Engineering ribonuclease A: production, purification and characterization of wild-type enzyme and mutants at Gln11.
Bovine pancreatic ribonuclease A (RNase A) has been the object of much landmark work in biological chemistry. Yet the application of the techniques of protein engineering to RNase A has been limited by problems inherent in the isolation and heterologous expression of its gene. A cDNA library was prepared from cow pancreas, and from this library the cDNA that codes for RNase A was isolated. This cDNA was inserted into expression plasmids that then directed the production of RNase A in Saccharomyces cerevisiae (fused to a modified alpha-factor leader sequence) or Escherichia coli (fused to the pelB signal sequence). RNase A secreted into the medium by S.cerevisiae was an active but highly glycosylated enzyme that was recoverable at 1 mg/l of culture. RNase A produced by E.coli was in an insoluble fraction of the cell lysate. Oxidation of the reduced and denatured protein produced active enzyme which was isolated at 50 mg/l of culture. The bacterial expression system is ideal for the large-scale production of mutants of RNase A. This system was used to substitute alanine, asparagine or histidine for Gln11, a conserved residue that donates a hydrogen bond to the reactive phosphoryl group of bound substrate. Analysis of the binding and turnover of natural and synthetic substrates by the wild-type and mutant enzymes shows that the primary role of Gln11 is to prevent the non-productive binding of substrate.
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002417:Cattle; D018076:DNA, Complementary / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015723:Gene Library; D005822:Genetic Vectors / Q000235:genetics; D005973:Glutamine / Q000235:genetics; D006031:Glycosylation; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D010179:Pancreas / Q000201:enzymology; D010957:Plasmids / Q000235:genetics; D015202:Protein Engineering / Q000379:methods*; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics
D018076:DNA, Complementary; D011994:Recombinant Proteins; D005973:Glutamine; D012259:Ribonuclease, Pancreatic