Zinc-mediated amino acid discrimination in cysteinyl-tRNA synthetase.
Escherichia coli cysteinyl-tRNA synthetase (CysRS) achieves a high level of amino acid specificity without an editing reaction. The crystal structure of CysRS bound to substrate cysteine suggested that direct thiol coordination to a tightly bound zinc ion at the base of the active site is the primary determinant of selectivity against non-cognate amino acids. This hypothesis has now been supported by spectroscopic studies of cobalt-substituted CysRS. Binding of cysteine, but not non-cognate amino acids, induces high absorption in the ligand-to-metal charge transfer region, providing evidence for formation of a metal-thiolate bond. In addition, mutations in the zinc ligands alter the absorption spectrum without reducing the discrimination against non-cognate amino acids. These results argue strongly for a major role for the zinc ion in amino acid discrimination by CysRS, where the tight zinc-thiolate interaction and the strict structural geometry of the metal ion are sufficient to reject serine by more than 20,000-fold at the binding step.
Zhang
Chun-Mei
CM
Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, 233 S 10th Street, BLSB 222, Philadelphia, PA 19107, USA.
Christian
Thomas
T
Newberry
Kate J
KJ
Perona
John J
JJ
Hou
Ya-Ming
YM
D000596:Amino Acids / Q000737:chemistry*; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology; D008958:Models, Molecular; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry*; D012694:Serine / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry*
D000596:Amino Acids; D012346:RNA, Transfer, Amino Acyl; D012694:Serine; D000604:Amino Acyl-tRNA Synthetases; D015032:Zinc