J. Biol. Chem., Vol. 260, Issue 6, 3350-3354, 03, 1985
Identification of a trpG-related glutamine amide transfer domain in Escherichia coli GMP synthetase
H Zalkin, P Argos, SV Narayana, AA Tiedeman and JM Smith
An improved method was developed to align related protein sequences and
search for homology. A glutamine amide transfer domain was identified in an
NH2-terminal segment of GMP synthetase from Escherichia coli. Amino acid
residues 1-198 in GMP synthetase are homologous with the glutamine amide
transfer domain in trpG X D-encoded anthranilate synthase component
II-anthranilate phosphoribosyltransferase and the related pabA-encoded
p-aminobenzoate synthase component II. This result supports a model for
gene fusion in which a trpG-related glutamine amide transfer domain was
recruited to augment the function of a primitive NH3-dependent GMP
synthetase. Sequence analyses emphasize that glutamine amide transfer
domains are thus far found only at the NH2 terminus of fused proteins. Two
rules are formulated to explain trpG and trpG-related fusions. (i) trpG and
trpG-related genes must have translocated immediately up-stream of genes
destined for fusion in order to position a glutamine amide transfer domain
at the NH2 terminus after fusion. (ii) trpG and trpG-related genes could
not translocate adjacent to a regulatory region at the 5' end of an operon.
These rules explain known trpG-like fusions and explain why trpG and pabA
are not fused to trpE and pabB, respectively. Alignment searches of GMP
synthetase with two other enzymes that bind GMP, E. coli
amidophosphoribosyltransferase and human hypoxanthine-guanine
phosphoribosyltransferase, suggest a structurally homologous segment which
may constitute a GMP binding site.