NOXRED1

Model summary

A soluble human oxidoreductase that uses a Rossmann-like dinucleotide-binding core to catalyze reversible reduction of pyrroline-5-carboxylate to proline in the cytosol. By coupling NAD(H)/NADP(H) chemistry to the proline metabolic node, it helps maintain cellular redox balance and osmoprotective capacity. Its soluble architecture supports dynamic protein associations that tune metabolic responses during calcium-triggered signaling pathways.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The polypeptide contains IPR036291 (NAD(P)-binding domain superfamily, residues 78–185), a Rossmann-like fold that creates a dinucleotide-binding cradle for NAD(H)/NADP(H). Nested within this region is IPR028939 (Pyrroline-5-carboxylate reductase, catalytic, N-terminal domain, residues 78–170), which specifies the enzyme class that reduces the cyclic imine intermediate of the proline pathway. The co-occurrence and overlap of a Rossmann-like NAD(P)-binding core with a P5C-reductase catalytic module establishes a soluble oxidoreductase that uses pyridine nucleotides to interconvert pyrroline-5-carboxylate and proline. This architecture causes two immediate functional consequences: first, a primary molecular role as an NAD(P)-dependent oxidoreductase; second, a propensity for multivalent protein binding that often accompanies soluble dehydrogenase/reductase assemblies.

2. 02

   From this domain logic, I infer molecular function.

   The NAD(P)-binding superfamily (IPR036291) dictates cofactor usage and redox chemistry, while the P5C-reductase catalytic domain (IPR028939) defines substrate scope and reaction directionality. Together they produce a soluble enzyme that binds NAD(H)/NADP(H) and transient protein partners, aligning with GO:0005515 protein binding as a core molecular function. The absence of transmembrane segments or secretion signals further supports a soluble, cytosolic enzyme that forms dynamic complexes.

3. 03

   Connecting function to process, the P5C-reductase chemistry feeds directly into proline metabolism and redox buffering.

   By driving the reversible reduction of pyrroline-5-carboxylate to L-proline, the enzyme modulates cellular responses to energetic and osmotic stress. Calcium-responsive pathways frequently couple cytoskeletal remodeling and metabolic state; a cytosolic redox enzyme that tunes the proline pool can therefore participate in the cellular response to calcium ion (GO:0071277) by adjusting downstream effectors and maintaining redox balance when calcium signaling intensifies.

4. 04

   Cellular location follows from the soluble Rossmann-fold architecture and the lack of targeting signals.

   The enzyme’s physicochemical properties and cytosolic catalytic role point to the cytosol (GO:0005829), consistent with a freely diffusing oxidoreductase that integrates metabolic cues with signaling pathways.

5. 05

   Mechanistically, I hypothesize that the enzyme operates as a cytosolic NAD(P)-dependent reductase that buffers the proline/P5C node.

   By binding NAD(H)/NADP(H) through its Rossmann-like core and engaging substrates via the P5C-reductase catalytic domain, it tunes proline accumulation and redox poise. This positioning predicts transient assemblies with other soluble metabolic enzymes and signaling adaptors. Likely partners include cytosolic proline-pathway enzymes and redox hubs that together coordinate calcium-evoked metabolic responses.