Are most transporters and channels beta barrels?

Publisher Website
Google Scholar
Abstract
Given the sequence of transporters or channels of unknown secondary structure, it is usual to predict their putative transmembrane regions as α-helical. However, recent evidence for a facilitative glucose transporter (GLUT1_ appears inconsistent with such predictions, which has led us to propose an alternative folding model for GLUTs based on the 16-stranded antiparallel β-barrel of porins. Here we apply the same predictive algorithms we used for GLUTs to several other membrane proteins. For some of them, a high-resolution structure has been derived (β-barrels: Rhodobacter capsulatus andEscherichia coli porins; multihelical: colicin A, bacteriorhodopsin, and reaction center L chain); we use them to test the prediction procedures. The other proteins we analyze (GLUT1, CHIP28, acetylcholine receptor alpha subunit, lac permease, Na+-glucose cotransporter, shaker K+ channel, sarcoplasmic reticulum Ca2+-ATPase) are representative of classes of similar membrane proteins. As with GLUTs, we find that the predicted transmembrane segments of these proteins are consistently shorter than expected for transmembrane spanning α-helices, but are of the correct length and number for the proteins to fold instead as porin-like β-barrels.