FIG. 1.

Topology model of the P. putida GPo1 AH. The TM helices are represented by straight cylinders and numbered 1 through 6, and the connecting peptides are indicated by lines between the cylinders (not to scale). The N- and C-terminal ends of the protein are located in the cytoplasm, and the TM helices are connected by three short peptides on the periplasmic side of the membrane. About 60 to 65% of AlkB is located in the cytoplasm (34). (A) Wild-type enzyme (W55) binding dodecane; (B) W55S mutant enzyme binding hexadecane. The open circles denote the approximate locations of the four conserved histidine-containing sequence motifs (motif A, H₁₃₈EXXHK₁₄₃; motif B, E₁₆₇HXXGHH₁₇₃; motif C, N₂₆₉YXEHYG₂₇₅; and motif D, L₃₀₉QRHXDHHA₃₁₇), two of which (motifs A and C) are located at the ends of TM helices 4 and 6, close to the surface of the cytoplasmic membrane. Filled circles denote the approximate locations of the two iron atoms liganded by the conserved histidine-containing sequence motifs.