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Membrane attach complex of complement (MAC): three-dimensional analysis of MAC-phospholipid vesicle recombinants
Journal of Immunology (Baltimore, Md. : 1950)
|May 1, 1982
Summary
The membrane attack complex (MAC) forms a hollow structure that increases vesicle permeability. This study reveals MAC may create protein channels, enhancing membrane permeability beyond lipid reorientation.
Area of Science:
- Structural biology
- Biochemistry
- Immunology
Background:
- The membrane attack complex (MAC) is a key component of the complement system, involved in host defense.
- Understanding MAC's structure and function is crucial for deciphering its role in cellular damage and immune responses.
Purpose of the Study:
- To determine the three-dimensional structure of MAC-vesicle complexes.
- To investigate how MAC interacts with lipid bilayers and affects membrane permeability.
Main Methods:
- Three-dimensional reconstruction from electron micrographs of MAC-vesicle complexes (MAC-DOL and MAC-DML).
- Analysis of negatively stained specimens at various tilting angles under minimal dose conditions.
- Computer-aided reconstruction and densitometric scanning of digitized images.
Main Results:
- MAC forms a hollow structure (16-nm height, 2.0-nm wall thickness) with a torus at its free end.
- Stain penetration into vesicles indicates increased membrane permeability upon MAC binding.
- MAC-vesicle interactions revealed pore formation (up to 2.0-nm or 4.0-nm) and lipid discontinuities, suggesting mechanisms for increased permeability.
Conclusions:
- The MAC structure facilitates increased membrane permeability.
- Protein channel formation by MAC is a potential mechanism for mediating membrane permeability.
- These findings contribute to understanding complement-mediated cell lysis and potential therapeutic targets.