Structural characterization of drug targets in bacterial macrocycle production.

摘要

The design and synthesis of novel antibacterial antibiotics has traditionally centered around the modification of macrocyclic targets, including the classes of beta-lactams, macrolides, and aminoglycosides. To better understand the mechanisms by which many bacterial macrocycles are produced, three dimensional structures of targets in the production of different classes of macrocyclic compounds were determined using X-ray protein crystallography. The crystal structure of precorrin-8x methyl mutase (CobH), an enzyme of the aerobic pathway to vitamin B12, provides evidence that the mechanism for methyl migration can plausibly be regarded as an allowed [1,5]-sigmatropic shift of a methyl group from C-11 to C-12 at the C ring of precorrin-8x to afford hydrogenobyrinic acid. The dimeric structure of CobH creates a set of shared active sites that readily discriminate between different tautomers of precorrin-8x and select a discrete tautomer for sigmatropic rearrangement. The active site contains a strictly conserved histidine residue close to the site of methyl migration in ring C of the substrate. Analysis of the structure with bound product suggests that the [1,5]-sigmatropic shift proceeds by protonation of the ring C nitrogen leading to subsequent methyl migration. The crystal structure of the type I holo-acyl carrier protein synthase (AcpS) from Corynebacterium ammoniagenes, in its native form and in complex with coenzyme A, portrays the interactions that both facilitate binding of its natural substrate and enable transfer of 4'-phosphopantetheine (P-pant) onto a variety of acyl carrier domains. The trimeric organization of the AcpS creates binding cavities for coenzyme A and the acyl carrier protein motives at the interfaces between adjacent subunits. The structure of the binary complex also lends considerable evidence for the broad substrate recognition and promiscuity characteristic of other enzymes within the P-pant transferase family.