The ribonucleolytic activity of angiogenin

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Angiogenin (ANG) is a protein homologue to ribonuclease A (RNase A) involved in angiogenesis.
• ANG's biological activity is intrinsically linked to its ribonucleolytic function, albeit at a lower level than RNase A.
• Efficient production of functional ANG is critical for studying its enzymatic properties and biological roles.

Purpose of the Study:

• To achieve efficient heterologous production of human angiogenin (ANG) in Escherichia coli.
• To characterize the steady-state kinetic parameters of ANG's ribonucleolytic activity.
• To investigate the influence of pH and sodium ion concentration on ANG's catalytic efficiency and substrate binding.

Main Methods:

• Optimized heterologous protein expression in E. coli by replacing rare codons.
• Utilized hypersensitive fluorogenic substrates for continuous assay kinetic measurements.
• Determined kinetic parameters (k(cat)/K(M)) and analyzed pH-rate profiles and sodium ion dependency.

Main Results:

• Efficient production of active human ANG in E. coli was achieved.
• ANG exhibits classic bell-shaped pH-rate profiles with pK(1) = 5.0 and pK(2) = 7.0.
• Ribonucleolytic activity and substrate binding are highly sensitive to Na(+) concentration, with decreased Na(+) significantly increasing catalytic efficiency (k(cat)/K(M)).
• k(cat)/K(M) values increase with substrate length, indicating enhanced binding and/or turnover for longer RNA sequences.

Conclusions:

• The study successfully established a method for producing functional human ANG in E. coli.
• Detailed kinetic analysis reveals ANG's enzymatic activity is significantly modulated by environmental factors like pH and Na(+) concentration.
• Findings provide comprehensive insights into the substrate binding and catalytic mechanisms of angiogenin, crucial for its role in angiogenesis.