A novel structural motif and structural trees for proteins containing it

In the present study, a novel structural motif that can be represented as a combination of the known betaalphabeta-unit and psi-motif is described and analyzed. In theory, there are four possible combinations of the motifs since each of them can exist in two forms, left-handed and right-handed. For this study, we have selected 140 nonhomologous proteins in which 158 combinations of such types have been found. The combination of the right-handed psi-motif and the right-handed betaalphabeta-unit has been shown to occur most often (87 cases out of 158) and the combination of the left-handed betaalphabeta-unit and the left-handed psi-motif does not occur at all. Three novel structural trees in which the commonly occurring combinations are taken as the root structures have been constructed.