Dipole moment in TIM ⍺/β fold proteins

194-202TIM proteins of ⍺/β barrel fold from ⍺/β class as given in SCOP database were taken for dipole moment analysis. In all, 32 structures were analyzed for their dipole moment contributions. Representative structures from 20 super families in the ⍺/β fold, with different enzyme functions and 12 protein domains of TIM family in TIM super family were considered. The active sites of these proteins are located on the C-terminal side of the β-strands. The molecules of same ⍺/β fold, but differing in their functionality also showed a common electrostatic field pattern along the barrel axis and had the dipole moment along the barrel axis and towards C-terminal end of the b-strands. However, it is observed from our calculations that the dipole moment direction is possibly a consequence of the structural fold, with distribution of charges playing a modulatory role, and does not contribute to the location of active site. We show here that apart from the commonly held view as proposed by Hol et al [Hol W G L, van Duijnen P T and Berendsen H J C (1978) Nature (London), 273, 443-446] of the role of the β helical dipole moment, the β-sheets in the barrel can also have a considerable dipole moment contribution. Taken together with our dipole moment analysis on integral membrane proteins [Vasanthi G and Krishnaswamy S (2002) Indian J Biochem Biophys 39, 93-100], this suggests the need to examine the role of dipole moment in the case of especially β sheets forming barrels