A retinoic acid binding cytochrome P450: CYP120A1 from Synechocystis sp. PCC 6803

At least 35 cytochrome P450 (P450, CYP) or cytochrome P450-like genes have been identified in 10 cyanobacterial genomes yet none have been functionally characterized. CYP110 and CYP120 represent the two largest cyanobacterial P450 families with 16 and four members, respectively, identified to date. The Synechocystis sp. PCC 6803 CYP120A1 protein sequence shares high degrees of conservation with CYP120A2 from Trichodesmium erythraeum IMS101 and CYP120B1 and CYP120C1 from Nostoc punctiforme PCC 73102. In this communication, we report the cloning, expression, purification, and characterization of CYP120A1 from Synechocystis. Homology modeling predictions of the three-dimensional structure of CYP120A1 coupled with in silico screening for potential substrates and experimental spectroscopic analyses have identified retinoic acid as a compound binding with high affinity to this P450's catalytic site. These characterizations of Synechocystis CYP120A1 lay the initial foundations for understanding the basic role of cytochrome P450s in cyanobacteria and related organisms.