Human proton channels accumulate in cholesterol dependent membrane domains via direct interaction with stomatin

Abstract

Many membrane proteins are modulated by cholesterol. Here we report strong effects of cholesterol depletion and restoration on the human voltage gated proton channel, hHV1 in excised patches but negligible effects in whole-cell configuration. Despite the presence of a putative cholesterol binding site, a CARC domain in the human voltage gated proton channel, hHV1, mutation of this domain did not affect cholesterol effects. The murine HV1 lacks a CARC sequence but displays similar cholesterol effects. These three results all argue against a direct effect of cholesterol on HV1. We propose that the data are explainable if HV1 preferentially associates with cholesterol-dependent lipid domains, or “rafts.” The rafts would be expected to concentrate in the membrane/glass interface and to be depleted from the electrically-accessible patch membrane. This idea is supported by evidence that HV1 channels can diffuse between seal and patch membranes when suction is applied. Suction pulls membrane constituents including HV1 into the patch. In whole-cell studies moderate osmotic stretch does not noticeably alter H+currents. Simultaneous truncation of the large intracellular N- and C-termini greatly attenuated the cholesterol effect, but C-truncation only did not. We conclude that the N-terminus is the region of attachment to lipid domains. Searching for abundant raft-associated molecules led to stomatin. Co-immunoprecipitation experiments showed that hHV1 binds to stomatin. The stomatin-mediated association of HV1 with cholesterol-dependent lipid domains provides a mechanism for cells to direct HV1 to subcellular location where it is needed, such as the phagosome in leukocytes.SignificanceMany membrane proteins are modulated by cholesterol. Here we explore effects of cholesterol on the human voltage-gated proton channel, hHV1. Although we find little evidence for a direct effect, cholesterol was found to exert a strong influence over H+current in excised membrane patches. These effects are explainable by hypothesizing that HV1 preferentially associates with cholesterol-dependent membrane lipid domains. We postulate that HV1 diffuses within the membrane and is concentrated in such domains that are anchored to the pipette glass by large membrane proteins. We find that HV1 co-immunoprecipitates with stomatin, a typical component of cholesterol dependent lipid domains. The association of HV1 with lipid domains provides a mechanism for directing HV1 to specific subcellular locations to perform specific functions.