Aminoacyl-transferases and the N-end rule pathway of prokaryotic/eukaryotic specificity in a human pathogen

doi:10.1073/pnas.0511224103

Aminoacyl-transferases and the N-end rule pathway of prokaryotic/eukaryotic specificity in a human pathogen

^†Division of Biology, California Institute of Technology, Pasadena, CA 91125; and
^‡National Research Laboratory of Molecular Microbial Pathogenesis and Genome Research Center for Enteropathogenic Bacteria, Chonnam National University Medical School, Gwangju 501-746, Korea

Contributed by Alexander Varshavsky, December 28, 2005

Abstract

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. Primary destabilizing N-terminal residues (Nd^p) are recognized directly by the targeting machinery. The recognition of secondary destabilizing N-terminal residues (Nd^s) is preceded by conjugation of an Nd^p residue to Nd^s of a polypeptide substrate. In eukaryotes, ATE1-encoded arginyl-transferases (R^D,E,C*-transferases) conjugate Arg (R), an Nd^p residue, to Nd^s residues Asp (D), Glu (E), or oxidized Cys residue (C*). Ubiquitin ligases recognize the N-terminal Arg of a substrate and target the (ubiquitylated) substrate to the proteasome. In prokaryotes such as Escherichia coli, Nd^p residues Leu (L) or Phe (F) are conjugated, by the aat-encoded Leu/Phe-transferase (L/F^K,R-transferase), to N-terminal Arg or Lys, which are Nd^s in prokaryotes but Nd^p in eukaryotes. In prokaryotes, substrates bearing the Nd^p residues Leu, Phe, Trp, or Tyr are degraded by the proteasome-like ClpAP protease. Despite enzymological similarities between eukaryotic R^D,E,C*-transferases and prokaryotic L/F^K,R-transferases, there is no significant sequelogy (sequence similarity) between them. We identified an aminoacyl-transferase, termed Bpt, in the human pathogen Vibrio vulnificus. Although it is a sequelog of eukaryotic R^D,E,C*-transferases, this prokaryotic transferase exhibits a “hybrid” specificity, conjugating Nd^p Leu to Nd^s Asp or Glu. Another aminoacyl-transferase, termed ATEL1, of the eukaryotic pathogen Plasmodium falciparum, is a sequelog of prokaryotic L/F^K,R-transferases (Aat), but has the specificity of eukaryotic R^D,E,C*-transferases (ATE1). Phylogenetic analysis suggests that the substrate specificity of R-transferases arose by two distinct routes during the evolution of eukaryotes.

Footnotes

^§To whom correspondence should be addressed. E-mail: avarsh{at}caltech.edu
Author contributions: E.G., R.-G.H., and A.V. designed research; E.G., R.-G.H., and K.P. performed research; E.G., K.P., J.H.R., E.M.S., and A.V. contributed new reagents/analytic tools; E.G., R.-G.H., K.P., J.H.R., E.M.S., and A.V. analyzed data; and E.G. and A.V. wrote the paper.
Conflict of interest statement: No conflicts declared.
Abbreviations:

Abbreviations:

aa-transferase,

aminoacyl-transferase;

Bpt,

bacterial protein transferase;

Ub,

ubiquitin;

Ndp,

primary destabilizing N-terminal residue;

Nds,

secondary destabilizing N-terminal residue;

C*,

oxidized cysteine residue;

βgal,

β-galactosidase.