Steve Ealick's Research Group


Clostridium botulinum Thiaminase I


PDB file:

4KYS

Description:

Thiaminases catalyze the degradation of thiamin into its thiazole and pyrimidine components.  Clostridium botulinum (Cb) thiaminase I has 51% identity to Bacillus thiaminolyticus (Bt) thiaminase I, the structure of which we had determined previously; however, this is the first structure of a thiaminase I/substrate complex. This structure of the inactive C143S mutant of provided atomic level details of the orientation of thiamin upon binding, which enabled us to determine the active site residues involved in substrate binding and catalysis. Cb thiaminase I is a member of the group II perisplasmic binding family as are TbpA, Thi5 and ThiY, all of which we have explored in our studies of thiamin biosynthesis and degradation.

The active form of Cb thiaminase is as a monomer. Like other members of the group II periplasmic binding protein superfamily, and can be divided into two distinct domains as shown at the right.


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Each monomer contains one thiamin molecule in a V-shaped cleft between the two domains as indicated above.  Six tyrosine residues, Tyr46, Tyr48, Tyr80, Tyr252, Tyr269, and Tyr300 only some of which are shown for clarity,, form an outer collar of the cleft with most of the active site residues located at the bottom of the cleft.  The catalytic cysteine residue Cys143, which is represented by Ser143 in the C143S/thiamin complex is well positioned to interact with thiamin.


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Reference:

Sikowitz MD, Shome B, Zhang Y, Begley TP, and Ealick SE. Structure of a Clostridium botulinum C143S thiaminase I/thiamin complex reveals active site architecture. Biochemistry 52:7830−7839 (2013). PubMed



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