Sua5 is required for the formation of threonylcarbamoyl group on the adenosine
at position 37(t6A37) in almost all tRNAs decoding ANN codons (
Pichard-Kostuch et al. 2018). It likely catalyzes
the condensation of L-threonine bicarbonate (HCO-3) and ATP
to give threonylcarbamoyl-AMP (TC-AMP).
KEOPS/EKC complex is a tRNA modification complex involved in the biosynthesis of
N6-threonylcarbamoyl adenosine (t6) (
Wan et al. 2017).
In arachaea and eukaryotes, KEOPS/EKC is composed of OSGEP/Kae1, PRPK/Bud32,
TPRKB/Cgi121, and LAGE3/PCC1.Fungi contains an additional subbunit, Gon7, whose orthologues
in other species, if present, remain unidentified.
Together with Sua5, they catalyze the in vivo formation of t6.
Structurally,Sua5 displays a YrdC-like domain between A50 and G250.
The yrdC-like domain is typically an ~185-residue module which can be found in stand-alone form
(
YrdC-like) ,
or in association with other domains such as the acylphosphatase-like domain which
catalyzes the hydrolysis of various acyl phosphate carboxyl-phosphate bonds such as
carbamyl phosphate, succinyl phosphate, 1,3-diphosphoglycerate, etc (
YrdC-like).The yrdC-like domain
features a large concave surface on one side that exhibits a positive electrostatic potential.
The dimension of this depression, its curvature, and the fact that conserved basic amino acids are
located at its floor suggest that it may be a nucleic acid binding domain.