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Structural investigation of catalytically modified F120L and F120Y semisynthetic ribonucleases
Author(s) -
Demel V. Srini J.,
Doscher Marilynn S.,
Glinn Michele A.,
Martin Philip D.,
Ram Michal L.,
Edwards Brian F.P.
Publication year - 1994
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560030106
Subject(s) - phenylalanine , stereochemistry , chemistry , cytidine , active site , hydrogen bond , tyrosine , enzyme , phosphate , uridine , leucine , molecule , rna , biochemistry , amino acid , organic chemistry , gene
The structures of two catalytically modified semisynthetic RNases obtained by replacing phenylalanine 120 with leucine and tyrosine have been determined and refined at a resolution of 2.0 Å ( R = 0.161 and 0.184, respectively). These structures have been compared with the refined 1.8‐Å structure (R = 0.204) of the fully active phenylalanine‐containing enzyme (Martin PD, Doscher MS, Edwards BFP, 1987, J Biol Chem 262 :15930‐15938) and with the catalytically defective D121A (2.0 Å, R = 0.172) and D121N (2.0 Å, R = 0.186) analogs (deMel VSJ, Martin PD, Doscher MS, Edwards BFP, 1992, J Biol Chem 267 :247‐256). The movement away from the active site of the loop containing residues 65‐72 is seen in all three catalytically defective analogs‐F120L, D121A, and D121N‐but not in the fully active (or hyperactive) F120Y. The insertion of the phenolic hydroxyl of Tyr 120 into a hydrogen‐bonding network involving the hydroxyl group of Ser 123 and a water molecule in F120Y is the likely basis for the hyperactivity toward uridine 2′,3′‐cyclic phosphate previously found for this analog (Hodges RS, Merrifield RB, 1974, Int J Pept Protein Res 6 :397‐405) as well as the threefold increase in K M for cytidine 2′,3′‐cyclic phosphate found for this analog by ourselves.