Steve Ealick's Research Group

Methanococcus igneus Thiazole Synthase

PDB file:



Thiazole synthase Thi4 from Methanococcus igneus (MiThi4) has similarities to thiazole synthase from yeast and plants. We had previously determined the structure of S. cerevisiae thiazole synthase (ScThi4), which is a suicide thiazole synthase that uses a conserved Cys205 residue as the sulfur source, and determined that the sulfur transfer reaction is Fe(II) dependent. MiThi4 shows striking similarity to ScThi4, with all active site residues conserved except for a key cysteine residue, which in S. cerevisiae is the source of the thiazole sulfur atom. Our structure of MiThi4, in conjunction with the C205S variant of thiazole synthase from S. cerevisiae and the structure of the ortholog from Methanocaldococcus jannachii thiazole synthase (MjThi4), helps reveal the structural basis for the iron-dependent mechanism of sulfur transfer in archael and yeast thiazole synthases.

Each MiThi4 protomer consists of 12 β-strands organized as one six-stranded and two three stranded β-sheets flanked by nine α-helices.

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MiThi4 crystallizes as a pair of octamers in the asymmetric unit. The octamer is formed by the assembly of four closely packed dimers with 422 symmetry. The buried dimer face has an area of about ~1500 Å2 of surface area on each protomer. The octamer contains a channel along the fourfold axis with a maximum opening of about 30 Å.

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The active site of MiThi4 is located near the central channel and involves two adjacent protomers.  Most of the residues come from one protomer, and a loop containing Gly162-Asp166 from a fourfold related protomer completes the active site. The active site (left) and iron binding site (right) are shown in the model.

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Zhang X, Eser BE, Chanani PK, Begley TP, and Ealick SE. Structural Basis for Iron-mediated Sulfur Transfer in Archael and Yeast Thiazole Synthases. Biochemistry [Epub ahead of print]:(2016). PubMed

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