Characterisation of PigC and HapC, the prodigiosin synthetases from Serratia sp. and Hahella chejuensis with potential for biocatalytic production of anticancer agents

PigC and HapC catalyse the condensation of 4-methoxy-2,2′-bipyrrole-5-carbaldehyde (MBC) with 2-methyl-3-amylpyrrole (MAP) to give the bright red tripyrrolic prodigiosin, which has potent anticancer activity. We have cloned and over-expressed both enzymes and characterised their enzymic activity in vitro using both the natural substrates, MBC and MAP, and analogues of these substrates. Thus a range of prodigiosin analogues have been produced. Both PigC and HapC are membrane-associated enzymes and attempts to fully solubilise them using detergents led to inactivation. The enzymes are ATP-dependent but, unlike the enzymes to which they show the greatest similarity, the by-product is ADP not AMP. Two different slowly interconverting rotamers of prodigiosin exist and the spectral changes with time are consistent with isomerisation of the E,Z (or α) rotamer to the Z,Z (or β) rotameric form.