Heparin-binding neurotrophic factor (HBNF) and MK, members of a new family of homologous, developmentally regulated proteins.

A partial rat cDNA clone coding for a novel neurotrophic factor HBNF was isolated. Nucleotide sequence determination, in combination with the known N-terminal sequence of rat HBNF, allowed deduction of the amino acid sequence of the first 102 residues of mature rat HBNF. HBNF shares high structural homology (55%) with the MK protein (Tomomura et al., J. Biol. Chem. 265, 10765, 1990). Complete alignment of 9 cysteine residues suggests further that the two proteins have similar 3-dimensional structures. HBNF was reported to stimulate neurite outgrowth in neurons and to be expressed in a developmentally regulated manner in the rat brain. MK mRNA was found in retinoid acid-induced teratocarcinoma cells and during early development of the mouse embryo, but no biological activity for MK is yet known. These data suggest that HBNF and MK are members of a novel family of structurally and probably functionally related proteins.