Design of Peptides with High Affinities for Heparin and Endothelial Cell Proteoglycans

Proteoglycan-binding peptides were designed based on consensus sequences in heparin-binding proteins: XBBXBXand XBBBXXBX, where X and B are hydropathic and basic residues, respectively. Initial peptide constructs included (AKKARA)n and (ARKKAAKA)n(n = 1–6). Affinity coelectrophoresis revealed that low Mr peptides (600–1300) had no affinities for low Mr heparin, but higherMr peptides (2000–3500) exhibited significant affinities (Kd ≅ 50–150 nm), which increased with peptide Mr. Affinity was strongest when sequence arrays were contiguous and alanines and arginines occupied hydropathic and basic positions, but inclusion of prolines was disruptive. A peptide including a single consensus sequence of the serglycin proteoglycan core protein bound heparin strongly (Kd ≅ 200 nm), likely owing to dimerization through cysteine-cysteine linkages. Circular dichroism showed that high affinity heparin-binding peptides converted from a charged coil to an α-helix upon heparin addition, whereas weak heparin-binding peptides did not. Higher Mrpeptides exhibited high affinities for total endothelial cell proteoglycans (Kd ≅ 300 nm), and ∼4-fold weaker affinities for their free glycosaminoglycan chains. Thus, peptides including concatamers of heparin-binding consensus sequences may exhibit strong affinities for heparin and proteoglycans. Such peptides may be applicable in promoting cell-substratum adhesion or in the design of drugs targeted to proteoglycan-containing cell surfaces and extracellular matrices.