Heat, pH induced aggregation and surface hydrophobicity of S. cerevesiae Ssa1 protein

Designing Specific HSP70 Substrate Binding Domain Inhibitor for Perturbing Protein Folding Pathways to Inhibit Cancer Mechanism

BACKGROUND

HSP70 is a survival factor for tumor cells in transformation and in tumor progression as well as in anti-apoptotic response.

OBJECTIVE

Several inhibitors targeting HSP70 ATPase function displayed off-target effects, but PES, which targets the HSP70 substrate binding domain, prevents tumor cell survival prominently. However, PES may not bind HSP70 in the absence of nucleotide. This research aimed to design a unique inhibitor molecule that works both in the presence and absence of nucleotides to amplify inhibition.

METHODS

A set of chimeric coumarine-pyrazole derivatives were determined by in silico techniques and synthesized to elucidate their inhibitory effects. Cell viability experiments displayed KBR1307 as the most efficient inhibitor. A set of characterization experiments were performed, and the results were compared to that of PES agent. Binding constant, ATP hydrolysis rate, and percent aggregation were determined in the presence and absence of inhibitors.

RESULTS

In silico docking experiments showed that only KBR1307 binds the HSP70 substrate binding domain and interacts with cochaperone interface. Binding experiments indicated that KBR1307 binds HSP70 both in the presence and absence of nucleotides, but PES does not. Both inhibitors significantly lower HSP70 ATPase activity and substrate protein disaggregation activity. However, KBR1307 displays a lower IC₅₀ value at the MCF-7 cell line compared to PES. Both inhibitors do not alter HSP70 secondary structure composition and overall stability.

CONCLUSION

KBR1307 effectively inhibits HSP70 compared to PES and provides a promising template for novel anticancer drug development.

The Role of Surface Properties on Protein Aggregation Behavior in Aqueous Solution of Different pH Values

This study aimed to investigate the effect of pH-mediated surface properties of bovine serum albumin (BSA) on protein aggregation and the changes of protein structure and colloidal stability at different solution pH levels. The hydrophobicity of BSA surface was characterized by endogenous fluorescence spectroscopy, fluorescence quenching of acrylamide, and fluorescence probe. The results showed that the hydrophobicity of BSA surface was similar at pH 5, 6, 7.4, followed by pH 4, 8, 9, 10, and finally by pH 3 and 11 with strong acidity and alkalinity. The positive charge on the BSA surface was increased gradually with the decrease of solution pH, while the negative charge on protein surface was increased gradually with the increase of solution pH. The degree of protein aggregation was examined by turbidimetry, flow cytometry, and SDS-PAGE. The results showed that the oscillating aggregation of BSA did not change with the solution pH, but was partially dependent on the relative contribution of electrostatic and hydrophobic interactions between the protein molecules. In addition, the secondary structure, conformational stability, unfolding degree, and colloidal stability of proteins were investigated by circular dichroism, fluorescence spectroscopy, protein pulse hydrolysis, and dynamic light scattering, respectively. The results suggested that the solution pH could change the structure and stability of the protein at different levels. Solution pH has distinct effects on the structural stability of protein at different levels. The change of protein surface properties mediated by solution pH is related to protein aggregation.

A highly efficient, one-step purification of the Hsp70 chaperone Ssa1

Chaperone proteins are required to maintain the overall fold and function of proteins in the cell. As part of the Hsp70 family, Ssa1 acts to maintain cellular proteostasis through a variety of diverse pathways aimed to preserve the native conformation of target proteins, thereby preventing aggregation and future states of cellular toxicity. Studying the structural dynamics of Ssa1 in vitro is essential to determining their precise mechanisms and requires the development of purification methods that result in highly pure chaperones. Current methods of expressing and purifying Ssa1 utilize affinity tagged constructs expressed in Escherichia coli, however, expression in an exogenous source produces proteins that lack post-translational modifications leading to undesired structural and functional effects. Current protocols to purify Ssa1 from Saccharomyces cerevisiae require large amounts of starting material, multiple steps of chromatography, and result in low yield. Our objective was to establish a small-scale purification of Ssa1 expressed from its endogenous source, Saccharomyces cerevisiae, with significant yield and purity. We utilized a protein A affinity tag that was previously used to purify large protein complexes from yeast, combined with magnetic Dynabeads that are conjugated with rabbit immunoglobulin G (IgG). Our results show that we can produce native, highly pure, active Ssa1 via this one-step purification with minimal amounts of starting material, and this Ssa1-protein A fusion does not alter cellular phenotypes. This methodology is a significant improvement in Ssa1 purification and will facilitate future experiments that will elucidate the biochemical and biophysical properties of Hsp70 chaperones.

The Hsp60 protein of helicobacter pylori displays chaperone activity under acidic conditions

The heat shock protein, Hsp60, is one of the most abundant proteins in Helicobacter pylori. Given its sequence homology to the Escherichia coli Hsp60 or GroEL, Hsp60 from H. pylori would be expected to function as a molecular chaperone in this organism. H. pylori is an organism that grows on the gastric epithelium, where the pH can fluctuate between neutral and 4.5 and the intracellular pH can be as low as 5.0. This study was performed to test the ability of Hsp60 from H. pylori to function as a molecular chaperone under mildly acidic conditions. We report here that Hsp60 could suppress the acid-induced aggregation of alcohol dehydrogenase (ADH) in the 7.0-5.0 pH range. Hsp60 was found to undergo a conformational change within this pH range. It was also found that exposure of hydrophobic surfaces of Hsp60 is significant and that their exposure is increased under acidic conditions. Although, alcohol dehydrogenase does not contain exposed hydrophobic surfaces, we found that their exposure is triggered at low pH. Our results demonstrate that Hsp60 from H. pylori can function as a molecular chaperone under acidic conditions and that the interaction between Hsp60 and other proteins may be mediated by hydrophobic interactions.

Isolation and characterization of Heat Shock Protein 100-Batu1 from Toxoplasma gondii RH strain

Toxoplasma gondii is an intracellular parasitic protozoon which infects human and most warm-blooded animals. Almost one-third of the world's population is affected by life-threatening infection of T. gondii tachyzoites form. Slow growing, transmissible and encysted bradyzoites forms are composed after tachyzoites stage. Cellular and environmental stresses induce conversion of tachyzoites from bradyzoites and this condition is associated with Heat Shock Protein (Hsps) family. Hsp100 is a member of this protein family, and coordinates to disassemble protein aggregates with Hsp70 and Hsp40 in an ATP dependent manner. Several proteins are involved during this stage differentiation and Hsp100 may help them to be in their native soluble form to perform their function as observed in other organisms. For this purpose, Hsp100-Batu1 was isolated from T. gondii RH strain to characterize its biochemical properties in this current study. Hsp100 proteins play a role in survival and virulence of pathogens as shown in the literature. Therefore, manipulation of protein-protein interaction may perturb T. gondii infection and impair conversion to tachyzoites by inhibiting Hsp100 function. Therefore, results of this work present a potential route for vaccination or immunotherapy.

Fungal invasion of epithelial cells

Interaction between host cells and invasive Candida plays a large role in the pathogenicity of Candida species. Fungal-induced endocytosis and active penetration are the two distinct, yet complementary invasion mechanisms of invasive candidiasis. Induced endocytosis is a microorganism-triggered, epithelial-driven, clathrin-mediated and actin-dependent process. During the fundamental pathological process of induced endocytosis, invasins (Als3 and Ssa1), which mediate the binding of host epithelial surface proteins, are expressed by Candida species on the hyphal surface. Sequentially, the interaction between invasins and host epithelial surface proteins stimulates the recruitment of clathrin, dynamin and cortactin to the sites where Candida enters epithelial cells, which in turn induce the actin cytoskeleton reorganization. Actin cytoskeleton provides the force required for fungal internalization. Parallely, active penetration of Candida can directly pass through epithelial cells possibly due to progressive elongation of hyphae and physical forces. Several molecules, such as secreted hydrolases and Als3, can affect the protective barrier of the epithelium and make Candida actively penetrate into epithelial cells through intercellular gaps of epithelial layers.