X-ray absorption spectroscopy of the zinc site in tRNA-guanine transglycosylase from Escherichia coli

Biochemistry
G A GarciaJ E Penner-Hahn

Abstract

A key step in the post-transcriptional modification of tRNA with queuine in Escherichia coli is the exchange of the queuine precursor, preQ1 into tRNA. This reaction is catalyzed by tRNA-guanine transglycosylase (TGT). We have previously shown that the E. coli TGT is a zinc metalloprotein [Chong et al. (1995) Biochemistry 34, 3694-3701]. Site-directed mutagenesis studies indicated that cysteines 302, 304, 307 and histidine 317 constitute the four ligands to the zinc. The involvement of histidine 317 is somewhat confounded by the presence of histidine 316. We have examined the zinc site in TGT (wt) and TGT (H317C) by X-ray absorption spectroscopy. The TGT (wt) data are most consistent with a tetracoordinate zinc with one nitrogen and three sulfur ligands. Interestingly, the data for TGT (H317C) are also consistent with a tetracoordinate zinc with one nitrogen and three sulfur ligands. The outer shell imidazole scattering for TGT (H317C) appears to be somewhat more ordered than that for TGT (wt), consistent with our previous suggestion that the wild-type enzyme may exist in two conformations the predominant one involving histidine 317 liganding to the zinc and the minor conformer involving histidine 316 liganding to the zinc. The...Continue Reading

Citations

Apr 17, 2003·Bioorganic Chemistry·Dirk Iwata-Reuyl
Jul 17, 1998·Current Opinion in Chemical Biology·V L Schramm
May 13, 2005·Bioorganic Chemistry·George A Garcia, Jeffrey D Kittendorf
Oct 11, 2001·Molecular Genetics and Metabolism·R C Morris, M S Elliott
Aug 1, 2009·EcoSal Plus·Dietrich H Nies, Gregor Grass

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