The effect of loops on the structural organization of alpha-helical membrane proteins.

ABSTRACT: Loops connecting the transmembrane (TM) alpha-helices in membrane proteins are expected to affect the structural organization of the thereby connected helices and the helical bundles as a whole. This effect, which has been largely ignored previously, is studied here by analyzing the x-ray structures of 41 alpha-helical membrane proteins. First we define the loop flexibility ratio, R, and find that 53% of the loops are stretched, where a stretched loop constrains the distance between the two connected helices. The significance of this constraining effect is supported by experiments carried out with bacteriorhodopsin and rhodopsin, in which cutting or eliminating their (predominately stretched) loops has led to a decrease in protein stability, and for rhodopsin, in most cases, also to the de

SUBMITTER: Tastan O 

PROVIDER: S-EPMC2717299 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature