Growing tips of type I collagen fibrils formed in vitro are near-paraboloidal in shape, implying a reciprocal relationship between accretion and diameter.

Abstract

Collagen fibrils generated in vitro at 37C by al. (3, 4). Enzymic removal of C-terminal propeptides from type I pC-collagen (an intermediate in the normal processing of type I procollagen to collagen containing the C-but not the N-terminal propeptides) generates fibrils in vitro under near-physiological conditions. Fibrils formed between 290C and 34TC, large enough to be observable by light microscopy, were found to have a pointed end and a blunt end, with growth occurring only from pointed ends; any growth at a blunt end took the form of a spear-like projection, which then acted as a new pointed tip for oppositely directed growth (5). Quantitative electron-optical measurements on narrower fibrils, formed at 370C and resembling those formed in vivo, are not readily made by conventional procedures. Instead, we have used scanning transmission electron microscopy (STEM) to map the axial distribution of mass along growing tips. The results point to a growth mechanism in which accretion onto a tip surface (rate of mass uptake per unit area) decreases as the local diameter increases.

Collagen fibrillogenesis in situ: Fibril segments undergo post‐depositional modifications resulting in linear and lateral growth during matrix development

“…constructions (Birk et al, 1989b are consistent with the segment-like structures formed in vitro (Holmes et al, 1992;Holmes and Chapman, 1979;Kadler et al, 1987Kadler et al, , 1990Haworth and Chapman, 1977). Individual fibril segments from 14-day chicken embryo dermis and cornea also have been identified (Birk, unpublished data), indicating that the fibril segment is a precursor in the assembly of soft connective tissues during development and growth.…”

Structural Organization of Distinct Domains within the Non-collagenous N-terminal Region of Collagen Type XI

“…However, in patients with Ehlers-Danlos syndrome type VIIB and in animals with dermatosparaxis, diseases where fibrils contain predominantly pN-collagen I molecules, normal diameter fibrils are found. Instead, their surfaces are highly convoluted as surface area is maximized to accommodate these extra propeptide domains (50,51). Thus it is not likely that a steric effect alone is sufficient to explain the effects of retained Npropeptides on fibrillogenesis in these tissues.…”

Influence of fibril taper on the function of collagen to reinforce extracellular matrix

“…Such symmetric tapers are observed in collagen fibrils from ligaments of sea urchin (Eucidaris tribuloides) and sea cucumber (Cucumaria frondosa) (Trotter & Koob 1989;Trotter et al 1998Trotter et al , 2000a. Asymmetric fibrils are observed in vitro (Kadler et al 1990;Holmes et al 1992Fertala et al 1996) and in developing tissues (Birk et al 1995(Birk et al , 1996Graham et al 2000) where one end has a long slender taper (a-tip) and the other a shorter taper (b-tip). However, our model enables us to draw general conclusions about the effects of tapered fibrils which can be applied, separately if need be, to both ends, even if their tapers are not the same.…”

“…Tapered ends are also observed in collagen fibrils formed in vitro (Kadler et al 1990;Holmes et al 1992Fertala et al 1996). Measurements of axial mass distribution along these fibrils using dark-field scanning transmission electron microscopy have established that the taper is paraboloidal in shape (Holmes et al 1992;Trotter et al 1998Trotter et al , 2000aGraham et al 2000).…”