Naslov
Unusual homologs of atypical enzymes

Autori
Močibob, Marko ; Weygand-Đurašević, Ivana

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

Izvornik
Book of Abstracts of the HDBMB 2008, Congress of the Croatian Society of Biochemistry and Molecular Biology with international participation / Strelec, Ivica ; Glavaš-Obrovac, Ljubica - Osijek : Hrvatsko Društvo za Biotehnologiju, 2008, 112-112

ISBN
978-953-95551-2-0

Skup
HDBMB 2008, Congress of the Croatian Society of Biochemistry and Molecular Biology 2008

Mjesto i datum
Osijek, Hrvatska, 17.09.2008. - 20.09.2008

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
seryl-tRNA synthetase; amino acid activation

Sažetak
Aminoacyl-tRNA synthetases (aaRS) are enzymes required for protein biosynthesis, which catalyze attachment of cognate amino acids to corresponding tRNAs. They are considered to be essential, and evolutionarily well preserved. However, a small number of methanogenic archaea possess a distinctive type of seryl-tRNA synthetase (SerRS) which show low sequence homology to typical SerRSs found in other organisms from all three domains of life (including other archaea). Moreover, the crystal structure of SerRS from Methanosarcina barkeri revealed a completely different tRNA-binding domain, together with markedly different architecture of active site, containing zinc ion involved in serine binding. Therefore, these enzymes were termed atypical, or methanogenic-type, SerRS. Curiously, in some eubacterial genomes, a putative open reading frame homologous to the methanogenic-type SerRS lacking tRNA-binding domain can be found, together with canonical SerRS. We have cloned putative open reading frames homologous to catalytic core of methanogenic-type SerRS from Agrobacterium tumefaciens and Bradyrhizobium japonicum. Two hypothetical ORFs for methanogenic-type SerRS homologs can be found in B. japonicum genome. Preliminary biochemical characterization has shown that these proteins are homodimeric and they contain zinc, as expected from homology to methanogenic-type SerRS. Surprisingly, homolog from A. tumefaciens preferentially activates alanine, while preferred substrate for both B. japonicum homologs is glycine. A change in amino acid specificity was not anticipated, since substrate selectivity of aminoacyl-tRNA synthetases is usually evolutionary strongly preserved. Kinetic analysis revealed that B. japonicum homologs weakly activate alanine, while A. tumefaciens homolog is more promiscuous, capable of activating several other amino acids. Substrate binding (ATP, amino acid) appears to be ordered, with ATP binding first. Serine, weakly activated by homolog from A. tumefaciens, is not transferred to cognate tRNA. The final acceptor(s) of activated amino acids remain to be determined. The biological role of these unusual enzymes is unknown. Since there are few documented cases of aaRS duplications, homologs may represent atypical aaRS lacking (yet unidentified) tRNA-binding domain provided in trans. On the other hand, these enzymes may be adopted for biological process unrelated to protein biosynthesis since surveyed organisms do possess canonical aaRS.

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Biologija

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