Amino acid sequence of human platelet factor 4.

Abstract

Human platelet factor 4, a protein that binds heparin, has been purified to apparent homogeneity and the complete amino acid sequence of the protein has been determined. The 70-residue polypeptide chain contains no methionine, tryptophan, or phenylalanine, and contains only a single tyrosyl residue. The sequence analysis demonstrates a highly negatively charged amino-terminal region. The carboxyl-terminal region of the polypeptide is unusual in that it contains a repetitive clustering of positively charged and hydrophobic pairs of amino acids; preliminary evidence suggests that this domain may play a role in the binding of heparin.Heparin is a potent anticoagulant that is used extensively in clinical medicine for the treatment of thrombotic disease (1). Platelets release-a small protein that neutralizes the anticoagulant effect of heparin (2). A plasma factor with this property was first predicted inr 1948 by Conley (3) when he noticed that patients with thrombocytopenia had increased sensitivity to heparin. Partial purification of the specific, platelet-derived protein, referred to as platelet factor 4 (4), was reported by Deutsch et al. (5), and, more recently, various investigators have published methods for isolation of the protein in an apparently homogeneous form (6-13). Platelet factor 4 is a relatively small, heat-stable protein that is insoluble in solutions of low ionic strength, but that is soluble in high ionic strength solutions and in acidic buffers (12, 13). Platelet factor 4 is released with and bound to a carrier proteoglycan molecule from which it is displaced by heparin (8, 10).Because of a possible relationship of platelet factor 4 to arterial and venous thrombosis (14)(15)(16)(17)(18)(19)(20) tained by precipitation between ammonium sulfate concentrations of 50 and 100%, by affinity chromatography on columns of heparin-E-aminocaproic acid-Sepharose prepared as described by Schmer (21), and by gel filtration through Sephadex G-100 in 1 M NaCl. These methods and the modified thrombin time used in the assay of platelet factor 4 were adapted from those reported by Levine and Wohl (12). Purified platelet factor 4 binds 27 units of heparin per mg of protein.The purified protein appears as a single band after polyacrylamide gel electrophoresis (15% acrylamide) in the presence of sodium dodecyl sulfate and is estimated to be at least 95% pure both by this criterion and by automated Edman degradation of the intact S-carboxamidomethylated protein. The purity of the preparation was also established by immunological techniques. The IgG fraction of antisera obtained from rabbits immunized with platelet factor 4 was isolated by ammonium sulfate precipitation and DEAE-cellulose chromatography (22). The purified IgG gave a single precipitin line against purified platelet factor 4 in immunodiffusion experiments, suggesting that the purified protein behaves as a single major antigenic species.

Manipulation of hydrogel assembly and growth factor delivery via the use of peptide–polysaccharide interactions

“…Specifically, the PF4 ZIP peptide was synthesized and attached to the termini of vinyl-sulfone modified star PEG. The PF4 ZIP peptide, a GCN4-based coiled-coil motif designed to mimic the lysine-rich heparinbinding region of PF4 [34,58], was employed in these studies, with ultimate goals of expanding the number and types of binding interactions employed in hydrogel assembly and to manipulate materials properties and delivery profiles. The use of PF4 ZIP was motivated by the fact that platelet factor 4 (PF4) is perhaps the strongest heparin-binding protein known [59].…”

A recipe for designing water‐soluble, β‐sheet‐forming peptides

“…&Sheet amino acid sequence alignments. The amino acid sequences are shown for the P-sheet domains of PF4 (Deuel et al, 1977;Holt & Niewiarowski, 1985), IL-8 (Schmid & Weissmann, 1987), Gro-a (Anisowicz et al, 1987), and designed peptides ppep-1, ppep-2, ppep-3, and ppep-4. &Sheet residues are blocked-in and lines connect residues that are paired between strands.…”

The COOH-Terminal Peptide of Platelet Factor-4 Variant (CXCL4L1/PF-4var47-70) Strongly Inhibits Angiogenesis and Suppresses B16 Melanoma Growth In vivo

“…Platelet factor-4 (CXCL4/PF-4) has been identified as a tetrameric heparin-binding protein released from the α-granules of activated platelets long before the term chemokine was introduced (1). Later, small chemotactic cytokines, which are essential mediators in leukocyte migration to inflammatory sites and to secondary lymphoid organs, were identified and named chemokines (2).…”