Surface hydrophobic amino acid residues in cellulase molecules as a structural factor responsible for their high denim-washing performance

The denim-washing performance of six purified fungal cellulases (four endo- 1,4-beta -D-glucanases and two cellobiohydrolases) was compared using a mod el microassay. The performance of cellobiohydrolases per mg of protein was much lower than that of endoglucanases. For endoglucanases, it varied up to 5 times between the best and the worst enzyme. Experiments with amino acid s immobilized on cross-linked agarose showed that their side chains may bin d indigo owing to hydrophobic interactions and formation of hydrogen bonds. The best binding effects provided Tyr and Phe. Analysis of three-dimension al structures of cellulase molecules showed that a certain correlation exis ts between the washing performance of enzyme and (i) quantity (percentage) of aromatic residues exposed to solvent on the surface of protein globule o r (ii) overall percentage of the surface hydrophobic residues. Data present ed provide an evidence that the molecules of certain cellulases, which have hydrophobic domains (clusters of closely located non-polar residues) on th eir surface, may bind indigo and thus act as emulsifiers helping the dye to float out of cellulose fibers to the bulk solution. (C) 2000 Elsevier Scie nce Inc. All rights reserved.