Nerve growth factor α subunit: Effect of site-directed mutations on catalytic activity and 7S NGF complex formation

Mouse α- and γ-nerve growth factor (NGF) are glandular kallikreins that form a non-covalent complex (7S NGF) with β-NGF. γ-NGF is an active arginine-specific esteropeptidase; the α-subunit is catalytically inactive and has a zymogen-like conformation. Site-directed mutagenesis of α-NGF to alter the N-terminus and three residues in loop 7, a region that contributes to the catalytic center, restored substantial catalytic activity against N-benzoyl arginine-p-nitroanilide as substrate in two derivatives although they were not as active as recombinant γ-NGF. Seven of the 15 derivatives that remained more α-like were able to substitute for native α-NGF in reforming 7S complexes; the other eight derivatives that were more γ-like showed greatly reduced ability to do so. However, the most γ-like α-NGF derivative could not substitute for native γ-NGF in 7S complex formation. These findings suggest that the α-NGF backbone can be corrected to a functional enzyme by the addition of a normal N-terminal structure and two catalytic site substitutions and that the 7S complex requires one kallikrein subunit in the zymogen form and one in an active conformation. Copyright (C) 2000 Elsevier Science B.V.