Most proteins are fixed in the membrane by alpha helices. But some use beta barrels.
Wikipedia describes beta barrels as used for porins, preprotein translocases, and lipocalins. To me, a coiled coil alpha helix structure could surely perform the same functions and given the vast number of proteins using alpha helices there might be some out there.
So my question is twofold:
Are these functions exclusive to beta barrels?
If so, what about alpha helices makes them unsuitable for those functions?