CRYSTAL-STRUCTURE AT 1.2 ANGSTROM RESOLUTION AND ACTIVE-SITE MAPPING OF ESCHERICHIA-COLI PEPTIDYL-TRANSFER-RNA HYDROLASE

Peptidyl-tRNA hydrolase activity from Escherichia coli ensures the rec ycling of peptidyl-tRNAs produced through abortion of translation, Thi s activity, which is essential for cell viability, is carried out by a monomeric protein of 193 residues, The structure of crystalline pepti dyl-tRNA hydrolase could be solved at 1.2 Angstrom resolution, It indi cates a single alpha/beta globular domain built around a twisted mixed beta-sheet, similar to the central core of an aminopeptidase from Aer omonas proteolytica, This similarity allowed the characterization by s ite-directed mutagenesis of several residues of the active site of pep tidyl-tRNA hydrolase, These residues, strictly conserved among the kno wn peptidyl-tRNA hydrolase sequences, delineate a channel which, in th e crystal, is occupied by the C-end of a neighbouring peptidyl-tRNA hy drolase molecule, Hence, several main chain atoms of three residues be longing to one peptidyl-tRNA hydrolase polypeptide establish contacts inside the active site of another peptidyl-tRNA hydrolase molecule, Su ch an interaction is assumed to represent the formation of a complex b etween the enzyme and one product of the catalysed reaction.