Modularity of membrane-bound chargetranslocating protein complexes

Energy transduction is the conversion of one form of energy into another; this makes life possible as we know it. Organisms have developed different systems for acquiring energy and storing it in useable forms: The so-called energy currencies. A universal energy currency is the transmembrane difference of electrochemical potential (Δμ). This results from the translocation of charges across a membrane, powered by exergonic reactions. Different reactions may be coupled to charge-translocation and, in the majority of cases, these reactions are catalyzed by modular enzymes that always include a transmembrane subunit. The modular arrangement of these enzymes allows for different catalytic and charge-translocating modules to be combined. Thus, a transmembrane charge-translocating module can be associated with different catalytic subunits to form an energytransducing complex. Likewise, the same catalytic subunit may be combined with a different membrane charge-translocating module. In this work, we analyze the modular arrangement of energy-transducing membrane complexes and discuss their different combinations, focusing on the charge-translocating module.