User:Matthew Chien/Sandbox 1: Difference between revisions

C1q is a 460 kDa protein complex composed of six collagen-like stems, each linked to a globular head. This produces a bouquet-like structure shown below. Each collagen-like stem is comprised of three separate chains that form a triple helix structure, totaling 18 polypeptide chains of three different types; A, B, and C. Each chain has an N-terminus in at the CLR and a <scene name='10/1078778/C-termini/1'>C-terminus</scene> at the globular head. Disulfide bonds link the N-terminus ends of A and B chains, with these dimers being linked to the C chains noncovalently. [[Image:Schematic-representation-of-structural-organization-of-human-C1q-and-of-C1-assembly-A.jpeg|thumb|right|520px|N-terminus of C1q]] These form the triple helices that attach to the globular head, making the bouquet-like structure. The globular heads are comprised of three independently folding domains, making them heterotrimeric. The globular heads are very compact and held together by both electrostatic and nonpolar interactions. Each globular head contains a <scene name='10/1078778/Calcium_ion/1'>calcium ion</scene>, responsible for target recognition properties and electrostatic stability. At pH 7.4, the Calcium ion is lost from the globular head, which contributes to IgG binding site recognition. <ref>PMID:23650384</ref><ref>PMID:16245926</ref>