Tilt, twist, and coiling in (beta)-barrel membrane proteins: Relation to infrared dichroism

ABSTRACT The x-ray coordinates of beta-barrel transmembrane proteins from the porins superfamily and relatives are used to calculate the mean tilt of the beta-strands and their mean local twist and coiling angles. The 13 proteins examined correspond to beta-barrels with 8 to 22 strands, and shear numbers ranging from 8 to 24. The results are compared with predictions from the model of Murzin, Lesk, and Chothia for symmetrical regular barrels. Good agreement is found for the mean strand tilt, but the twist angles are smaller than those for open beta-sheets and beta-barrels with shorter strands. The model is reparameterised to account for the reduced twist characteristic of long-stranded …