A chemically synthesized gene for ribonuclease A has been expressed in Escherichia coli using a T7 expression system (Studier, F.W., Rosenberg, A.H., Dunn, J.J., & Dubendorff, J.W., 1990, Methods Enzymol. 185, 60-89). The expressed protein, which contains an additional N-terminal methionine residue, has physical and catalytic properties close to those of bovine ribonuclease A. The expressed protein accumulates in inclusion bodies and has scrambled disulfide bonds; the native disulfide bonds are regenerated during purification. Site-directed mutations have been made at each of the two cis proline residues, 93 and 114, and a double mutant has been made. In contrast to results reported for replacement of trans proline residues, replacement of either cis proline is strongly destabilizing. Thermal unfolding experiments on four single mutants give delta Tm approximately equal to 10 degrees C and delta delta G0 (apparent) = 2-3 kcal/mol. The reason is that either the substituted amino acid goes in cis, and cis<==>trans isomerization after unfolding pulls the unfolding equilibrium toward the unfolded state, or else there is a conformational change, which by itself is destabilizing relative to the wild-type conformation, that allows the substituted amino acid to form a trans peptide bond. Study holds ProTherm entries: 2137, 2138, 2139, 2140, 2141, 2142, 13934, 13935, 13936, 13937, 13938 Extra Details: cis peptide bond; cis proline mutants; ribonuclease A;,thermal stability
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:18 p.m.
|Number of data points||22|
|Proteins||Ribonuclease pancreatic ; Ribonuclease pancreatic|
|Assays/Quantities/Protocols||Experimental Assay: dCp ; Experimental Assay: ddG ; Experimental Assay: Tm ; Derived Quantity: dTm|
|Libraries||Mutations for sequence KETAAAKFERQHMDSSTSAASSSNYCNQMMKSRNLTKDRCKPVNTFVHESLADVQAVCSQKNVACKNGQTNCYQSYSTMSITDCRETGSSKYPNCAYKTTQANKHIIVACEGNPYVPVHFDASV|