Interfacial Polar Interactions Affect Gramicidin Channel Kinetics

Abstract

Critical to biological processes such as secretion and transport, protein-lipid interactions within the membrane and at the membrane-water interface still raise many questions. Here we examine the role of lipid headgroups in these interactions by using gramicidin A (gA) channels in planar bilayers as a probe. We show that although headgroup demethylation from phosphatidylcholine (DOPC) to phosphatidylethanolamine decreases the lifetime of gA channels by an order of magnitude in accordance with the currently accepted hydrophobic mismatch mechanism, our findings with diether-DOPC suggest the importance of the headgrouppeptide interactions. According to our x-ray diffraction measurements, this lipid has the same hydrophobic thickness as DOPC but increases gA lifetime by a factor of 2. Thus we demonstrate that peptide-headgroup interactions may dominate over the effect of hydrophobic mismatch in regulating protein function.

Lipid bilayer regulation of membrane protein function: gramicidin channels as molecular force probes

“…This difficulty arises, in part, because d 0 , c 0 , K a and K c are treated as separable parameters in theories of elastic bilayer deformations (Rawicz et al 2000), though they all are determined by the profile of intermolecular interactions across the bilayer (Helfrich 1981;Seddon 1990;Szeiler et al 1990;Petrov 1999). In practice, therefore, these parameters are inter-related: K a and K c are related through scaling relations (Evans 1974); and the bilayer thickness varies with changes in phospholipid head group structure (Nagle & Wiener 1988;Kučerka et al 2005;Rostovtseva et al 2008) or acyl chain unsaturation (Lewis & Engelman 1983;Separovic & Gawrisch 1996), manipulations that are used to alter c 0 . Changes in bilayer composition thus are likely to alter more than one of the parameters that determine DG def .…”

“…A decrease in lipid head group size promotes a more negative c 0 (cf. figure 3c), as well as an increase in bilayer thickness (Nagle & Wiener 1988;Kučerka et al 2005;Rostovtseva et al 2008). Figure 7 shows results from experiments in which c 0 of dioleoylphosphatidylserine/n-decane bilayers was varied by altering the electrostatic repulsion among the charged serine head groups and thus the 'effective' head group size (Lundbaek et al 1997).…”

“…Studies on the bilayer regulation of membrane protein function in systems with defined lipid composition have shown that changes in bilayer properties, such as bilayer thickness or intrinsic lipid curvature, for example, lead to changes in protein function . The interpretation of such experiments is not straightforward, however, because experimental manoeuvres designed to alter a desired bilayer property, such as intrinsic curvature, are likely to alter other bilayer properties also, such as thickness (Rostovtseva et al 2008). That is, though the general principles are well understood, the relative importance of the different contributions to the bilayer deformation energy may be difficult to assess, and it becomes important to have methods to determine the overall energetic consequences of changes in bilayer composition.…”

Membrane Lipid Composition Regulates Tubulin Interaction with Mitochondrial Voltage-dependent Anion Channel

“…Because there is abundant information available on the mechanical properties of DOPC and DOPE membranes and their effect on ion channel functioning (19,32,47,48), we first compared VDAC blockage by tubulin using membranes of a variable DOPC/DOPE composition. The representative single-channel current traces of VDAC reconstituted into planar membranes formed from pure DOPE, DOPC, and a 1:1 mixture of these lipids are shown in Fig.…”

Planar Lipid Bilayers Containing Gramicidin A as a Molecular Sensing System Based on an Integrated Current

“…This difference can be explained by the thickness of a DOPE bilayer, which is larger than that of a DOPC bilayer, owing to a much closer packing of PE molecules. 34 In a DOPC(C18:1)/DSPC(C18:0)/Chol (2:2:1) bilayer, the fraction of channel events with short lifetime significantly increased as compared with the case of a DOPC(C18:1)/Chol bilayer (Fig. S3, Supporting Information), suggesting that the formation of gramicidin A dimer was affected by the presence of unsaturated acyl chains.…”