Characterisation of Diaminopimelate Aminotransferase from the novel bacterium Verrucomicrobium Spinosum

Abstract

The intent of this research is to assess the enzyme diaminopimelate aminotransferase (DapL), an enzyme involved in the biosynthetic pathway of the essential amino acid L-lysine. Enzymes involved in L-lysine biosynthesis represent a valuable model for the elucidation of potential therapeutic targets, as animals cannot synthesise L-lysine de novo and require it through the diet. Recently, it has been found that all bacteria in the genus Chlamydia, including Chlamydia trachomatis the causative agent in sexually transmitted infection chlamydia, use the DapL enzyme to syntheise L-lysine. The closest free living relative to C. trachomatis, Verrucomicrobium spinosum is not pathogenic and has the unique feature of exclusively using DapL to synthesise Llysine. V. spinosum is therefore a model organism for assessing the viability of DapL enzymes as therapeutic targets.

In this work, DapL from V. spinosum (VsDapL) was successfully expressed and purified before elucidating any kinetic, structural and biophysical properties of the enzyme. Analysis of the biophysical properties of VsDapL indicates that the enzyme exists in a monomer-dimer equilibrium in solution, however is predominantly dimeric at higher concentrations. This feature has never been reported in DapL orthologues. Finally, the first reported crystal structure for VsDapL using X-ray crystallography is presented and confirms the dimeric structure at higher concentrations found in the biophysical experiments. Comparison of the VsDapL structure with previously characterised DapL orthologues show that it is a typical type I aminotransferase.