Alkane hydroxylase is a bacterial, integral-membrane di-iron enzyme that shares a requirement for iron and oxygen for activity similar to that of the non-heme integral-membrane acyl coenzyme A (CoA) desaturases and acyl lipid desaturases. The alk genes in Pseudomonas oleovorans encode conversion of alkanes to acyl CoA. The alkane omega-hydroxylase (AlkB) system is responsible for the initial oxidation of inactivated alkanes. It is a three-component system comprising a soluble NADH-rubredoxin reductase (AlkT), a soluble rubredoxin (AlkG), and the integral membrane oxygenase (AlkB). AlkB utilizes the oxygen rebound mechanism to hydroxylate alkanes. This mechanism involves homolytic cleavage of the C-H bond by an electrophilic metal-oxo intermediate to generate a substrate-based radical. As with other members of this superfamily, this domain family has extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. The active site structure of AlkB is not known, however, spectroscopic and genetic evidence points to a nitrogen-rich coordination environment located in the cytoplasm with as many as eight histidines coordinating the two iron ions and a carboxylate residue bridging the two metals. Like all other members of this superfamily, there are eight conserved histidines seen in the histidine cluster motifs: HXXXH, HXXXHH, and HXXHH. These histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within the homolog, stearoyl CoA desaturase. Also included in this CD are terminal alkane hydroxylases (AlkM), xylene monooxygenase hydroxylases (XylM), p-cymene monooxygenase hydroxylases (CymAa), and other related proteins.
Comment:Alkane hydroxylase (AlkB) contains two iron atoms that are ligated to histidine residues; the eight conserved histidines are essential for AlkB activity.
Jiyao W et al.(2023). "The conserved domain database in 2023.",