= Collagen IV NC1 domain
{c}
The <Collagen IV NC1 domain> is the noncollagenous <protein domain> at the <C-terminus> of a <Collagen IV> chain. NC1 regions participate in the end-to-end assembly of the network that supports a <basement membrane>. A three-chain <Collagen IV protomer> presents three NC1 regions at this end; association of two such ends forms a six-subunit <Collagen IV NC1 hexamer>.<A Sulfilimine Bond Identified in Collagen IV by Roberto Vanacore and others>[Introduction and Figure 3; trimeric NC1 ends of adjoining protomers and hexamer organization]{ref}
The counting is useful: a six-subunit junction joins two three-chain molecular units, rather than requiring each <Collagen IV> molecule to contain six chains. The <Collagen IV NC1 hexamer> describes a local meeting point in the larger scaffold.
The junction is reinforced by <sulfilimine bonds> between <methionine> and <hydroxylysine> residues of adjoining units. In 2009, <mass spectrometry> and <nuclear magnetic resonance> measurements on isolated linked <peptides> identified this bond. Chemical reduction separated the linked <peptides>, providing another test of the proposed structure. Up to six such links can reinforce the interface between the two NC1 ends.<A Sulfilimine Bond Identified in Collagen IV by Roberto Vanacore and others>[Table 1 and Figures 1–3; mass/NMR identification, reductive cleavage and placement of up to six crosslinks]{ref}
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