Aminoacyl-tRNA synthetases (EC 6.1.1.-)  are a group of enzymes which
activate amino acids and transfer them to specific tRNA molecules as the first
step in protein biosynthesis. In prokaryotic organisms there are at least
twenty different types of aminoacyl-tRNA synthetases, one for each different
amino acid. In eukaryotes there are generally two aminoacyl-tRNA synthetases
for each different amino acid: one cytosolic form and a mitochondrial form.
While all these enzymes have a common function, they are widely diverse in
terms of subunit size and of quaternary structure.
A few years ago it was found  that several aminoacyl-tRNA synthetases share
a region of similarity in their N-terminal section, in particular the
consensus tetrapeptide His-Ile-Gly-His ('HIGH') is very well conserved. The
'HIGH' region has been shown  to be part of the adenylate binding site. The
'HIGH' signature has been found in the aminoacyl-tRNA synthetases specific for
arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine,
tyrosine, tryptophan, and valine. These aminoacyl-tRNA synthetases are
referred to as class-I synthetases [4,5,6] and seem to share the same tertiary
structure based on a Rossmann fold.
In position 8 of the pattern His is present in all tRNA-synthetases of
class-I except in some bacterial tryptophanyl-tRNA synthetases which have a
Thr in that position.
PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and
distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives
(CC BY-NC-ND 4.0) License, see prosite_license.html.