   2.3.2.6 | physiological function |
all Escherichia coli proteins initiate with formyl-methionine. Upon proteolytic cleavage by exo- and/or endopeptidases, a neo-N-terminus is exposed which is categorized into primary destabilizing (1°, including Leu, Phe, Trp, and Tyr) and secondary destabilizing (2°, including Arg and Lys) residues. 2° Degrons are recognized by the L/F transferase, which posttranslationally adds a Leu or Phe (1°) destabilizing residue from an aminoacyl-tRNA to the N-terminus of a protein having an Arg or Lys (2°). The adaptor ClpS recognizes and binds to proteins with a 1° N-degron and delivers the tagged protein to the proteasome-like complex ClpAP, where the protein is unfolded by the AAA+ ATPase ClpA and degraded by the protease ClpP. Posttranslational non-ribosomal amino acid transfer mechanism of L/F transferase transferring the aminoacyl moiety of the 3' end of an aminoacyl-tRNA substrate to an acceptor substrate, overview. The alpha-amino group of the N-terminus of a substrate polypeptide acts as a nucleophile and attacks the amino acyl carbonyl group. Two catalytic residues, D186 and Q188, are actively involved in the catalytic transfer reaction. The general base Q188, first activated by D186 via an electron-relay system, attracts a proteon from the alpha-NH3+ group of the N-terminal Arg acceptor substrate peptide and facilitates the nucleophile attack on the carbonyl carbon of the aminoacyl-tRNA donor substrate |
759102 |
