 The molecule is made up of 20 complement control protein (CCP) modules (also referred to as Short Consensus Repeats or sushi domains) connected to one another by short linkers (of between three and eight amino acid residues) and arranged in an extended head to tail fashion.Each of the CCP modules consists of around 60 amino acids with four cysteine residues disulfide bonded in a 1–3 2-4 arrangement, and a hydrophobic core built around an almost invariant tryptophan residue.The CCP modules are numbered from 1–20 (from the N-terminus of the protein); CCPs 1–4 and CCPs 19–20 engage with C3b while CCPs 7 and CCPs 19–20 bind to GAGs and sialic acid.