UVM Theses and Dissertations
Format:
Print
Author:
Hyde, Samantha J.
Dept./Program:
Microbiology and Molecular Genetics
Year:
2012
Degree:
PhD
Abstract:
TRNAHis guanylyltransferase (Thg1) is a highly unusual enzyme, in that, unlike traditional polymerases, it catalyzes nucleotide extension in a 3' to 5' direction (Jackman & Phizicky 2006a). Thg1 family members are the only enzymes known to possess this ability. It was therefore highly surprising that the first crystal structure of a member of this family of enzymes, human tRNAHis guanylyltransferase (hTHG1), revealed an active site that closely resembles that found in traditional polymerases (Hyde et al. 2010). The major function of Thg1 family members is known in eukaryotes: it adds a guanine nucleotide to the 5' end of tRNAHis molecules.
This G₁ guanine is a critical recognition element for histidy1-tRNA synthetase. However, since prokaryotes encode this guanine in the gene for tRNAHis, it is surprising to find that there are Thg1 homologs present in some prokaryotic and archaeal species. New evidence suggest that these homologs (Thg1-like proteins or TLP) play a more generalized role in 5' tRNA end repair (Abad et al. 2011). We present the first crystal structure of a bacterial TLP bound to ATP or GTP, which are two nucleotide substrates for this family of enzymes. The enzyme is a tetramer like its human counterpart, with which it share substantial structural similarity.
This G₁ guanine is a critical recognition element for histidy1-tRNA synthetase. However, since prokaryotes encode this guanine in the gene for tRNAHis, it is surprising to find that there are Thg1 homologs present in some prokaryotic and archaeal species. New evidence suggest that these homologs (Thg1-like proteins or TLP) play a more generalized role in 5' tRNA end repair (Abad et al. 2011). We present the first crystal structure of a bacterial TLP bound to ATP or GTP, which are two nucleotide substrates for this family of enzymes. The enzyme is a tetramer like its human counterpart, with which it share substantial structural similarity.