THE F-O COMPLEX OF THE ATP SYNTHASE OF ESCHERICHIA-COLI CONTAINS A PROTON PATHWAY WITH LARGE PROTON POLARIZABILITY CAUSED BY COLLECTIVE PROTON FLUCTUATION

The F-o complex of the Escherichia coli ATP synthase embedded into car diolipin liposomes was studied by FT-IR spectroscopy. For comparison, respective studies were performed with dried F-o liposomes and with F- o liposomes treated with N,N'-dicyclohexyl-carbodiimide (DCCD), which binds to Asp-61 of subunit c. Furthermore, the effect of H2O-->D2O exc hange on the infrared spectrum was investigated. With F-o liposomes an infrared continuum is observed beginning at about 3000 cm(-1) and ext ending toward smaller wavenumbers. In the DCCD-treated sample, this co ntinuum is no longer observed. It vanishes also with drying of the lip osomes. After H2O-->D2O exchange, this infrared continuum begins at ab out 2350 cm(-1) and is less intense. All of these results demonstrate that a proton pathway in native F-o is present, in which the protons a re shifted in a hydrogen-bonded chain with large proton polarizability due to collective proton tunneling. With the D2O-hydrated system, deu teron polarizability due to collective deuteron motion is observed, bu t the polarizability due to collective deuteron motion is smaller. Suc h pathways are very efficient, because they conduct protons or deutero ns within picoseconds. These pathways lose their polarizability if the F-o complex is blocked by DCCD or if the liposomes are dried. On the basis of our results on the proton polarizability of hydrogen bonds an d hydrogen-bonded systems and on the basis of structural data from the literature, the nature of the proton pathway of the F-o complex of E. coli is discussed.