Proteolytic enzymes as structural probes for ribonuclease BS-1

Area of Science:

• Biochemistry
• Enzymology
• Protein Structure

Background:

• Bovine seminal ribonuclease (BS-1) is a dimeric protein with subunits homologous to bovine pancreatic ribonuclease A.
• Understanding the conformational properties of BS-1 is crucial for elucidating its structure-function relationship.

Purpose of the Study:

• To investigate the conformational structure of bovine seminal ribonuclease BS-1 using proteolytic enzymes as probes.
• To compare the structural features of BS-1 with bovine pancreatic ribonuclease A.

Main Methods:

• Treatment of BS-1, ribonuclease A, and a monomeric BS-1 derivative with trypsin, pepsin, and subtilisin.
• Analysis of the effects of these enzymes on the proteins under specific conditions.

Main Results:

• Pepsin demonstrated high similarity between the C-terminal regions of pancreatic and seminal ribonucleases.
• Subtilisin resistance in BS-1's N-terminal region is due to its conformation, involving proline at position 19, not its dimeric state.
• Monomeric BS-1 is susceptible to trypsin only when dissociated, suggesting conformational changes or exposure of interfaces.

Conclusions:

• The C-termini of pancreatic and seminal ribonucleases share significant structural similarity.
• The conformation of the N-terminal region, influenced by proline 19, dictates subtilisin resistance in BS-1.
• Dissociation of BS-1 exposes previously hidden sites to tryptic digestion, highlighting the role of quaternary structure in enzyme resistance.