Identification of heparin-binding sites in midkine and their role in neurite-promotion.
Midkine (MK) is a heparin-binding growth factor, which promotes neurite outgrowth in embryonic neurons and enhances their survival. The three dimensional structure of MK clarified by NMR spectroscopy indicates that several basic amino acids are exposed on the surface of the C-terminal half domain, which retains heparin-binding and neurite-promoting activity. We performed site-directed mutagenesis of these amino acids, and found that mutation of arginine78 reduced the heparin-binding activity. Mutation of either lysine83 or lysine84 scarcely affected heparin-binding activity, while the double mutant involving both lysine residues showed reduction in the activity. Neurite-promoting activity of mutant MKs always correlated with their heparin-binding activity, illustrating the close relationship of the two activities. Thus, the present result verifies the occurrence of two distinct heparin-binding sites involved in neurite-promoting activity of MK molecule.
Asai
T
T
Department of Biochemistry, Nagoya University School of Medicine, Showa-ku, Japan.
Watanabe
K
K
Ichihara-Tanaka
K
K
Kaneda
N
N
Kojima
S
S
Iguchi
A
A
Inagaki
F
F
Muramatsu
T
T
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects*; D016207:Cytokines; D005260:Female; D006493:Heparin / Q000737:chemistry*; D051379:Mice; D000078792:Midkine; D016297:Mutagenesis, Site-Directed; D009414:Nerve Growth Factors / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology; D016501:Neurites / Q000187:drug effects*; D011247:Pregnancy; D051381:Rats
D002352:Carrier Proteins; D016207:Cytokines; D009414:Nerve Growth Factors; D000078792:Midkine; D006493:Heparin