XplA is a cytochrome P450 that was found to mediate the microbial metabolism of the military explosive, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). XplA has an unusual structural organization comprising a heme domain that is fused to its flavodoxin redox partner. XplA, along with its partner reductase XplB, are plasmid encoded and the xplA gene has now been found in divergent genera across the globe with near sequence identity. It has only been detected at explosive-contaminated sites, suggesting rapid dissemination of this novel catabolic activity, possibly within a 50-year period since the introduction of RDX into the environment. XplA belongs to the large cytochrome P450 (P450, CYP) superfamily of heme-containing proteins that catalyze a variety of oxidative reactions of a large number of structurally different endogenous and exogenous compounds in organisms from all major domains of life. CYPs bind their diverse ligands in a buried, hydrophobic active site, which is accessed through a substrate access channel formed by two flexible helices and their connecting loop.