STRUCTURE OF HYDROLASES - LIPASES AND CELLULASES

Knowledge of lipase mechanisms has increased significantly during the past year. The structural characterization of the opening mechanism of the active site of lipases, as first described for Rhizomucor miehei lipase, has now been extended to the pancreatic lipase-colipase system, and to the Geotrichum candidum/Candida rugosa lipases. In the latter two lipase families, lid opening is far more complicated than for R. miehei lipase. Resolution of the structure of cutinase, an esterase with lipase activity, and determination of the sequence of guinea pig pancreatic lipase showed that these lipases have no lid. The fact that both enzymes are not activated at the interface shows the importance of the lid in the latter phenomenon. On the basis of sequence analysis, cellulases have been divided into different families. Structural determinations of some members of a few of these families confirm that they have different folds. The active sites of these cellulases always seem to contain acidic catalytic groups. The relative spatial position of these groups and their accessibility varies considerably among the cellulases for which structural determinations have been made.