Defining the domains of type I collagen involved in heparin- binding and endothelial tube formation

Abstract

Cell surface heparan sulfate proteoglycan (HSPG) interactions with type I collagen may be a ubiquitous cell adhesion mechanism. However, the HSPG binding sites on type I collagen are unknown. Previously we mapped heparin binding to the vicinity of the type I collagen N terminus by electron microscopy. The present study has identified type I collagen sequences used for heparin binding and endothelial cell-collagen interactions. Using affinity coelectrophoresis, we found heparin to bind as follows: to type I collagen with high affinity ( Cell surface proteoglycan interactions with type I collagen are likely a ubiquitous mechanism of cell adhesion, yet the interactive sites on these molecules are undefined. Consideration of the complexity of type I collagen structure is relevant to understanding its interactions with heparan sulfate proteoglycans (HSPGs) (see refs. 1 and 2 for review). Type I collagen is secreted as procollagen, which, after proteolytic cleavages, yields the triple-helical monomer composed of two ␣1 and one ␣2 chains. These monomers assemble in a regular staggered fashion into fibrils, which display the repeating D-period pattern, consisting of fine crossfibril bands (called the a, b, c, d, and e bands) in positively stained electron microscopy preparations.Triple-helical type I collagen conformation is necessary for its high-affinity binding to HSPGs, or to heparin, a chemical analog of its heparan sulfate chains (3-5). Furthermore, the C-terminal triple-helical fragment of type I collagen, generated by vertebrate collagenase treatment, showed a higher affinity for heparin than the did the N-terminal fragment (4).To localize more precisely the heparin-binding regions on type I collagen, we studied complexes between collagen monomers and heparin-albumin-gold particles by electron microscopy (6), and we observed heparin binding primarily to a region on the triple helix near the procollagen N terminus. In collagen fibrils, heparin-gold bound to the a bands region within each D-period, which is consistent with an N-terminal heparinbinding site on its monomers. The resolution of the mapping technique was insufficient to assign heparin-binding function to any particular protein sequence. Thus, amino acid sequences were inspected in relation to the heparin-binding locations observed by electron microscopy, searching for basic domains that might be suitable as heparin-binding sites. A highly basic sequence was found near the procollagen N terminus, and within the a bands fibril region, corresponding to amino acid residues 87-92 of the rat ␣1 chain. To test the heparin-binding function of this or other sites of type I collagen, here we have studied how mimetic triple-helical peptides (THPs) including various collagen sequences interact with heparin. We have also explored the function of these sequences in endothelial cell interactions with type I collagen during endothelial tube formation.

Angiogenesis

“…In addition, ECM can exert important signaling functions directly to regulate EC shape and morphogenesis. For example, threedimensional interstitial collagen I stimulates ECs in vitro to assume a spindle-shaped morphology and to align into cords similarly to those observed during angiogenesis in vivo (Delvos et al 1982;Montesano et al 1983;Jackson et al 1994;Richard et al 1998;Sweeney et al 1998;Whelan and Senger 2003). Within collagen I gels, these cords mature to form tubes with hollow lumens through formation and coalescence of intracellular vacuoles (Davis and Camarillo 1996) and expansion of the lumenal compartment through ECM proteolysis (Chun et al 2004;Saunders et al 2006;Stratman et al 2009b).…”

Layer-by-Layer Incorporation of Growth Factors in Decellularized Aortic Heart Valve Leaflets

“…It is also described in literature that collagen contains a high-affinity receptor for heparin explaining the high affinity between heparin and collagen type I. [39][40][41] Interaction between heparin and bFGF can be explained by ionic interaction between both 2-O-sulfate groups and the N-sulfate group of heparin molecules and certain lysine and arginine residues in bFGF. 30 …”

Consortium for osteogenesis imperfecta mutations in the helical domain of type I collagen: regions rich in lethal mutations align with collagen binding sites for integrins and proteoglycans

“…The first of these (helical position 475-493) overlaps with the cross-fibril zone of nonenzymatic glycation [Hadley et al, 1998;Reiser et al, 1992], and falls close to, but does not overlap, a second putative α1β1/α2β1 integrin binding site [Xu et al, 2000]. The second 7-glycine gap (helical position 718-736) overlaps with binding sites for COMP [Rosenberg et al, 1998] and phosphophoryn [Dahl et al, 1998], while the third gap (helical position 79-97) includes one of the major residues for intermolecular collagen cross-linking [Pietz, 1984] and a site for heparin binding in MLBR 1 [San Antonio et al, 1994;Sweeney et al, 1998]. …”

“…MLBR 3 extends from helical residue 920 to the end of the helical region. The gly910-964 stretch of lethal mutations includes one of the two major residues for intermolecular collagen cross-linking (the lysyl residue at helical position 930) [Hanson and Eyre, 1996], as well as sites important for the binding of the decorin proteoglycan core protein , the glycosaminoglycan heparin [San Antonio et al, 1994;Sweeney et al, 1998], and possibly the DDR2 receptor [Schlessinger, 1997;Shrivastava et al, 1997;Vogel et al, 1997]. MLBR 1 is located toward the amino end of the type I collagen helix, where most glycine substitutions are nonlethal.…”