The structural basis of the catalytic mechanism and regulation of glucose-1-phosphate thymidylyltransferase (RmlA)

The synthesis of deoxy-thymidine di-phosphate (dTDP)-L-rhamnose, an importa nt component of the cell wall of many microorganisms, is a target for thera peutic intervention. The first enzyme in the dTDP-L-rhamnose biosynthetic p athway is glucose-1-phosphate thymidylyltransferase (RmlA). RmlA is inhibit ed by dTDP-L-rhamnose thereby regulating L-rhamnose production in bacteria. The structure of Pseudomonas aeruginosa RmlA has been solved to 1.66 Angst rom resolution. RmlA is a homotetramer, with the monomer consisting of thre e functional subdomains. The sugar binding and dimerization subdomains are unique to RmlA-like enzymes. The sequence of the core subdomain is found no t only in sugar nucleotidyltransferases but also in other nucleotidyltransf erases. The structures of five distinct enzyme substrate-product complexes reveal the enzyme mechanism that involves precise positioning of the nucleo phile and activation of the electrophile. All the key residues are within t he core subdomain, suggesting that the basic mechanism is found in many nuc leotidyltransferases. The dTDP-L-rhamnose complex identifies how the protei n is controlled by its natural inhibitor. This work provides a platform for the design of novel drugs against pathogenic bacteria.