FIGURE 4.

(A) The crystal structure of long-chain alkane monooxygenase (LadA) from Geobacillus thermodenitrificans NG80-2 (Li et al., 2008). The structure is shown in cartoon representation and colored by chain, with the FMN cofactor shown in stick representation and colored cyan. (B) The putative active pocket lined by several residues above the FMN Si-face. H138 possibly acts as a proton donor in the reaction between reduced flavin and oxygen that leads to the formation of the C4a-hydroperoxyflavin intermediate. A hydrophobic cavity formed by M12, A57, V59 and the 4′ OH group of the FMN ribityl chain and the terminal carbon of the alkane chain act to protect the C4a-hydroperoxyflavin from solvent. H17, Y63, Q79, and H311 are believed to be involved in substrate activation and electron transfer during hydroxylation. F10, I18, K347, W348, and F349 should be involved in binding the alkane substrate. LadA amino acids are shown as yellow sticks and labeled; the FMN coenzyme is shown in cyan stick representation. A docked alkane substrate is shown in red stick representation and labeled.