Refinement of Haemophilus influenzae diaminopimelic acid epimerase (DapF) at 1.75 resolution suggests a mechanism for stereocontrol during catalysis

Diaminopimelate (DAP) epimerase (DapF) is central to the biosynthesis of both lysine and cell-wall peptidoglycan in many bacteria species. The peptidoglycan layer provides great potential for the development of novel antimicrobials as it is a uniquely prokaryotic feature. Crystals of recombinant Haemophilus influenzae DapF that diffract to beyond 2 A resolution have been obtained which facilitated the solution of the structure by molecular replacement at a resolution approximately 1 A higher than that previously determined. An analysis of the structure (i) in comparison to other PLP-independent racemaces and (ii) in relation to the catalytic mechanism and stereospecificity of DapF is presented.