Amino acid sequence and characterization of a heparin-binding neurite-promoting factor (p18) from bovine brain

A neurite-promoting factor (p18) was isolated from bovine brain using ammonium sulfate fractionation, sulfated Sephadex G-50 chromatography, heparin-Sepharose gel chromatography, and reverse phase high performance liquid chromatography. The complete amino acid sequence of p18 was determined by automated Edman degradation of S-pyridylethylated p18, and its peptide fragments produced by cyanogen bromide cleavage and by digestion with specific endoproteinases. Alignment of the amino acid sequences of these peptides revealed that p18 consists of 119 amino acid residues with a calculated molecular weight of 14,200. p18 appears to possess five disulfide bonds per molecule. A region of amino acid sequence at the C terminus of p18 shows a structural feature homologous to that around the reactive sites of Kazal-type protease inhibitors. However, p18 did not exhibit anti-trypsin activity. p18 showed very little, if any, mitogenic activity toward NIH 3T3 cells and Swiss mouse 3T3 cells. p18 was found to bind to a specific receptor with an apparent Kd of approximately 8 nM and receptor numbers 1.7 x 10(5) and 1.0 x 10(4) for NIH 3T3 cells and PC12 cells (rat pheochromocytoma cells), respectively.