Type IV collagen is a network-forming collagen of the basement membrane, the specialized extracellular matrix underlying an epithelium and supporting other tissue interfaces. Triple-helical molecular units associate into a sheet-like scaffold and are reinforced by intermolecular covalent bonds.[ref]
A Sulfilimine Bond Identified in Collagen IV by Roberto Vanacore and others. 2009, abstract and Fig.3, basement-membrane network architecture
The chemistry of that reinforcement was identified using mass spectrometry and nuclear magnetic resonance. Researchers isolated linked peptides from adjoining units and identified a sulfilimine bond between a methionine residue and a hydroxylysine residue. Chemical reduction broke the linkage and recovered the constituent peptides, supplying a further test of the proposed bond.[ref]
The example connects three scales: the identity of an amino acid side chain, a chemical link between proteins, and stabilization of a supporting tissue network. Knowing only that a specimen contains collagen leaves these structural and chemical distinctions unresolved.
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