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The Characterization Of Trna Modifying Enzymes S-Adenosylmethionine : Trna Ribosyltransferase-Isomerase (Quea) And A Novel Type I Gtp Cyclohydrolase, Shilah Amal Bonnett
The Characterization Of Trna Modifying Enzymes S-Adenosylmethionine : Trna Ribosyltransferase-Isomerase (Quea) And A Novel Type I Gtp Cyclohydrolase, Shilah Amal Bonnett
Dissertations and Theses
Queuosine is a hypermodified nucleoside located in the wobble position of bacterial and eukaryotic tRNAs coding for Asp, Tyr, His and Asn. The biosynthesis involves the participation of S-adenosyl-methionine:tRNA ribosyltransferase-isomerase (QueA) and a GTP Cyclohydrolase-I. QueA catalyzes the transfer and isomerization of the ribosyl moiety from AdoMet to preQ1 modified tRNA. Substrate analogs of AdoMet were used to elucidate important substrate-enzyme interactions and to test key steps in the proposed chemical mechanism. Replacing AdoMet with SeAdoMet had little effect upon substrate binding but exhibited 30-fold reduction in kcat, consistent with deprotonation at C-5' as the first catalytic step. 7-deazaAdoMet failed …