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Laminin chain assembly by triple and double stranded coiled-coil structures.
I Hunter1, T Schulthess, J Engel
1Abteilung Biophysikalische Chemie, Biozentrum der Universität, Basel, Switzerland.
The Journal of Biological Chemistry
|March 25, 1992
Summary
Laminin assembly involves the B1-B2 chain forming a coiled-coil intermediate, with the A chain then joining to create a triple coiled-coil molecule. Laminin isoforms lacking the A chain can still form stable structures.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Laminin assembly previously suggested to involve alpha-helical domain interactions of A, B1, and B2 chains.
- Noncoordinate synthesis of laminin chains and absence of the A chain in some cell types prompted further investigation.
Purpose of the Study:
- To examine the molecular mechanism of laminin assembly using isolated laminin A and B1-B2 chains (fragment E8).
- To elucidate the sequential interactions leading to the formation of the triple coiled-coil laminin structure.
Main Methods:
- Isolation and renaturation of laminin fragment E8 chains (E8A and E8B1-B2) from urea.
- Biochemical and ultrastructural analysis of renatured chains and their mixtures.
- Thermal transition analysis to assess molecular stability and structure.
Main Results:
- Isolated E8A showed poor self-association and formed globular structures with minimal alpha-helix.
- E8B1-B2 renatured into stable, rod-like double-stranded coiled coils (30 nm length).
- Mixing E8A and E8B1-B2 in equimolar ratios resulted in molecules indistinguishable from native E8.
Conclusions:
- Laminin assembly likely proceeds via a B1-B2 double coiled-coil intermediate, followed by A chain interaction to form a triple coiled-coil.
- Isoforms composed solely of B1 and B2 chains can form stable, laminin-like structures.