CIRCULAR PERMUTANTS IN BETA-GLUCOSIDASES (FAMILY-3) WITHIN A PREDICTED DOUBLE-DOMAIN TOPOLOGY THAT INCLUDES A (BETA ALPHA)(8)-BARREL/

By predicting the general secondary structure for beta-glucosidases (f amily 3), in conjunction with existing knowledge of the circular permu tants present in B. fibrisolvens and R. albus, we were able to find th e canonical elements of the secondary structure. The way these element s are linked suggests that there is a double-domain topology made up o f a (beta/alpha)(8)-barrel domain and a ''mainly all-beta'' domain, A number of already known conserved motifs are located within (or near) the C-terminal part of the putative parallel beta-strands of the (beta /alpha)(8)-barrel, which is consistent with what is known about the lo cation of catalytical sites for enzymes that have this domain topology . Within the circular permutants, two beta/alpha units are located at the N-terminal part of the molecule, whereas the other six beta/alpha units are located at the C-terminal end. In this way, the circular per mutants can be seen to have a putative discontinuous double-domain top ology. (C) 1998 Wiley-Liss,Inc.