A model for the Bacillus subtilis formylglycinamide ribonucleotide amidotransferase multiprotein complex

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Formylglycinamide ribonucleotide amidotransferase (FGAR-AT) is essential for purine biosynthesis.
• PurL exists in large (lgPurL) and small (smPurL) forms, with smPurL requiring PurS and PurQ for activity.
• PurS and PurQ's roles in the smPurL-dependent pathway were not fully understood.

Purpose of the Study:

• To determine the structure of Bacillus subtilis PurS.
• To elucidate the quaternary structure of PurS.
• To model the PurS/smPurL/PurQ complex for understanding purine biosynthesis.

Main Methods:

• X-ray crystallography was used to determine the structure of PurS in two crystal forms (P2(1) and C2).
• Homology modeling was employed, using the determined PurS structure and existing lgPurL structure.
• The HisH domain of imidazole glycerol phosphate synthetase served as a model for PurQ.

Main Results:

• The crystal structures revealed PurS forms a dimer with a central beta-sheet and four flanking helices.
• PurS exists as a tetramer in both crystal forms, with dimers interacting via C-terminal regions to form a beta-barrel.
• A homology model of the PurS/smPurL/PurQ complex was constructed, suggesting stoichiometry and placing conserved residues at active sites.

Conclusions:

• The structure of PurS provides insights into its role in the purine biosynthetic pathway.
• The modeled PurS/smPurL/PurQ complex is consistent with biochemical data.
• Understanding the structure and complex formation is key to elucidating the mechanism of purine synthesis.