Discipline: Chemistry and Chemical Sciences
Subcategory: Biochemistry (not Cell and Molecular Biology and Genetics)
Brittini Roye - University of the District of Columbia
Co-Author(s): Dana Rhea, University of the District of Columbia
The cysteine proteases are a large group of enzymes that play roles in a broad range of biological processes. Disturbance of the natural equilibrium of enzymatic activity of the cysteine proteases, responsible for protein degradation, may lead to a variety of pathological conditions, including Alzheimer’s, stroke and cancer. Inhibitors can restore the natural balance through regulation of these enzymes and therefore present an opportunity for drug development. The primary objective of this project is to investigate whether triorganotin can inhibit the enzymatic activity of thiol-dependent cysteine proteases. The research is based on the hypothesis that a triorganotin complex has a strong interaction with the thiol group and can inhibit a cysteine protease by ligand exchange with the thiol of the active site cysteine. In this experiment, commercially available tributyltin acetate chosen as the tin inhibitor against Papain, a cysteine protease used in this project. The enzymatic activities of both pure and inhibited papain solutions were recorded based on the amount of tyrosine released in digesting reaction of Casein. The Folin’s reagent was used to react with free tyrosine to produce a blue colored chromophore, which was quantifiable and measured as an absorbance under 660 nm on the spectrophotometer. A standard curve has been generated by reacting known quantities of tyrosine with the Folin’s reagent to correlate the enzymatic activity and the absorbance. Preliminary data has shown the inhibition of enzymatic activity of Papain by tributyltin acetate. The absorbance of the chromophore was observed to decrease from 0.215, when no tributyltin acetate was mixed with papain, to 0.113 when 0.2 to 2 ppm of tributyltin acetate was added to papain in acetone. However, the inhibition of tributyltin acetate showed no significant difference when the tin concentration was changed in acetone. This could be due to the failure in reactivating the thiol sites in papain when thiol containing reactivating agent preferably coordinated to tin complex . Preliminary data also showed dimethyl sulfoxide (DMSO) when used as the solvent, no inhibition was observed for tributyltin acetate. This indicated that tin has a very strong affinity towards DMSO and the coordination of DMSO to tin makes no available site for the nucleophilic attack from the thiol group. Future studies of this project will focus on collecting the evidence of interaction between tin and thiol group of the cysteine protease through NMR studies.
Funder Acknowledgement(s): Funding was provided by the NSF/HRD1531014 and 1622811 grants.
Faculty Advisor: Dr. Xueqing Song, firstname.lastname@example.org
Role: I conducted the enzymatic activity assay with colorimetric detection and the spectrophotometric analysis .