The peptide bonds preceding Pro 93 and Pro 114 of bovine pancreatic ribonuclease A (RNase A) are in the cis conformation. The trans-to-cis isomerization of these bonds had been indicted as the slow step during protein folding. Here, site-directed mutagenesis was used to replace Pro 93 or Pro 114 with a glycine residue, and the crystalline structure of the P93G variant was determined by X-ray diffraction analysis to a resolution of 1.7 A. This structure is essentially identical to that of the wild-type protein, except for the 91-94 beta-turn containing the substitution. In the wild-type protein, the beta-turn is of type VIa. In the P93G variant, this turn is of type II with the peptide bond preceding Gly 93 being trans. The thermal stabilities of the P93G and P114G variants were assessed by differential scanning calorimetry and thermal denaturation experiments monitored by ultraviolet spectroscopy. The value of delta deltaGm which reports on the stability lost in the variants, is 1.5-fold greater for the P114G variant than for the P93G variant. The greater stability of the P93G variant is likely due to the relatively facile accommodation of residues 91-94 in a type II turn, which has a preference for a glycine residue in its i + 2 position. Study holds ProTherm entries: 3220, 3221, 3222, 3223, 3224, 3225, 14158, 14159, 14160, 14161 Extra Details: beta-turn; cis proline; endonuclease; protein stability;,ribonuclease A; X-ray crystallography
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:21 p.m.
|Number of data points||14|
|Proteins||Ribonuclease pancreatic ; Ribonuclease pancreatic|
|Assays/Quantities/Protocols||Experimental Assay: ddG ionic:-: -, temp:61.8 C ; Experimental Assay: ddG ionic:NaCl: 0.10 M, temp:61.6 C ; Experimental Assay: dTm ionic:: ; Experimental Assay: Tm ionic:: , buffers:Sodium acetate-: 30 mM ; Experimental Assay: Tm ionic:: , buffers:Sodium acetate: 30 mM ; Experimental Assay: dTm ionic:NaCl: 0.10 M ; Experimental Assay: Tm buffers:Sodium acetate: 30 mM, ionic:NaCl: 0.10 M ; Derived Quantity: dTm ionic:: , buffers:Sodium acetate-: 30 mM|
|Libraries||Mutations for sequence KETAAAKFERQHMDSSTSAASSSNYCNQMMKSRNLTKDRCKPVNTFVHESLADVQAVCSQKNVACKNGQTNCYQSYSTMSITDCRETGSSKYPNCAYKTTQANKHIIVACEGNPYVPVHFDASV|