A model of the platelet factor 4 complex with heparin

Abstract

A model of heparin bound to bovine platelet factor 4 (BPF4) was completed using a graphically designed heparin molecule and the crystallographic coordinates of the native bovine platelet factor 4 tetramer. The oligosaccharides had a chain length of at least eight disaccharide units with the major repeating disaccharide unit consisting of (1----4)-O-(alpha-L-idopyranosyluronic acid 2-sulfate)-(1----4)-(2-deoxy-2-sulfamino-2-D-glucopyranosyl 6-sulfate). Each disaccharide unit carried a -4.0 charge. The structure of BPF4 was solved to 2.6 A resolution with R = 0.237. Each monomer of BPF4 contains an alpha-helix lying across 3 strands of antiparallel beta-sheet. Each helix has four lysines, which have been implicated in heparin binding. These lysine residues are predominantly on one side of the helix and are solvent accessible. Electrostatic calculations performed on the BPF4 tetramer show a ring of strong, positive charge which runs perpendicularly across the helices. Included in this ring of density is His-38, which has been shown by NMR to have a large pKa shift when heparin binds to BPF4. Our model of heparin bound to PF4 has the anionic polysaccharide perpendicular to the alpha-helices, wrapped about the tetramer along the ring of positive charge, and salt linked to all four lysines on the helix of each monomer.

Bovine Lactoferricin Inhibits Basic Fibroblast Growth Factor- and Vascular Endothelial Growth Factor165-Induced Angiogenesis by Competing for Heparin-Like Binding Sites on Endothelial Cells

“…53 Although the exact mechanism by which LfcinB interacts with heparin-like molecules has not yet been elucidated, it is known that LfcinB has a net positive charge of 7.85 at pH 7.0, 54 whereas both heparin and heparan sulfate are negatively charged molecules. 55,56 It was therefore possible that the affinity that LfcinB displayed for heparin-like structures was the result of electrostatic interactions, which would be in line with the recent finding that VEGF 165 interacts with long stretches of anionic residues in heparan sulfate molecules. 57 However, a comparison of the HUVECbinding capacity of native LfcinB and LfcinB with a scrambled amino acid sequence that retained the net positive charge of native LfcinB revealed that the scrambled peptide showed greatly decreased binding to HUVEC monolayers.…”

Characterization of a Neutrophil Cell Surface Glycosaminoglycan That Mediates Binding of Platelet Factor 4

“…This arrangement may help to explain some intriguing observations pertaining to the molecular dimensions of GAG-PF-4 interactions. Although a short heparin fragment of ϳ6/8-mer size is shown to bind PF-4 (16), maximal affinity is attained only for Ͼ20-mers (16,38). These extended sequences are believed to interact with both dimer subunits of a tetramer (38), as has been found for HS (14).…”

“…Although a short heparin fragment of ϳ6/8-mer size is shown to bind PF-4 (16), maximal affinity is attained only for Ͼ20-mers (16,38). These extended sequences are believed to interact with both dimer subunits of a tetramer (38), as has been found for HS (14). The interaction between CS and PF-4 is too weak to show up at the 6/8-mer level, but is clearly evident for ϳ20-mer sequences (Fig.…”

Platelet factor 4 binding to lipid A of Gram-negative bacteria exposes PF4/heparin-like epitopes

“…on May 12, 2018. by guest www.bloodjournal.org From and K66), arginine residues (R20, R22, and R49), histidine residues (H23), and lysine residue (K46). [25][26][27][28][29] Even in the case of amino acid substitutions, one cationic amino acid is often replaced by another positively charged amino acid ( Figure 6). …”