Structural characterisation of native and recombinant forms of the neurotrophic cytokine MK

Abstract

The retinoic acid (RA)-inducible midkine (MK) gene encodes a heparin-binding protein which can induce neutrite outgrowth in cultured mammalian embryonic brain cells. This cytokine shares 65% amino acid sequence identity with another RA-inducible cytokine, pleiotropin (PTN). Both proteins contain 10 conserved cysteine residues, all of which appears to be disulphide linked. MK and PTN are also rich in lysine and arginine residues rendering them susceptible to proteolysis during purification, and making large-scale preparation of these molecules inherently difficult. Recombinant MK has been expressed as a fusion protein using a pGEX vector transfected in E. coli. To enable refolding of MK, the ..