Estimating the twist of β-strands embedded within a regular parallel β-barrel structure

Abstract

The parallel β-barrel is a recurrent structural motif found in a large variety of different enzymes belonging to the family of α/β-proteins. It has been shown previously that the hyperboloid can be considered as a scaffold describing the parallel β-barrel structure. To assess restraints on β-strand twist imposed by a given scaffold geometry, the notion of scaffold twist, T_s, is introduced. From T_s, the β-strand twist (Tw_β) expected for a given scaffold geometry can be derived and it is verified that this computed twist can be used to identify β-barrels characterized by good hydrogen bonding. It is noted that Tw_β is only slightly affected for β-barrels differing in the number (N) of β-strands, suggesting that restraints on main-chain conformation of β-strands are not likely to account for the N = 8 invariability observed in natural parallel β-barrels thereby strengthening previous work rationalizing this constancy.