Electron microscopic analysis of gap‐junction‐like structures isolated from an arthropod (Nephrops norvegicus) and composed of a 16‐kDa polypeptide, show the functional 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 α‐helical content for the protein, supporting secondary‐structure predictions of four transmembrane α helices/monomer. The averaged projection shows a close resemblance to a hexamer of the 16‐kDa protein built on the basis of a four α‐helical bundle [Finbow, M. E., Eliopoulos, E. E., Jackson, P. J., Keen, J. N., Meagher, L., Thompson, P., Jones, P. C. & Findlay, J. B. C. (1992) Protein Eng. 5, 7–15]. The reconstructed image is also similar to that obtained for gap‐junction‐like channels isolated from a related arthropod [Homarus americanus; Sikerwar, S. S., Downing, K. H. & Glaeser, R. M. (1991) J. Struct. Biol. 106, 255–263] whose protein content was unknown but which we demonstrate may be composed of a related 16‐kDa protein. Previous studies have shown a high sequence identity of the Nephrops 16‐kDa protein with the 16‐kDa proteolipid subunit c of the vacuolar H+‐ATPase, both of which in turn bear similarity to the 8‐kDa proteolipid subunit of the F1F0‐ATP synthase. Expression of cDNA coding for the Nephrops 16‐kDa protein in Saccharomyces cerevisiae, in which the endogenous gene coding for the V‐ATPase proteolipid has been inactivated, restores V‐ATPase activity and cell growth.
|Number of pages||10|
|Journal||European Journal of Biochemistry|
|Publication status||Published - Apr 1993|
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