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Fibronectin molecule visualized in electron microscopy: a long, thin, flexible strand
Abstract:
We have determined the structure of plasma fibronectin by electron microscopy of shadowed specimens. the 440,000 molecular weight, dimeric molecule appears to be a long, thin, highly flexible strand. The contour length of the most extended molecules is 160 nm, but a distribution of lengths down to 120 nm was observed, indicating flexibility in extension as well as in bending. The average diameter of the strand is 2 nm and there are no large globular domains. the large fragments produced by limited digestion with plasmin are not globular domains but are segments of the strand, whose length corresponds to the molecular weight of the polypeptide chain. We conclude that each polypeptide chain of the dimeric molecule spans half the length of the strand, with their carboxyl termini joined at the center of the strand and their amino termini at the ends. This model is supported by images of fibronectin-fibrinogen complexes, in which the fibrinogen is always attached to an end of the fibronectin strand.
Insights
Plasma fibronectin, a large dimeric protein, has a long, flexible strand structure. Electron microscopy reveals its molecular architecture, with polypeptide chains extending from the center to the ends.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biology
Background:
- Fibronectin is a crucial extracellular matrix protein involved in cell adhesion and tissue repair.
- Understanding fibronectin's structure is essential for elucidating its biological functions.
Purpose of the Study:
- To determine the three-dimensional structure of plasma fibronectin.
- To elucidate the molecular organization of the fibronectin dimer.
Main Methods:
- Electron microscopy of shadowed specimens.
- Limited proteolysis with plasmin.
- Analysis of fibronectin-fibrinogen complexes.
Main Results:
- Plasma fibronectin (440,000 MW) is a long, thin, flexible strand (160 nm extended length, 2 nm diameter).
- No large globular domains were observed; fragments from plasmin digestion are segments of the strand.
- Fibronectin-fibrinogen complexes show fibrinogen attachment at the fibronectin strand ends.
Conclusions:
- Each polypeptide chain of the fibronectin dimer spans half the strand length.
- Carboxyl termini are joined at the center, and amino termini are at the ends.
- This structural model explains fibronectin's interactions with other molecules.