Bilayer Thickness Modulates the Conductance of the BK Channel in Model Membranes

Abstract

The conductance of the BK channel was evaluated in reconstituted bilayers made of POPE/POPS (3.3:1), or POPE/POPS with an added 20% of either SPM (3.3:1:1), CER (3.3:1:1), or CHL (3.3:1:1). The presence of SPM, which is known to increase bilayer thickness, significantly reduced the conductance of the BK channel. To directly test the role of membrane thickness, the conductance of the BK channel was measured in bilayers formed from PCs with acyl chains of increasing length (C14:1-C24:1), all in the absence of SPM. Slope conductance was maximal at a chain length of (C18:1) and much reduced for both thinner (C14:1) and thicker (C24:1) bilayers, indicating that membrane thickness alone can modify slope conductance. Further, in a simplified binary mixture of DOPE/SPM that forms a confined, phase-separated bilayer, the measured conductance of BK channels shows a clear bimodal distribution. In contrast, the addition of CER, which has an acyl chain structure similar to SPM but without its bulky polar head group to POPE/POPS, was without effect, as was the addition of CHL. The surface structure of membranes made from these same lipid mixtures was examined with AFM. Incorporation of both SPM and CER resulted in the formation of microdomains in POPE/POPS monolayers, but only SPM promoted a substantial increase in the amount of the high phase observed for the corresponding bilayers. The addition of CHL to POPE/POPS eliminated the phase separation observed in the POPE/POPS bilayer. The decrease in channel conductance observed with the incorporation of SPM into POPE/POPS membranes was, therefore, attributed to larger SPM-rich domains that appear thicker than the neighboring bilayer.

Acute Alcohol Tolerance Is Intrinsic to the BKCa Protein, but Is Modulated by the Lipid Environment

“…Previous work showed that manipulation of bilayer thickness has profound effects on intrinsic biophysical parameters of BK Ca channel function such as conductance and gating (41,52). Here, we find that bilayer thickness also has powerful effects on the actions of ethanol on BK Ca , changing the sign of action of ethanol from channel potentiation to channel inhibition as the thickness of the bilayer is increased.…”

Identification of Specific Lipid-binding Sites in Integral Membrane Proteins

“…With lipid chain lengths near C 18 often being the most favorable for function (27,28), we employ POPC, POPE, and POPG bilayers that have been extensively used in MD simulations and for which parameter sets are available (29 -31). The bilayer thickness of these bilayers (32) shows good agreement with the calculated hydrophobic thickness of LacY (33), minimizing the effect of hydrophobic mismatch.…”

Mutual adaptation of a membrane protein and its lipid bilayer during conformational changes

“…S2 and Supplementary Note 1). SERCA, however, displays maximum activity when embedded in membranes with hydrophobic , just as seen for many other membrane proteins 14,[25][26][27][28][29] . To inspect the structural basis and possible functional implications of this apparent mismatch, which has also been noted to exist for other membrane proteins 5,30 , we performed MD simulations of SERCA in the E2 and E2P conformations inserted in three pure lipid bilayers ( Supplementary Fig.…”