Human prostate-specific antigen: structural and functional similarity with serine proteases

Area of Science:

• Biochemistry
• Proteomics
• Enzymology

Background:

• Prostate-specific antigen (PSA) is a serine protease found in seminal plasma.
• Understanding PSA's primary structure and enzymatic properties is crucial for its role in diagnostics and therapeutics.

Purpose of the Study:

• To determine the complete amino acid sequence of human prostate-specific antigen (PSA).
• To characterize the enzymatic activity and substrate specificity of PSA.
• To investigate the inhibition of PSA activity.

Main Methods:

• Peptide generation using cyanogen bromide, hydroxylamine, endoproteinases Arg-C, and Lys-C.
• Amino acid sequencing of generated peptides.
• Enzymatic activity assays using chromogenic substrates and protein substrates.
• Analysis of inhibition by protease inhibitors and metal ions.

Main Results:

• The complete amino acid sequence of PSA (240 residues) was determined, showing homology to kallikrein family serine proteases.
• PSA possesses both chymotrypsin-like and trypsin-like enzymatic activities, with specific cleavage sites identified on various proteins.
• Enzymatic activity of PSA was effectively inhibited by PMSF, DFP, aprotinin, leupeptin, soybean trypsin inhibitor, Zn2+, and spermidine.

Conclusions:

• The primary structure of PSA is elucidated, confirming its classification within the serine protease family.
• PSA demonstrates broad substrate specificity, cleaving peptide bonds after hydrophobic and basic residues.
• The identified inhibitors provide insights into PSA's catalytic mechanism and potential therapeutic strategies.