Expression, crystallization and preliminary crystallographic data analysis of PigI, a putative L-prolyl-AMP ligase from the prodigiosin synthetic pathway in Serratia

Prodigiosin, a member of the prodiginines, is a tripyrrole red pigment synthesized by Serratia and some other microbes. A bifurcated biosynthesis pathway of prodigiosin has been proposed in Serratia in which MBC (4‐methoxy‐2,2′‐bipyrrole‐5‐carbaldehyde) and MAP (2‐methyl‐3‐N‐amyl‐pyrrole) are synthesized separately and then condensed by PigC to form prodigiosin. The first step for the synthesis of MBC is the activation of L‐proline by PigI, but its catalytic mechanism has remained elusive. To elucidate its mechanism, recombinant PigI was purified and crystallized. Crystals obtained by the sitting‐drop method belonged to space group P1 and diffracted to 2.0 Å resolution, with unit‐cell parameters a = 51.2, b = 62.8, c = 91.3 Å, α = 105.1, β = 90.1, γ = 92.2°. Matthews coefficient analysis suggested two molecules in the asymmetric unit, with a VM of 2.6 Å3 Da−1 and a solvent content of 52.69%.