title: Structure-function analysis of full-length midkine reveals novel residues important for heparin binding and zebrafish embryogenesis.
abstract: Midkine is a heparin-binding di-domain growth factor, implicated in many biological processes as diverse as angiogenesis, neurogenesis and tumorigenesis. Elevated midkine levels reflect poor prognosis for many carcinomas, yet the molecular and cellular mechanisms orchestrating its activity remain unclear. At the present time, the individual structures of isolated half domains of human midkine are known and its functionally active C-terminal half domain remains a popular therapeutic target. In the present study, we determined the structure of full-length zebrafish midkine and show that it interacts with fondaparinux (a synthetic highly sulfated pentasaccharide) and natural heparin through a previously uncharacterized, but highly conserved, hinge region. Mutating six consecutive residues in the conserved hinge to glycine strongly abates heparin binding and midkine embryogenic activity. In contrast with previous in vitro studies, we found that the isolated C-terminal half domain is not active in vivo in embryos. Instead, we have demonstrated that the N-terminal half domain is needed to enhance heparin binding and mediate midkine embryogenic activity surprisingly in both heparin-dependent and -independent manners. Our findings provide new insights into the structural features of full-length midkine relevant for embryogenesis, and unravel additional therapeutic routes targeting the N-terminal half domain and conserved hinge.
authors: Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543.
authors: Jackwee
authors: J
authors: Lim
authors: Sheng
authors: S
authors: Yao
authors: Martin
authors: M
authors: Graf
authors: Christoph
authors: C
authors: Winkler
authors: Daiwen
authors: D
authors: Yang
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D016207:Cytokines / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian; D047108:Embryonic Development / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D029941:Fish Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000077425:Fondaparinux; D009682:Magnetic Resonance Spectroscopy; D000078792:Midkine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D015027:Zebrafish / Q000196:embryology / Q000235:genetics* / Q000378:metabolism
chemical_list: D016207:Cytokines; D029941:Fish Proteins; D011134:Polysaccharides; D011994:Recombinant Proteins; D000078792:Midkine; D000077425:Fondaparinux