Fibrous proteins are elongated, structural macromolecules whose polypeptide chains adopt repetitive conformations and assemble into ordered supramolecular architectures, including fibrils, fibers, microfibrils, and networks. Within glycosylation and glycoprotein research, the term principally encompasses extracellular-matrix proteins that form or organize filamentous assemblies, particularly collagens, elastin-associated proteins, fibrillins, and selected adhesive glycoproteins. Their molecular organization is determined by characteristic sequence motifs, intermolecular associations, covalent cross-links, and post-translational modifications. Collagens contain triple-helical domains composed of repeating Gly–X–Y sequences and assemble into tissue-specific fibrillar or networked structures ^[1]. Elastin is produced from soluble tropoelastin precursors that undergo cross-linking to generate elastic-fiber cores, which associate with microfibrillar glycoproteins ^[2]. Glycosylation of fibrous extracellular proteins includes collagen hydroxylysine O-glycosylation and glycan modifications of associated glycoproteins; these modifications contribute to protein folding, secretion, intermolecular assembly, and matrix architecture ^[3][4].