title: Structural basis for pH dependent monomer-dimer transition of 3,4-dihydroxy 2-butanone-4-phosphate synthase domain from Mycobacterium tuberculosis.
abstract: 3,4-dihydroxy 2-butanone 4-phosphate synthase (DHBPS) and GTP cyclohydrolase-II (GTPCH-II) are the two initial enzymes involved in riboflavin biosynthesis pathway, which has been shown to be essential for the pathogens. In Mycobacterium tuberculosis (Mtb), the ribA2 gene (Rv1415) encodes for the bi-functional enzyme with DHBPS and GTPCH-II domains at N- and C-termini, respectively. We have determined three crystal structures of Mtb-DHBPS domain in complex with phosphate and glycerol at pH 6.0, with sulphate at pH 4.0 and with zinc and sulphate at pH 4.0 at 1.8, 2.06 and 2.06 Å resolution, respectively. The hydrodynamic volume and enzyme activity studies revealed that the Mtb-DHBPS domain forms a functional homo-dimer between the pH 6.0 and 9.0, however, at pH 5.0 and below, it forms a stable inactive monomer in solution. Furthermore, the functional activity of Mtb-DHBPS and its dimeric state could be restored by increasing the pH between 6.0 and 9.0. The comparison of crystal structures determined at different pH revealed that the overall three-dimensional structure of Mtb-DHBPS monomer remains the same. However, the length of the α6-helix at pH 6.0 has increased from 15 to 22 Å in pH 4.0 by increasing the number of amino acids contributing to the α6-helix from 11 to 15, achieving a higher structural stability at pH 4.0. Taken together our experiments strongly suggest that the Mtb-DHBPS domain can transit between inactive monomer to active dimer depending upon its pH values, both in solution as well in crystal structure.
authors.affiliation: Division of Protein Science and Engineering, Institute of Microbial Technology, Council of Scientific and Industrial Research (CSIR), Sector 39-A, Chandigarh 160036, India.
authors.forename: Mirage
authors.initials: M
authors.lastname: Singh
authors.forename: Pankaj
authors.initials: P
authors.lastname: Kumar
authors.forename: Subramanian
authors.initials: S
authors.lastname: Karthikeyan
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D019751:Intramolecular Transferases / Q000737:chemistry*; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D010446:Peptide Fragments / Q000737:chemistry*; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D010446:Peptide Fragments; D019751:Intramolecular Transferases; C066493:L-3,4-dihydroxy-2-butanone-4-phosphate synthase