| Popis: |
Component C6 is a single-chain plasma glycoprotein of Mr ∼ 108,000 that participates in the last phase of complement activation, namely the formation of the membrane attack complex. This macromolecular assembly consists of C5b through C9 and is a transmembrane pore with a channel diameter of ∼100 A. The polypeptide chain of C6 consists of a single domain of about 250 amino acids referred to as the MACPF along with nine cysteine-rich modules (34–77 amino acids). C6 has two binding sites for C5b; one is reversibly mediated by the C-terminal modules and the other is irreversibly formed by a linker between those modules and the rest of the protein. To C5b6 is added C7, C8 and C9 fashioning a circular complex. The gene for C6 is closely linked to that of C7 on chromosome 5. The importance of C6 for the immune system is demonstrated by rare genetic deficiencies of C6 that render patients susceptible to neisserial infections. |
