Phenylalanyl-tRNA synthetase from yeast and its discrimination of 19 amino acids in aminoacylation of tRNA(Phe)-C-C-A and tRNA(Phe)-C-C-A(3'NH2).
For discrimination between phenylalanine and 18 other naturally occurring non-cognate amino acids by the class II aminoacyl-tRNA synthetase specific for phenylalanine, discrimination factors, D, of 190-6300 have been determined from kcal and K(m) values. Generally, phenylalanyl-tRNA synthetase is more specific than the class II enzymes specific for Lys and Thr, but works with lower accuracy than the class I enzymes specific for IIe, Tyr, and Arg. In aminoacylation of tRNA(Phe)-C-C-A(3'NH2) discrimination factors D1 vary between 80-1610. Pre-transfer proof-reading factors II1 are in the range 2.3-74, post-transfer proof-reading factors II2 in the range 1.0-4.6, showing that pre-transfer proof-reading is the main correction step, post-transfer proofreading is less effective or negligible. Initial discrimination factors (I1 and I2) caused by differences in Gibbs free energies of binding between phenylalanine and non-cognate amino acids have been calculated assuming a two-step binding process. Factors I1 can be related to hydrophobic-interaction forces depending on accessible surface areas of the amino acids, factors I2 scatter about a low mean value and do not show any relation to amino acid structures or surfaces, indicating less checking of amino acid side chains in the putative second binding step.
Freist
W
W
Max-Planck-Institut für experimentelle Medizin, Göttingen, Germany.
Sternbach
H
H
Cramer
F
F
D000215:Acylation; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D007700:Kinetics; D010652:Phenylalanine-tRNA Ligase / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity; D013816:Thermodynamics
D000596:Amino Acids; D010652:Phenylalanine-tRNA Ligase