The C5 pathway in bacteria is responsible for the synthesis of 5-aminolevulinic acid, which forms the core skeleton of cofactors required for metabolism. One of the key actors in this pathway is a pyridoxamine-5'-phosphate (PMP)/pyridoxal-5'-phosphate (PLP) dependent enzyme called glutamate-1-semialdehyde aminomutase (GSAM). In this study, we crystallized the expression product of the uncharacterized pa4088 gene from the opportunistic pathogen Pseudomonas aeruginosa PA01. The resulting high-resolution structure confirms it to be a member of the GSAM family. Continuous electron density indicates the presence of a PLP cofactor with a Schiff base linkage between the PLP cofactor and the e-amino group of Lys286. A crystal structure of a K286A mutant in complex with PMP is also reported. As GSAM enzymes are not present in mammalian cells, this work provides a starting point for the investigation of GSAM as a target for drug development against P. aeruginosa infection. (C) 2018 Elsevier Inc. All rights reserved.