Redox regulation of 2-carboxy-D-arabinitol 1-phosphate phosphatase in Fabaceae is associated with high Rubisco dark inhibition

Improving Rubisco regulation is an avenue for improving crop output. Minimizing the buildup of Rubisco inhibitors can allow improved catalytic activity and CO2 assimilation. The enzyme 2-carboxy-D-arabinitol 1-phosphate phosphatase (CA1Pase) degrades certain Rubisco inhibitors, yet the mechanisms for its regulation, including the function of its C domain, are not well understood. In this study we analysed Vigna unguiculata (cowpea) CA1Pase in silico and in vitro for structural regions and motifs related to regulation of phosphatase activity. We identified a highly conserved cysteine pair motif tied to redox regulation and potential homodimer formation. Variations in one or both cysteine residues in this motif across species correlate with lower dark inhibitor accumulation levels as compared to related species. The C domain is identified as having a regulatory function and potential evolutionary origins are explored. These insights may inform future efforts toward optimising Rubisco's complex regulatory processes including inhibitor degradation.