Biosynthesis of desferrioxamine siderophores initiated by decarboxylases: A functional investigation of two lysine/ornithine-decarboxylases from Gordonia rubripertincta CWB2 and Pimelobacter simplex 3E

Lysine is a precursor for desferrioxamine siderophore biosynthesis. The pathway is often initiated by lysine decarboxylases. However, little is known about those enzymes from Actinobacteria which represents a diverse class of desferrioxamine producers. In this study we focused on the genes grdesA form Gordonia rubripertincta CWB2 and psdesA from Pimelobacter simplex VkMAC-2033D that encode decarboxylases presumed to be involved in the synthesis of desferrioxamine siderophores. The corresponding proteins GrDesA and PsDesA, were heterologously produced in Escherichia coli and purified. PsDesA was isolated bound to the cofactor pyridoxal 5-phosphate and GrDesA was purified in its apo form. PsDesA showed a moderate substrate preference for lysine (K-m = 0.17 mM, k(cat) = 0.26 s(-1)) compared to ornithine (K-m = 0.13 mM, k(cat) = 0.14 s(-1)), while GrDesA exhibited specificity for lysine (K-m = 0.13 mM, k(cat) = 1.2 s(-1)) compared to ornithine (K-m = 2.9 mM, k(cat) = 0.18 s(-1)). The maximum decarboxylase activity of PsDesA was achieved at pH 7.5 at 35 degrees C, although PsDesA was stable up to 40 degrees, its relative activity decreased significantly at 50 degrees C. The temperature optimum (40 degrees C) and thermostability of GrDesA were likewise, but it exhibited maximum activity at pH range 8.0-8.5, and sharply decreased outside of this range. The expression and characterization of these two decarboxylases provides insight into the biosynthetic pathway of desferrioxamines from G. rubripertincta and P. simplex and supports the functional annotation of related pathways.