The Role in Cell Binding of a β1-bend within the Triple Helical Region in Collagen αl(I) Chain: Structural and Biological Evidence for Conformational Tautomerism on Fiber Surface

Abstract

In its physiological solid state, type I collagen serves as a host for many types of cells. Only the molecules on fiber surface are available for interaction. In this interfacial environment, the conformation of a cell binding domain can be expected to fluctuate between the collagen fold and a distinctive non-collagen molecular marker for recognition and allosteric binding. If the cell binding domain can be localized in contiguous residues within the exposed half of a turn of the triple helix (approximately 15 residues), the need for extensive structural modification and unraveling of the triple helix is avoided. We examined the conformational preferences and biological activity of a synthetic 15-residue peptide (P-15), analogous to the sequence 766GTPGPQGIAGQRGVV780 in the alpha 1 (I) chain. Theoretical studies showed a high potential for a stable beta-bend for the central GIAG sequence. The flanking sequences showed facile transition to extended conformations. Circular dichroism of the synthetic peptide in anisotropic solvents confirmed the presence of beta-strand and beta-bend structures. P-15 inhibited fibroblast binding to collagen in a concentration dependent manner, with near maximal inhibition occurring at a concentration of 7.2 x 10(-6) M. The temporal pattern of cell attachment was altered markedly in the presence of P-15. No inhibition was seen with a peptide P-15(AI), an analogue of P-15 with the central IA residues reversed to AI or with collagen-related peptides (Pro-Pro-Gly)10, (Pro-Hyp-Gly)10, and polyproline, and with several unrelated peptides. Our studies suggest a molecular mechanism for cell binding to collagen fibers based on a conformational transition in collagen molecules on the fiber surface. Since the energy barrier between the collagen fold and beta-strand conformation is low, a local conformational change may be possible in molecules on the fiber surface because of their location in an anisotropic environment. Our observations also suggest that the sequence incorporated in P-15 may be a specific ligand for cells. Unlike other reported cell binding peptides, the residues involved in this interaction are non-polar.

Covalent attachment of P15 peptide to titanium surfaces enhances cell attachment, spreading, and osteogenic gene expression

“…While a number of earlier studies have highlighted the role of P15 to enhance bone formation, relatively few have focused on how it might be utilized to increase implant integration. 10,11,14,26,28,29 Previous studies by Bhatnagar et al, 11 demonstrated enhanced binding of cells to P15-coupled polyglycolate (PGA) fibers and mesh, compared to the PGA alone. Kubler et al, 30 demonstrated cells plated on P15/ABM formed multilayered sheets that clustered around the hydroxyapatite particles in contrast to cells plated on the other substrates which formed only monolayer sheets on the graft particles.…”

“…9 Both collagen and peptides DGEA and P15 are thought to bind integrin receptors stimulating osteoblastic differentiation and expression of the osteogenic phenotype. 10,11 P15 is the common name of a synthetic amino acid peptide (GTPGPQGIAGQRGVV) that is charecterstic of the cell-binding domain of human collagen type I protein. 10 Currently, it is used as a coating on the surface of anorganic bone material (ABM), where it promotes osteoblast differentiation and enhances cell adhesion, migration, and survival.…”

“…10,11 P15 is the common name of a synthetic amino acid peptide (GTPGPQGIAGQRGVV) that is charecterstic of the cell-binding domain of human collagen type I protein. 10 Currently, it is used as a coating on the surface of anorganic bone material (ABM), where it promotes osteoblast differentiation and enhances cell adhesion, migration, and survival. 12 P15/ABM TM (Cerapedics, Westminster, CO) has also been used clinically and shown to improve osteointegration in spinal fusion studies.…”

Augmentation of osseous phenotypes in vivo with a synthetic peptide

“…7 TP508 is a thrombinderived peptide with wide specificity that causes angiogenesis, cytokine release, and appears to act through activation of an inflammatory response. 4,8 P-15 is a collagen-derived high-affinity cell-binding peptide 9 which increases cell attachment and modulates a number of gene products. 10,11 The 73-92 peptide corresponds to residues 73-92 of the knuckle epitope of BMP-2, 7 and while it activates alkaline phosphatase, it also blocks BMP-2 binding to its receptors.…”

Evaluation of ABM/P-15 versus autogenous bone in an ovine lumbar interbody fusion model

“…This product combines P-15, a synthetic 15-amino acid residue with a sequence identical to the cell-binding domain found on the a1(I) chain of Type-I collagen [3], onto an anorganic bovine-derived hydroxyapatite matrix (ABM) through a chemisorptive-coupling procedure [4]. The result is a complex that remains stable under physiologic conditions [5].…”