In the integrin family, the collagen receptors form a structurally and functionally distinct subgroup. Two members of this
subgroup, α1β1 and α2β1
integrins, are known to bind to monomeric form of type I collagen.
However, in tissues type I collagen monomers are organized
into large fibrils immediately after they are
released from cells. Here, we studied collagen fibril recognition by
By an immunoelectron microscopy method we showed
that integrin α2I domain is able to bind to classical D-banded type I collagen fibrils. However, according to the solid phase binding assay,
the collagen fibril formation appeared to reduce integrin α1I and α2I domain avidity to collagen and to lower the number of putative αI domain binding sites on it. Respectively, cellular α1β1 integrin was able to mediate cell spreading significantly better on monomeric than on fibrillar type I collagen matrix, whereas
α2β1 integrin appeared still to facilitate both cell spreading on fibrillar type I collagen matrix and also the contraction of
fibrillar type I collagen gel. Additionally, α2β1 integrin promoted the integrin-mediated formation of long cellular projections typically induced by fibrillar collagen. Thus,
these findings suggest that α2β1 integrin is a functional cellular receptor for type I collagen fibrils, whereas α1β1 integrin may only effectively bind type I collagen monomers. Furthermore, when the effect of soluble αI domains on type I
collagen fibril formation was tested in vitro,
the observations suggest that integrin type collagen receptors might
guide or even promote pericellular collagen fibrillogenesis.