Steve Ealick's Research Group
Escherichia coli Thiamin Binding Protein
Thiamin deficiency can lead to several disorders including beriberi and Wernicke-Korsakoff syndrome creating an interest in thiamin transport and biosynthesis. ATP binding cassette (ABC) transporters are responsible for the transport of a wide variety of water soluble molecules and ions into prokaryotic cells. In gram negative bacteria, the periplasmic binding proteins (PBP) transport the ions or molecule to the ABC transporter. The crystal structure of a thiamin PBP from gene TbpA of E. coli was determined to 2.25 Å and found to belong to the group II PBP family. One interesting hit from the DALI server is thiaminase-I. Comparisons of TbpA and thiaminase-I topologies reveal a structural similarity between the two proteins, especially in domain 1 which contains the N-terminus. While the overall topology is similar, the binding of thiamin is not similar, suggesting that TbpA and thiaminase-I may be examples of divergent evolution.
The TbpA structure resembles other PBP’s and consists of two domains linked by flexible hinge region with a binding cleft which is approximately 6 Å wide, 17 Å long, and 12 Å deep, located between the two domains. A thiamin monophosphate (TMP) was found in each protomer
|The four monomers in the asymmetric unit are arranged as a pair of non-crystallographic dimers with chains A and B forming one dimer and chains C and D forming the second dimer. This dimer is most likely an artifact of crystallization and not physiologically relevant since dimer formation blocks access to the TMP binding site|
The thiamin binding site is located in a deep cleft
between domains 1 and 2 with the two crossovers between the domains blocking
one end of the cleft.
Soriano EV, Rajashankar KR, Hanes JW, Bale S, Kinsland C, Begley TP, and Ealick SE.Crystal Structure of TbpA, a Periplasmic Thiamin Transporter from Escherichia coli. Biochemistry 47:1346-1357 (2008).