DIMERIZATION OF MIDKINE BY TISSUE TRANSGLUTAMINASE AND ITS FUNCTIONALIMPLICATION

Midkine (MK), a retinoic acid-inducible growth/differentiation factor, serves as a substrate for tissue transglutaminase (Kojima, S., Murama tsu, H., Amanuma, H., and Muramatsu, T. 1995. J. Biol. Chem. 270, 9590 -9596). Upon incubation with transglutaminase MK forms multimers throu gh cross-linkages. Here, we report the following results. 1) Heparin p otentiated the multimer formation by MK. 2) The N- and C-terminal half domains each formed a dimer through the action of transglutaminase. 3 ) Gln(42) or Gln(44) in the N-terminal half and Gln(95) in the C-termi nal half served as amine accepters in the cross-linking reaction, as j udged from the incorporation of putrescine into whole MK or each half domain, and the competitive inhibition of the cross-linking by MK-deri ved peptides containing Gln residue(s). The strongest inhibition was o btained with Ala(41)-Pro(51). 4) This peptide abolished the biological activity of MK to enhance the plasminogen activator activity in bovin e aortic endothelial cells. The inhibition was limited against the MK monomer, and not seen against the MK dimer, separated by gel filtratio n chromatography. These results suggest that dimer formation through t ransglutaminase-mediated cross-linking is an important step as to the biological activity of MK.