1ygb

From Proteopedia

Crystal Structure of the catalytic fragment of alanyl-tRNA synthetase in complex with L-serine

Structural highlights

1ygb is a 1 chain structure with sequence from Aquifex aeolicus. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:	X-ray diffraction, Resolution 2.48Å
Ligands:
Resources:	FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

Function

SYA_AQUAE Catalyzes the attachment of alanine to tRNA(Ala) in a two-step reaction: alanine is first activated by ATP to form Ala-AMP and then transferred to the acceptor end of tRNA(Ala). Also edits incorrectly charged Ser-tRNA(Ala) and Gly-tRNA(Ala) via its editing domain (By similarity).[HAMAP-Rule:MF_00036]

Evolutionary Conservation

Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.

Publication Abstract from PubMed

The genetic code is fixed in aminoacylation reactions catalyzed by aminoacyl-tRNA synthetases. Amino acid discrimination occurs at two sites: one for amino acid activation and aminoacylation and one for editing misactivated amino acids. Although the active site sieves out bulkier amino acids, misactivation occurs with substrates whose side chains are smaller than the cognate one. Paradoxically, although alanyl-tRNA synthetase activates glycine as well as alanine, the sterically larger (than alanine) serine is also misactivated. Here, we report crystal structures of an active fragment of Aquifex aeolicus alanyl-tRNA synthetase complexed, separately, with Mg2+-ATP, alanine, glycine, and serine. Ala and Gly are bound in similar orientations in a side-chain-accommodating pocket, where alpha-amino and carboxyl groups are stabilized by salt bridges, and the carboxyl by an H-bond from the side chain NH2 of Asn-194. In contrast, whereas the same two salt bridges stabilize bound Ser, H-bonding of the highly conserved (among class II tRNA synthetases) Asn-194 side chain NH2 to the Ser OH, instead of to the carboxyl, forces pocket expansion. Significantly, in the Mg2+-ATP complex, Asn-194 coordinates a Mg2+-alpha-phosphate bridge. Thus, the sieve for Ser exclusion is broken because of selective pressure to retain Asn-194 for Mg2+-ATP and Ala binding.

Breaking sieve for steric exclusion of a noncognate amino acid from active site of a tRNA synthetase.,Swairjo MA, Schimmel PR Proc Natl Acad Sci U S A. 2005 Jan 25;102(4):988-93. Epub 2005 Jan 18. PMID:15657145^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

References

↑ Swairjo MA, Schimmel PR. Breaking sieve for steric exclusion of a noncognate amino acid from active site of a tRNA synthetase. Proc Natl Acad Sci U S A. 2005 Jan 25;102(4):988-93. Epub 2005 Jan 18. PMID:15657145