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Laminin polymerization in vitro. Evidence for a two-step assembly with domain specificity
The Journal of Biological Chemistry
|June 25, 1985
Summary
Laminin, a basement membrane glycoprotein, self-assembles into polymers in vitro. This process is temperature-dependent, reversible, and involves specific interactions at globular domains, suggesting a nucleation-propagation mechanism.
Area of Science:
- Biochemistry
- Cell Biology
- Structural Biology
Background:
- Laminin is a crucial structural glycoprotein in basement membranes.
- Understanding laminin's self-assembly is key to comprehending tissue structure and dynamics.
Purpose of the Study:
- To investigate the in vitro self-association of laminin into polymers.
- To elucidate the mechanism, kinetics, and structural requirements of laminin polymerization.
Main Methods:
- Turbidometry and sedimentation analysis to monitor polymerization.
- Rotary shadowing electron microscopy for structural visualization.
- Limited proteolysis (pepsin digestion) to identify critical domains.
Main Results:
- Laminin self-assembly is temperature-dependent (21-35°C), concentration-dependent, and thermally reversible.
- Polymerization follows a nucleation-propagation mechanism with a critical concentration of ~0.1 mg/ml.
- Self-association occurs specifically at the terminal globular domains, and fragment P1 (lacking these domains) does not self-associate.
- Polymerization involves a divalent cation-independent step followed by a divalent cation-dependent step.
Conclusions:
- Laminin polymerization is a regulated process involving specific molecular interactions.
- The findings provide insights into the structural organization of basement membranes.
- Laminin self-assembly is a multi-step process influenced by temperature, concentration, and divalent cations.