Steve Ealick's Research Group

Thiaminase-I from Bacillus thiaminolyticus

PDB files:

2THI (Form I, chains A and B)

3THI (Form II, chain A)

4THI (Form II, with bound inhibitor: 4-amino-6-chloro-2,5-dimethylpyrimidine)


Two thiaminases, which catalyze the degredation of thiamin (vitamin B1) have been isolated. Thiaminase-I catalyzes a reaction in which thiazole is replaced by a variety of organic nucleophiles, while thiaminase-II uses water as the nucleophile. In this paper, we determined the structure of thiaminase-I in two crystal forms (I and II) as well as the structure of form II with an inhibitor. In addition, we proposed a double addition-elimination reaction as the mechanism of action.

Thi-I is a monomer in its biological active form, with two distinct globular domains (the N-domain and the C domain). This structure was also determined at 2.0 Å resolution by molecular replacement. This image shows Form II of thiaminase-I with the inhibitor 4-amino-2,5-dimethylpyrimidine covalently bonded to C113. This analogue, which functions as a mechanism-based inactivating agent, confirms the location of the active site.


Click the image to enlarge.

The active site lies in a cleaft between the N-domain and the C-domain. The structure clearly shows C113 bonding to the pyrimidine. E241 is a possible active site base involved in deprotonation of Cys113, as evidenced by the inactivity of the E241G mutant.

Click the image to enlarge.



Campobasso N, Costello CA, Kinsland C, Begley TP, and Ealick SE. Crystal Structure of Thiaminase-I from Bacillus thiaminolyticus at 2.0 Å Resolution. Biochemistry 37:15981-15989 (1998).

Campobasso N., Begun J., Costello CA, Begley TP and Ealick SE. Crystallization and Preliminary X-ray Analysis of Thiaminase I from Bacillus thiaminolyticus: Space Group Change Upon Freeing of Crystals. Acta Crystallogr. D 54:448-450 (1998).

Contacts Procedures Structures Projects Publications Lab Home Page Group Members