Naslov
The origin of specificity and evolution of the synthetic and editing pathways in class I aaRSs

Autori
Dulić, Morana ; Cvetešić, Nevena ; Palencia, Andres ; Cusack, Stephen ; Gruić-Sovulj, Ita

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
10th International Symposium on Aminoacyl-tRNA Synthetases / - , 2015, 20-20

Skup
10th International Symposium on Aminoacyl-tRNA Synthetases

Mjesto i datum
Barcelona, Španjolska, 18.10.2015. - 22.10.2015

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
aminoacyl-tRNA synthetase; proofreading; pre-transfer editing; post-transfer editing

Sažetak
The inability of some aminoacyl-tRNA synthetases (aaRSs) to discriminate efficiently against structurally similar non-cognate amino acids in either step of the aminoacylation reaction prompted the evolution of hydrolytic proofreading. tRNAs have crucial roles in this process: i) aminoacylated tRNAs deliver amino acids to the post-transfer editing domain for proofreading, and ii) tRNA, in some cases, may organize the synthetic site and strengthen its capacity to hydrolyze aminoacyl-adenylates prior to the aminoacyl transfer step. Using class Ia isoleucyl- (IleRS) and leucyl-tRNA synthetases (LeuRS) from Escherichia coli as model proteins for the analysis of pre- and post-transfer editing mechanisms, respectively, we discovered that highly similar principles govern specificity in both editing pathways. Hydrolytic clearance of cognate Leu-tRNALeu at the LeuRS CP1 editing domain is precluded by a 103-fold decreased rate of deacylation as compared with that of misacylated tRNALeu, which requires proofreading. No substantial effect was observed on the binding affinity for aminoacylated tRNAs. This suggests that the committed post-transfer editing site excludes the cognate product predominately by mispositioning of the catalytic residues, not by operating as a steric sieve. Similar conclusions may be drawn for pre-transfer editing in which specificity of the synthetic site relies on kinetic partitioning that favors Ile-tRNAIle synthesis and encourages valyl- adenylate hydrolysis. Interestingly, in both cases it appears that tRNAs per se do not promote amino acid specificity. Our data indicate that aaRSs use fundamentally different mechanisms to strengthen specificity in the synthetic and editing pathways. While rejection of the non-cognate amino acid in the synthetic pathway is exercised through discrimination at ground state binding, specificity in the editing pathways predominantly relies on complementarity at the transition state. IleRS seems to be unique in exhibiting tRNA-dependent pre-transfer editing. To add to this puzzle, we now find that whereas the E. coli enzyme edits various non-cognate amino acids by the tRNA- dependent pre-transfer route, the synthetic sites of IleRSs of eukaryotic origin have apparently lost the capacity to operate in that way.

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Biologija

POVEZANOST RADA