Nereis cuticle collagen: Relationship of fiber ultrastructure to biochemical and biophysical properties

Abstract

The cuticles of annelid worms are composed of many layers of collagenous fibers. The collagens of annelid cuticles have chemical compositions that set them apart from other collagens, have molecular lengths of about 1500 to 1800 nm and are apparently not crosslinked. The distinctive staining pattern that arises from the regular quarter-staggered arrangement of molecules in Type I collagen fibers is not observed in annelid cuticle collagen fibers. To determine the reason for this complete absence of banding, we have examined the cuticle fibers of Nereis virens by X-ray diffraction, light microscopy, and electron microscopy. Novel techniques for making segment-long-spacing crystallites (SLS) from this collagen are described. Our results suggest that the packing arrangement of these unusual molecules is responsible for the lack of banding. The apparently random axial packing arrangement of cuticle collagen molecules results in an absence of regularly spaced gaps between the molecules and in nonaligned charged amino acid clusters. The strength of the cuticle fibers may be derived from the numerous hydrogen bonds and salt bridges that are potentially possible with such extremely long molecules.