The Journal of Cell Biology, Vol 97, 1686-1692, Copyright © 1983 by The Rockefeller University Press
Solution and surface effects on plasma fibronectin structure
NM Tooney, MW Mosesson, DL Amrani, JF Hainfeld and JS Wall
As assessed by electron microscopy, the reported shape of the plasma
fibronectin molecule ranges from that of a compact particle to an
elongated, rod-like structure. In this study, we evaluated the effects of
solution and surface conditions on fibronectin shape. Freeze-dried,
unstained human plasma fibronectin molecules deposited at pH 7.0-7.4 onto
carbon films and examined by scanning transmission electron microscopy
appeared relatively compact and pleiomorphic, with approximate average
dimensions of 24 nm X 16 nm. Negatively stained molecules also had a
similar shape but revealed greater detail in that we observed irregular,
yarn-like structures. Glutaraldehyde-induced intramolecular cross-linking
did not alter the appearance of plasma fibronectin. Molecules deposited at
pH 2.8, pH 9.3, or after succinylation were less compact than those
deposited at neutral pH. In contrast, fibronectin molecules sprayed onto
mica surfaces at pH 7, rotary shadowed, and examined by transmission
electron microscopy were elongated and nodular with a contour length of
120-130 nm. Sedimentation velocity experiments and electron microscopic
observations indicate that fibronectin unfolds when it is succinylated,
when the ionic strength is raised at pH 7, or when the pH is adjusted to
9.3 or 2.8. Greater unfolding is observed at pH 2.8 at low ionic strength
(less than 0.01) compared with material at that pH in 0.15 M NaCl solution.
We conclude that (a) the shape assumed by the fibronectin molecule can be
strongly affected by solution conditions and by deposition onto certain
surfaces; and that (b) the images of fibronectin seen by scanning
transmission electron microscopy at neutral pH on carbon film are
representative of molecules in physiologic solution.
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