Structural basis for different membrane-binding properties of E. coli anaerobic and human mitochondrial 8-oxidation trifunctional enzymes

Facultative anaerobic bacteria such as Escherichia coli have two a282 heterotetrameric trifunctional en-zymes (TFE), catalyzing the last three steps of the 8-oxidation cycle: soluble aerobic TFE (EcTFE) and membrane-associated anaerobic TFE (anEcTFE), closely related to the human mitochondrial TFE (HsTFE). The cryo-EM structure of anEcTFE and crystal structures of anEcTFE-a show that the overall assembly of anEcTFE and HsTFE is similar. However, their membrane-binding properties differ consider-ably. The shorter A5-H7 and H8 regions of anEcTFE-a result in weaker a-8 as well as a-membrane interactions, respectively. The protruding H-H region of anEcTFE-8 is therefore more critical for membrane-association. Mutational studies also show that this region is important for the stability of the anEcTFE-8 dimer and anEcTFE heterotetramer. The fatty acyl tail binding tunnel of the anEcTFE-a hydra-tase domain, as in HsTFE-a, is wider than in EcTFE-a, accommodating longer fatty acyl tails, in good agreement with their respective substrate specificities.