Freeze-fracture analysis of the membrane lesion of human complement.
The structure and membrane insertion of the human C5b-9(m) complex, generated by lysis of antibody-coated sheep erythrocytes with whole human serum under conditions where high numbers of classical ring-shaped lesions form, were studied in single and complementary freeze-fracture replicas prepared by unidirectional and rotary shadowing. The intramembrane portion of the C5b-9(m) cylinder was seen on EF-faces as an elevated, circular structure. In nonetched fractures it appeared as a solid stub; in etched fractures a central pit confirmed the existence of a central, water-filled pore in the molecule. Complementary replicas showed that each EF-face ring corresponded to a hole in the lipid plateau of the PF-face. Etched fractures of proteolytically stripped membranes revealed the extramembrane annulus of the C5b-9(m) cylinder on ES-faces and putative internal openings on PS-faces. Allowing for the measured thickness of deposited Pt/C, the dimensions of EF-face rings and ES-face annuli conformed to anticipations derived from negatively stained preparations. Our results support the concept that the hollow cylindrical C5b-9(m) complex penetrates into the inner leaflet of the target erythrocyte membrane bilayer, forming a stable transmembrane protein channel.
D000818:Animals; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins; D004910:Erythrocyte Membrane / Q000648:ultrastructure*; D004912:Erythrocytes / Q000648:ultrastructure*; D005614:Freeze Fracturing; D006801:Humans; D007473:Ion Channels; D008854:Microscopy, Electron; D010447:Peptide Hydrolases / Q000378:metabolism; D012756:Sheep
D015938:Complement Membrane Attack Complex; D007473:Ion Channels; D003165:Complement System Proteins; D010447:Peptide Hydrolases