Amino acid sequence homology between bovine and human platelet proteins

The complete amino acid sequence of bovine platelet factor 4 (PF-4) was determined. Comparison of the 88 residue bovine protein with its 70 residue human counterpart indicated 73% homology. There is 53% homology between this bovine protein and another human platelet protein, beta-thromboglobulin (beta-TG). These heparin binding proteins share greatest homology around a lysine-rich octa-peptide near the carboxy-terminus which is the putative heparin binding domain. Graphic comparison of these proteins suggests that a point mutation at position 55 (human PF-4 numbering) could cause a significant difference among the folding properties of these 3 proteins and might be critical for their different heparin binding properties.