Steve Ealick's Research Group

Bacillus halodurans ThiY

PDB file:



The ATP-binding cassette transporter system ThiXYZ transports N-formyl-4-amino-5-aminomethyl-2-methylpyrimidine (FAMP), a thiamin salvage pathway intermediate, into cells. FAMP is then converted to 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) and recycled into the thiamin biosynthetic pathway. ThiY is the periplasmic substrate binding protein of the ThiXYZ system and delivers the substrate FAMP to the transmembrane domain. ThiY is also structurally homologous to thiamin binding protein (TbpA) and to thiaminase-I.

ThiY belongs to the group II periplasmic binding protein (PBP) family. The monomer is comprised of two domains. Domain 1 is a three layer αβα sandwich comprised of a mixed β-sheet of five β-strands, flanked by ten α-helices and one 310-helix. Domain 2 is a three layer αβα sandwich comprised of a mixed β-sheet containing five β-strands flanked by three α-helices and four 310-helices.


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The enzyme crystallizes as a tightly packed dimer with monomers related by noncrystallographic twofold symmetry.  The dimer interface is primarily hydrophilic and stabilized by extensive hydrogen bonding.

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The ligand binding site of ThiY is located in a cleft between domain 1 and domain 2. FAMP was added during crystallization and was bound in the crystal structure.  

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Bale S, Rajashankar KR, Perry K, Begley TP, and Ealick SE. HMP Binding Protein ThiY and HMP-P Synthase Thi5 Are Structural Homologues. Biochemistry 49:8929-8936 (2010). PubMed

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