INTERFACIAL PROPERTIES OF THE POLYHEME CYTOCHROME C(3) SUPERFAMILY FROM DESULFOVIBRIO

In order to compare the interfacial behavior of the polyheme cytochromes c which belong to the cytochrome c(3) superfamily, the monomolecular film technique was used to determine whether and how these metalloproteins interact with (phospho)lipids. Measurements of the variations of surface pressure and surface potential versus time have shown differences in their penetration capacity into phosphatidylcholine, dicaprin, and phosphatidylglycerol films. The Desulfovibrio vulgaris Hildenborough cytochrome with 16 hemes (Hmc) and Desulfovibrio desulfuricans Norway tetra- and octaheme cytochromes c(3), which have been assumed to be soluble periplasmic molecules, may be considered as extrinsic membrane proteins, unlike the D. vulgaris Hildenborough cytochrome c(3) (M(r) 13 000). The interfacial properties are discussed in terms of the available three-dimensional structural data, the electrostatic potential calculation, and the results obtained by hydrophobic cluster analysis of the cytochrome sequences. The very different behavior of the two cytochromes c(3) (M, 13 000) enlightens the role of a particular surface loop in the interaction with a model membrane. A functional interpretation is proposed assuming that the D. vulgaris Hildenborough Hmc and both cytochromes c(3) (M(r) 13 000) and (M(r) 26 000) from the Norway strain might provide the link between periplasmic hydrogen oxidation and cytoplasmic sulfate reduction.