The molecular architecture of mammalian vitreous body collagen fibrils.

Collagen, a fundamental constituent of the extracellular matrix, has long remained elusive to high-resolution structural characterization. Using a tailored system and optimized cryo-electron microscopy processing for long-period filaments, we determined the structure of native collagen fibrils from the porcine vitreous body, with local resolutions extending from 2.6 to 7 angstroms. Each 67-nanometer periodic unit contains type II, V/XI, and IX collagen triple helices together with opticin, at a stoichiometry of 8:4:4:4, which reveals their detailed higher-order molecular packing. Abundant galactose-glucose disaccharides modify hydroxylysine residues in conserved -glycine-X-hydroxylysine- motifs, mediating fibril packing and structural stability. Our structure uncovers the glycan-mediated assembly principle of collagen fibrils and clarifies the structure-function basis of collagens in the vitreous body.