MUTATIONAL ANALYSIS AND MOLECULAR MODELING OF THE N-TERMINAL KRINGLE-CONTAINING DOMAIN OF HEPATOCYTE GROWTH-FACTOR IDENTIFIES AMINO-ACID SIDE-CHAINS IMPORTANT FOR INTERACTION WITH THE C-MET RECEPTOR

The hepatocyte growth factor receptor (HGFr) transduces a wide range o f biological signals, including mitogenesis, motogenesis and morphogen esis. We recently localized a region within the N-terminal 175 amino a cids of hepatocyte growth factor (HGF), termed HGF/NK1, that is necess ary and sufficient for binding to the HGFr. HGF/NK1 contains an as-yet structurally undefined N-terminal region followed by the first of fou r HGF kringles. We have used a combination of molecular modeling and m utagenesis to dissect the function of this region of HGF. Two mutation -sensitive patches on the proposed surface regions of HGF kringle one (K1) were identified. The first patch consists of residues E159, S161, E195 and R197, all of which are predicted to be close to each other i n the tertiary structure of K1. The second patch, lying on the opposit e side of the kringle, consists of residues D171 and Q173. Mutational analysis of the N-terminal region of HGF identified residue D117 which also appeared to influence receptor binding. We also investigated the properties of a naturally occurring HGF variant (Delta 5-HGF) that ar ises from an alternatively spliced transcript and therefore lacks five residues within K1. Our data suggest that in wild-type HGF, F162 is c rucial in maintaining the hydrophobic core of the kringle. In Delta 5- HGF, the loss of this residue is compensated for by a functional subst itution of F162 with Y167, which is predicted to occupy the Delta 5-HG F K1 core. Comparison of the models of wild-type and Delta 5 kringles reveals that the positions of the presumed receptor binding determinan ts remain unchanged. These studies suggest a structural basis for the receptor binding properties of wild-type and Delta 5-HGF and provide i mportant clues as to the mechanism of kringle-mediated protein - prote in interactions.