Evidence for a common structure for a class of membrane channels (original) (raw)

Electron microscopic analysis of gap-junction-like structures isolated from an arthropod (Nephrops nowegicus) and composed of a 16-kDa polypeptide, show the functionaI unit to be a star-shaped hexamer of protein arranged around a central channel which runs perpendicular to the plane of the membrane. Estimations of the molecular volume carried out on an averaged projection are consistent with a subunit mass of 16-18 kDa. Fourier transform infrared spectroscopy indicates a high a-helical content for the protein, supporting secondary-structure predictions of four transmembrane a helices/monomer. The averaged projection shows a close resemblance to a hexamer of the 16-kDa protein built on the basis of a four a-helical bundle [Finbow, M