Date of Completion

7-2021

Document Type

Thesis

Degree Name

Bachelor of Science in Biochemistry

Keywords

Amino Acids, Papain, Cystatins

Abstract

Papain is a cysteine protease enzyme found in papaya known for its proteolytic activity. Its activity is dependent on its (1) key active sites: Cys-25, His-159, and Asp-175; (2) inhibitor; and (3) substrate. In this study, the active sites of Papain were modified in silico to propose en]\me modifications that would likel\ increase the en]\me¶s proteol\tic activit\ b\ reducing binding with the inhibitor (Cystatin D) and maintaining or increasing binding with proteolysis targets (Bovine serum albumin). UCSF Chimera was used to modify the structure of Papain and to determine if each modified Papain enzyme had interactions with the inhibitor and substrate that were favorable for increased proteolytic activity. Comparison of bond distances between the original and modified enzyme and substrate binding showed that for single replacements, replacing histidine at position 25 gave the most favorable modification for increased proteolytic activity as it reduces the interaction with the Cystatin D inhibitor while maintaining a similar binding to BSA. Similarly, C25H/H159K was identified as the most favorable modification for double replacement for increased proteolytic activity. It has been concluded that these modified Papain enzymes have optimized binding for proteolytic activity due to the reduced interaction with inhibitor Cystatin D when ingested orally for medicines and treatment. However, as the experiment is conducted in-silico, further testing would need to be conducted to determine the efficacy and efficiency of binding for medicinal use. Also, as BSA was used as the general proteolysis target, further additional testing may need to be conducted to determine if the modified enzymes function similarly to the original Papain target with other proteolysis targets to maintain its medicinal purpose.

First Advisor

Tabitha L. Amora

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