Zinc-alpha 2-glycoprotein has ribonuclease activity

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Zinc-alpha 2-glycoprotein (Zn alpha 2gp) is a protein found in body fluids and epithelia.
• Its precise biological function has remained largely unknown despite gene sequencing.

Purpose of the Study:

• To investigate the functional properties of Zinc-alpha 2-glycoprotein (Zn alpha 2gp).
• To characterize the enzymatic activity of Zn alpha 2gp, specifically its potential as a ribonuclease.

Main Methods:

• Enzyme activity assays were performed using synthetic polyribonucleotide substrates.
• RNase activity was characterized across varying pH, ionic strength, and temperature conditions.
• Inhibition studies were conducted using ZnCl2, MgCl2, and a placental RNase inhibitor.

Main Results:

• Zn alpha 2gp was found to possess RNase activity, comparable to onconase but significantly less than RNase A.
• Optimal activity was observed at pH 7.5, 50 mM NaCl, and 60°C.
• The enzyme's activity is specific for pyrimidine residues on single-stranded RNA and is inhibited by ZnCl2 and placental RNase inhibitor.
• Zn alpha 2gp shares an N-terminal pyroglutamic acid residue with onconase, a feature linked to RNase activity.

Conclusions:

• Zinc-alpha 2-glycoprotein (Zn alpha 2gp) possesses intrinsic RNase activity, a novel finding that expands its known biological roles.
• The characterized enzymatic properties provide a basis for understanding Zn alpha 2gp's function in cellular processes.
• Despite structural similarities to MHC proteins, Zn alpha 2gp's identified RNase function suggests roles beyond immune response.