HOMOLOGY MODELING OF THE CATALYTIC DOMAIN OF HUMAN FURIN - A MODEL FOR THE EUKARYOTIC SUBTILISIN-LIKE PROPROTEIN CONVERTASES

A model is presented for the three-dimensional structure of the cataly tic domain of the human serine proteinase furin and its interaction wi th model substrates. This homology model is based on the crystal struc tures of subtilisin BPN' and thermitase in complex with the inhibitor eglin, and it also applies to other members of the eukaryotic subtilis in-like proprotein convertases. Predictions are made of the general pr otein fold, inserted loops, disulfide bonds, Ca2+-binding sites and sa lt bridges. A detailed prediction of the substrate-binding region atte mpts to explain the basis of speci ficity for multiple basic residues preceding the cleavage site. Specific acidic residues in the S1, S2 an d S4 subsites of the substrate-binding region of furin are identified which appear to be of particular importance, while residues of the S2' , S3, S5 and S6 subsites may also contribute to substrate binding. Bas ed on this model, protein engineering can be employed not only to test the predicted enzyme-substrate interactions, as demonstrated for huma n furin, but, equally importantly, to design proprotein convertases wi th a desired specificity, or to design novel substrates or inhibitors.