Distinct kinetic mechanisms of the two classes of Aminoacyl-tRNA synthetases.
Aminoacyl-tRNA synthetases are divided into two classes based on both functional and structural criteria. Distinctions between the classes have heretofore been based on general features, such as the position of aminoacylation on the 3'-terminal tRNA ribose, and the topology and tRNA-binding orientation of the active-site protein fold. Here we show instead that transient burst kinetics provides a distinct mechanistic signature dividing the two classes of tRNA synthetases, and that this distinction has significant downstream effects on protein synthesis. Steady-state and transient kinetic analyses of class I CysRS and ValRS, and class II AlaRS and ProRS, reveal that class I tRNA synthetases are rate-limited by release of aminoacyl-tRNA, while class II synthetases are limited by a step prior to aminoacyl transfer. The tight aminoacyl-tRNA product binding by class I enzymes correlates with the ability of EF-Tu to form a ternary complex with class I but not class II synthetases, and the further capacity of this protein to enhance the rate of aminoacylation by class I synthetases. These results emphasize that the distinct mechanistic signatures of class I versus class II tRNA synthetases ensure rapid turnover of aminoacyl-tRNAs during protein synthesis.
Zhang
Chun-Mei
CM
Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Perona
John J
JJ
Ryu
Kang
K
Francklyn
Christopher
C
Hou
Ya-Ming
YM
D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry / Q000145:classification / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008958:Models, Molecular; D010444:Peptide Elongation Factor Tu / Q000378:metabolism; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D046249:Transfer RNA Aminoacylation
D012329:RNA, Bacterial; D012346:RNA, Transfer, Amino Acyl; D010444:Peptide Elongation Factor Tu; D000604:Amino Acyl-tRNA Synthetases