Growth of Corynebacterium glutamicum on 5-oxo-L-proline (pyroglutamate) as carbon and nitrogen source requires the PxpR-controlled pxpTABC genes

Abstract

5-Oxo-L-proline (5-OP) is inevitably formed in all cells by spontaneous cyclization of L-glutamate, L-glutamine, or {gamma}-glutamyl phosphate. Its use as a substrate by bacteria has rarely been described. Here, we show that the actinobacterial species Corynebacterium glutamicum can grow well in minimal medium with 5-OP as sole carbon and nitrogen source. We identified the pxpTABC gene cluster as being essential for growth on 5-OP. The pxpT gene encodes a secondary transporter of the APC superfamily which most likely catalyzes 5-OP uptake into the cell. The pxpABC genes encode a recently identified ATP-dependent 5-oxoprolinase that converts 5-OP into L-glutamate for further metabolism. Both PxpT and PxpABC were required for growth with 5-OP. Upstream and divergent to pxpT, the gene pxpR is located, encoding a GntR-type transcriptional regulator. Deletion of pxpR improved growth on 5-OP suggesting that PxpR acts as repressor of the pxpTABC operon. This function was further supported by reporter gene studies. Purified PxpR was shown by isothermal titration calorimetry (ITC) to bind 5-OP with a KD of 726 {+/-} 23 nM. L-proline, L-glutamate, L-glutamine, and L-aspartate were not bound under the conditions tested, suggesting that PxpR is a specific 5-OP biosensor. IMPORTANCEThe utilization of 5-OP as a carbon and nitrogen source for bacteria has rarely been investigated in the past, although this metabolite is ubiquitous in cells due to its non-enzymatic formation from the amino acids L-glutamate and L-glutamine. In Corynebacterium glutamicum cells, but also in other bacteria such as Escherichia coli, L-glutamate is present at concentrations in the range of 100 mM, suggesting a substantial and continuous 5-OP formation. Our results demonstrate that 5-OP can serve both as carbon and nitrogen source for C. glutamicum and presumably also for other bacteria.