3NM3

The Crystal Structure of Candida glabrata THI6, a Bifunctional Enzyme involved in Thiamin Biosyhthesis of Eukaryotes

Summary for 3NM3

• Entry DOI: 10.2210/pdb3nm3/pdb
• Related: 3NL2 3NL3 3NL5 3NL6 3NM1
• Descriptor: Thiamine biosynthetic bifunctional enzyme, MAGNESIUM ION, THIAMIN PHOSPHATE, ... (4 entities in total)
• Functional Keywords: thi6, bifunctional enzyme, thiamin biosynthesis, eukaryoyes, transferase
• Biological source: Candida glabrata (yeast)
• Total number of polymer chains: 6
• Total formula weight: 352033.22

Authors

Paul, D.,Chatterjee, A.,Begley, T.P.,Ealick, S.E. (deposition date: 2010-06-21, release date: 2010-11-10, Last modification date: 2024-02-21)

Primary citation

Paul, D.,Chatterjee, A.,Begley, T.P.,Ealick, S.E.
Domain Organization in Candida glabrata THI6, a Bifunctional Enzyme Required for Thiamin Biosynthesis in Eukaryotes .
Biochemistry, 49:9922-9934, 2010

PubMed Abstract: THI6 is a bifunctional enzyme found in the thiamin biosynthetic pathway in eukaryotes. The N-terminal domain of THI6 catalyzes the ligation of the thiamin thiazole and pyrimidine moieties to form thiamin phosphate, and the C-terminal domain catalyzes the phosphorylation of 4-methyl-5-hydroxyethylthiazole in a salvage pathway. In prokaryotes, thiamin phosphate synthase and 4-methyl-5-hydroxyethylthiazole kinase are separate gene products. Here we report the first crystal structure of a eukaryotic THI6 along with several complexes that characterize the active sites responsible for the two chemical reactions. THI6 from Candida glabrata is a homohexamer in which the six protomers form a cage-like structure. Each protomer is composed of two domains, which are structurally homologous to their monofunctional bacterial counterparts. Two loop regions not found in the bacterial enzymes provide interactions between the two domains. The structures of different protein-ligand complexes define the thiazole and ATP binding sites of the 4-methyl-5-hydroxyethylthiazole kinase domain and the thiazole phosphate and 4-amino-5-hydroxymethyl-2-methylpyrimidine pyrophosphate binding sites of the thiamin phosphate synthase domain. Our structural studies reveal that the active sites of the two domains are 40 Å apart and are not connected by an obvious channel. Biochemical studies show 4-methyl-5-hydroxyethylthiazole phosphate is a substrate for THI6; however, adenosine diphospho-5β-ethyl-4-methylthiazole-2-carboxylic acid, the product of THI4, is not a substrate for THI6. This suggests that an unidentified enzyme is necessary to produce the substrate for THI6 from the THI4 product.

PubMed: 20968298
DOI: 10.1021/bi101008u

Experimental method

X-RAY DIFFRACTION (3.102 Å)