The membrane proton collecting antenna effect studied by Fluorescence Correlation Spectroscopy in a lipid-nanodisc model system – influence of the membrane area and external buffers
(English)Manuscript (preprint) (Other academic)
Lipid membranes can act as proton collecting antennae, thereby significantly accelerating the protonation uptake of proteins responsible for proton transport across biological membranes. This uptake is a crucial step in the energy conversion within all living cells. In this study, we investigated the membrane-size dependence of the proton collecting antenna effect in a lipid nanodisc membrane model system of different sizes, 9nm and 12nm in diameter, with and without incorporation of a proton transporter, cytochrome c oxidase (CytcO). We also investigated how the proton exchange at the membrane-water interface is influenced by buffer molecules in the bulk solution. The proton exchange was monitored via fluorescence fluctuations of individual pH-sensitive fluorophores attached to membranes or to CytcO incorporated into the nanodiscs using fluorescence correlation spectroscopy. Our data confirm the significance of the membrane-water interface for accelerating proton uptake, show that this acceleration depends on the size of the membrane area surrounding the dyes, and indicate that the proton collection antenna can be in operation over a planar membrane-water interface in the range of 10nm in diameter, or possible larger. The buffer dependence for membrane-bound protonatable compounds was found to strongly deviate from the linear dependence, previously observed in both purely three-dimensional and two-dimensional systems. This, more complex, buffer concentration dependence can be explained by considering that also the proton exchange between the membrane surface itself and the bulk is influenced at the different buffer concentrations. Taken together, our findings reveal important biologically relevant aspects for how proton exchange at and across biological membranes are mediated and motivate further studies to better understand how these mechanisms mediate the proton exchange in more complex environments, as experienced in a living cells.
protonation, proton collecting antenna effect, nanodisc, Fluorescence Correlation Spectroscopy (FCS)
Physical Sciences Biophysics
IdentifiersURN: urn:nbn:se:kth:diva-146175OAI: oai:DiVA.org:kth-146175DiVA: diva2:722593
QS 20142014-06-092014-06-092014-06-09Bibliographically approved