Cysteine biosynthesis is a potential target for drug development against parasiticLeishmaniaspecies; these protozoa are responsible for a range of serious diseases. To improve understanding of this aspect ofLeishmaniabiology, a crystallographic and biochemical study ofL. majorcysteine synthase has been undertaken, seeking to understand its structure, enzyme activity and modes of inhibition. Active enzyme was purified, assayed and crystallized in an orthorhombic form with a dimer in the asymmetric unit. Diffraction data extending to 1.8 Å resolution were measured and the structure was solved by molecular replacement. A fragment of γ-poly-D-glutamic acid, a constituent of the crystallization mixture, was bound in the enzyme active site. Although a D-glutamate tetrapeptide had insignificant inhibitory activity, the enzyme was competitively inhibited (Ki= 4 µM) by DYVI, a peptide based on the C-terminus of the partner serine acetyltransferase with which the enzyme forms a complex. The structure surprisingly revealed that the cofactor pyridoxal phosphate had been lost during crystallization.
Allosterically Gated Enzyme Dynamics in the Cysteine Synthase Complex Regulate Cysteine Biosynthesis in Arabidopsis thaliana
