Bacterial sodium-coupled proline uptake and fused-PutA catabolism

A reusable bacterial module in which a PutP-family sodium/proline symporter imports L-proline and a fused PutA protein oxidizes it to L-glutamate in two catalytic steps. The FAD-dependent PutA PRODH domain transfers electrons to a quinone while forming P5C, and the NAD-dependent GSALDH domain oxidizes the ring-opened glutamate 5-semialdehyde intermediate to L-glutamate.

The boundary begins with sodium-coupled proline import and ends with L-glutamate. PutA-dependent transcriptional repression, respiratory-chain reactions downstream of quinol, and proline biosynthesis are outside the module. The regulatory role remains part of the PutA gene review; excluding it here keeps this module a connected metabolic pathway rather than implying that the third activity is absent. Full-length PutA orthology is used for both catalytic leaves because PTHR42862:SF1 is dominated by stand-alone aldehyde dehydrogenases and is not a safe selector for the fused architecture. The same PutA molecule therefore appears twice, once for each distinct active site. P5C ring opening to glutamate 5-semialdehyde is nonenzymatic and is represented in the connection between the two PutA reactions rather than as a protein-catalyzed part.