Genetic selection for critical residues in ribonucleases

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Engineering

Background:

• Mammalian ribonucleases (RNases) are crucial enzymes with diverse biological roles.
• Understanding protein structure-function relationships is key to protein engineering and drug development.
• Bovine pancreatic ribonuclease (RNase A) and human angiogenin are homologous proteins with distinct functions.

Purpose of the Study:

• To identify residues critical for the structure and function of RNase A and angiogenin.
• To compare critical residues between homologous but functionally distinct proteins.
• To explore the evolutionary divergence within the RNase A superfamily.

Main Methods:

• Utilized error-prone polymerase chain reactions to introduce random mutations in RNase A and angiogenin genes.
• Employed a genetic selection strategy based on cytotoxicity to isolate inactive protein variants.
• Analyzed mutation data to determine residues intolerant to substitution.

Main Results:

• Identified 23 critical residues in RNase A and 29 in angiogenin.
• Found six residues (two histidine, four cysteine) wholly intolerant to substitution in both proteins.
• Discovered that most critical residues are buried in the hydrophobic core and tolerate only conservative substitutions.
• Observed a correlation between residue importance and sequence conservation, with some non-conserved residues also being critical.

Conclusions:

• This study pinpoints essential residues in RNase A and angiogenin, offering targets for future functional studies.
• The comparison of critical residues provides insights into the molecular evolution of the RNase A superfamily.
• The methodology can be applied to investigate other ribonucleases and protein families.