when gastrointestinal function is damaged and it is a sensitive indicator of early intestinal ischemia. However, there are few studies on the role of serum HSP70 in the evaluation of gastrointestinal function in patients with traumatic brain injury (TBI), which is worthy of further study.

AIM

To explore the significance of changes of serum heat shock protein 70 (HSP70) levels in patients with TBI combined with acute gastrointestinal injury (AGI).

METHODS

A total of 133 patients with TBI and AGI who were treated and hospitalized at the intensive care unit of Tianjin Medical University General Hospital from March 2019 to October 2020 were selected as the research subjects. According to the modified Glasgow coma scoring method combined with the clinical classification criteria of traumatic brain injury, the study subjects were divided into three groups: 63 cases of mild type, 32 cases of moderate type, and 38 cases of severe type. According to the AGI grading standard, the study subjects were divided into 68 cases of grade I AGI, 37 cases of grade II, 17 cases of grade III, and 11 cases of grade IV. Another 50 patients with no history of TBI and basic diseases of various systems who underwent routine physical examination at our hospital were selected as a control group. Serum HSP70 levels were compared between patients with different brain trauma types and different AGI grades and the control group. The correlation of serum HSP70 levels of TBI patients with AGI and the degree with brain injury and AGI grades was analyzed. The performance of serum HSP70 levels in the diagnosis of TBI with AGI was evaluated.

RESULTS

On the day of admission, as the degree of brain injury worsened, serum HSP70 level gradually increased, and HSP70 levels of various types were significantly higher than those in the control group. As the AGI grade increased, serum HSP70 level also gradually increased. And the HSP70 levels of each grade were significantly higher than those in the control group (P < 0.05). On the 3rd day of admission, serum HSP70 levels of each type were significantly lower than the values on the day of admission, but the values were still higher than those in the control group. And serum HSP70 level of each grade was significantly lower than the value on the day of admission, but the value was still significantly higher than that of the control group (P < 0.05). Pearson correlation analysis indicated that serum HSP70 levels were significantly positively correlated with the degree of brain injury and AGI grades in patients with TBI and AGI (r_s = 0.802 and 0.836, respectively, P < 0.01). ROC curve analysis showed that the accuracy of serum HSP70 in the diagnosis of TBI combined with AGI was relatively high, with an AUC of 0.803 and 95%CI of 0.720-0.872. When the best cutoff value was 258.50 ng/L, the sensitivity was 80.94%, the specificity was 87.93%, and the Youden index was 0.501.

CONCLUSION

Serum HSP70 in patients with TBI combined with AGI is significantly up-regulated, which may be related to the progression of the disease and has high diagnostic value for TBI combined with AGI.

Modulation of protein fate decision by small molecules: targeting molecular chaperone machinery

Modulation of protein fate decision and protein homeostasis plays a significant role in altering the protein level, which acts as an orientation to develop drugs with new mechanisms. The molecular chaperones exert significant biological functions on modulation of protein fate decision and protein homeostasis under constantly changing environmental conditions through extensive protein–protein interactions (PPIs) with their client proteins. With the help of molecular chaperone machinery, the processes of protein folding, trafficking, quality control and degradation of client proteins could be arranged properly. The core members of molecular chaperones, including heat shock proteins (HSPs) family and their co-chaperones, are emerging as potential drug targets since they are involved in numerous disease conditions. Development of small molecule modulators targeting not only chaperones themselves but also the PPIs among chaperones, co-chaperones and clients is attracting more and more attention. These modulators are widely used as chemical tools to study chaperone networks as well as potential drug candidates for a broader set of diseases. Here, we reviewed the key checkpoints of molecular chaperone machinery HSPs as well as their co-chaperones to discuss the small molecules targeting on them for modulation of protein fate decision.

Allosteric Regulation at the Crossroads of New Technologies: Multiscale Modeling, Networks, and Machine Learning

Allosteric regulation is a common mechanism employed by complex biomolecular systems for regulation of activity and adaptability in the cellular environment, serving as an effective molecular tool for cellular communication. As an intrinsic but elusive property, allostery is a ubiquitous phenomenon where binding or disturbing of a distal site in a protein can functionally control its activity and is considered as the "second secret of life." The fundamental biological importance and complexity of these processes require a multi-faceted platform of synergistically integrated approaches for prediction and characterization of allosteric functional states, atomistic reconstruction of allosteric regulatory mechanisms and discovery of allosteric modulators. The unifying theme and overarching goal of allosteric regulation studies in recent years have been integration between emerging experiment and computational approaches and technologies to advance quantitative characterization of allosteric mechanisms in proteins. Despite significant advances, the quantitative characterization and reliable prediction of functional allosteric states, interactions, and mechanisms continue to present highly challenging problems in the field. In this review, we discuss simulation-based multiscale approaches, experiment-informed Markovian models, and network modeling of allostery and information-theoretical approaches that can describe the thermodynamics and hierarchy allosteric states and the molecular basis of allosteric mechanisms. The wealth of structural and functional information along with diversity and complexity of allosteric mechanisms in therapeutically important protein families have provided a well-suited platform for development of data-driven research strategies. Data-centric integration of chemistry, biology and computer science using artificial intelligence technologies has gained a significant momentum and at the forefront of many cross-disciplinary efforts. We discuss new developments in the machine learning field and the emergence of deep learning and deep reinforcement learning applications in modeling of molecular mechanisms and allosteric proteins. The experiment-guided integrated approaches empowered by recent advances in multiscale modeling, network science, and machine learning can lead to more reliable prediction of allosteric regulatory mechanisms and discovery of allosteric modulators for therapeutically important protein targets.

KLR-70: A Novel Cationic Inhibitor of the Bacterial Hsp70 Chaperone

The heat-shock factor Hsp70 and other molecular chaperones play a central role in nascent protein folding. Elucidating the task performed by individual chaperones within the complex cellular milieu, however, has been challenging. One strategy for addressing this goal has been to monitor protein biogenesis in the absence and presence of inhibitors of a specific chaperone, followed by analysis of folding outcomes under both conditions. In this way, the role of the chaperone of interest can be discerned. However, development of chaperone inhibitors, including well-known proline-rich antimicrobial peptides, has been fraught with undesirable side effects, including decreased protein expression yields. Here, we introduce KLR-70, a rationally designed cationic inhibitor of the Escherichia coli Hsp70 chaperone (also known as DnaK). KLR-70 is a 14-amino acid peptide bearing naturally occurring residues and engineered to interact with the DnaK substrate-binding domain. The interaction of KLR-70 with DnaK is enantioselective and is characterized by high affinity in a buffered solution. Importantly, KLR-70 does not significantly interact with the DnaJ and GroEL/ES chaperones, and it does not alter nascent protein biosynthesis yields across a wide concentration range. Some attenuation of the anti-DnaK activity of KLR-70, however, has been observed in the complex E. coli cell-free environment. Interestingly, the d enantiomer D-KLR-70, unlike its all-L KLR-70 counterpart, does not bind the DnaK and DnaJ chaperones, yet it strongly inhibits translation. This outcome suggests that the two enantiomers (KLR-70 and D-KLR-70) may serve as orthogonal inhibitors of chaperone binding and translation. In summary, KLR-70 is a novel chaperone inhibitor with high affinity and selectivity for bacterial Hsp70 and with considerable potential to help in parsing out the role of Hsp70 in nascent protein folding.

Hsp70 and the Unfolded Protein Response as a Challenging Drug Target and an Inspiration for Probe Molecule Development

The unfolded protein response (UPR) is a cellular stress response mechanism that is critical for cell survival. Pharmacological modulation of the ATPase activity of the chaperone Hsp70 can trigger UPR-mediated cell death, thus removing pathogenic cells in human malignancies, or, alternatively, stimulate survival, thereby preventing apoptosis in neuronal cells and slowing the progress of inflammation, neurodegeneration, and aging. This Viewpoint highlights the complexity of the protein homeostasis network and discusses different approaches for modulating Hsp70 activity, including the use of a chemical reaction development-inspired library of Hsp70 agonists and antagonists.

Modulating protein-protein interaction networks in protein homeostasis

Protein-protein interactions (PPIs) occur in complex networks. These networks are highly dependent on cellular context and can be extensively altered in disease states such as cancer and viral infection. In recent years, there has been significant progress in developing inhibitors that target individual PPIs either orthosterically (at the interface) or allosterically. These molecules can now be used as tools to dissect PPI networks. Here, we review recent examples that highlight the use of small molecules and engineered proteins to probe PPIs within the complex networks that regulate protein homeostasis. Researchers have discovered multiple mechanisms to modulate PPIs involved in host/viral interactions, deubiquitinases, the ATPase p97/VCP, and HSP70 chaperones. However, few studies have evaluated the effect of such modulators on the target's network or have compared the biological implications of different modulation strategies. Such studies will have an important impact on next generation therapeutics.