Interaction with stomatin directs human proton channels into cholesterol-dependent membrane domains

Abstract

Many membrane proteins are modulated by cholesterol. Here we report profound effects of cholesterol depletion and restoration on the human voltage-gated proton channel, hHV1, in excised patches but negligible effects in the whole-cell configuration. Despite the presence of a putative cholesterol-binding site, a CARC motif in hHV1, mutation of this motif did not affect cholesterol effects. The murine HV1 lacks a CARC sequence but displays similar cholesterol effects. These results argue against a direct effect of cholesterol on the HV1 protein. However, the data are fully 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. Simultaneous truncation of the large intracellular N and C termini of hHV1 greatly attenuated the cholesterol effect, but C truncation alone did not; this suggests that the N terminus is the region of attachment to lipid domains. Searching for abundant raft-associated proteins led to stomatin. Co-immunoprecipitation experiment results were consistent with hHV1 binding to stomatin. The stomatin-mediated association of HV1 with cholesterol-dependent lipid domains provides a mechanism for cells to direct HV1 to subcellular locations where it is needed, such as the phagosome in leukocytes.