CRYSTAL-STRUCTURE OF AN ATP-DEPENDENT CARBOXYLASE, DETHIOBIOTIN SYNTHETASE, AT 1.65-ANGSTROM RESOLUTION

Background: In Escherichia coli, the enzymes of the biotin biosynthesi s pathway are encoded by the bio operon. One of these enzymes, ATP-dep endent dethiobiotin synthetase, catalyzes the carboxylation of 7,8-dia minopelargonic acid leading to the formation of the ureido ring of bio tin. The enzyme belongs to the class of ATP-dependent carboxylases and we present here the first crystal structure determined for this class of enzyme. Results: We have determined the crystal structure of homod imeric dethiobiotin synthetase to 1.65 angstrom resolution. The subuni t consists of a seven-stranded parallel beta-sheet, surrounded by alph a-helices. The sheet contains the classical mononucleotide-binding mot if with a fingerprint peptide Gly-X-X-X-X-X-Gly-Lys-Thr. The mononucle otide binding part of the structure is very similar to the GTP-binding protein H-ras-p21 and thus all GTP-binding proteins. A comparison rev eals that some of the residues, which in H-ras-p21 interact with the n ucleotide and the metal ion, are conserved in the synthetase. Conclusi ons: The three-dimensional structure of dethiobiotin synthetase has re vealed that ATP-dependent carboxylases contain the classical mononucle otide-binding fold. Considerable similarities to the structure of the GTP-binding protein H-ras-p21 were found, indicating that both protein s might have evolved from a common ancestral mononucleotide-binding fo ld.