Structural and functional characterization of full-length heparin-binding growth associated molecule

Heparin-binding growth-associated molecule (HB-GAM) was purified from adult bovine brain and chicken heart. The yield of HB-GAM is increased by 5- to 10-fold when 250 mM NaCl is added to the homogenization buffer, indicating that HB-GAM may exist as a complex with an insoluble component of the tissue. The complete amino acid sequence of the brain-derived HB-GAM was established by automated Edman degradation of the intact protein and chemically or enzymatically derived fragments. The mass of bovine HB-GAM as determined by plasma desorption time-of-flight mass spectrometry is 15,291 mass units, which compares favorably with the calculated mass of 15,289 based on the amino acid sequence. Therefore, HB-GAM has not undergone any major post-translational modifications other than cleavage of the signal peptide. These results indicate that previous amino acid sequence analysis of this protein was carried out using truncated HB-GAM. Full-length HB-GAM is not a mitogen for Balb/3T3 clone A31, Balb MK, NRK, or human umbilical vein endothelial cells. HB-GAM does, however, have adhesive properties and neurite extension activity for chick embryo cerebral cortical derived neurons when presented to these cells as a substrate. HB-GAM had little neurite extension activity when presented as a soluble factor.