Global Structure Changes Associated with Ca2+ Activation of Full-length Human Plasma Gelsolin
Gelsolin regulates the dynamic assembly and disassembly of the actin-based cytoskeleton in non-muscle cells and clears the circulation of filaments released following cell death. Gelsolin is a six-domain (G1-G6) protein activated by calcium via a multi-step process that involves unfolding from a compact form to a more open form in which the three actin-binding sites (on the G1, G2, and G4 subdomains) become exposed. To follow the global structural changes that accompany calcium activation of gelsolin, small-angle x-ray scattering (SAXS) data were collected for full-length human plasma gelsolin at nanomolar to millimolar concentrations of free Ca{sup 2+}. Analysis of these data showed that, upon increasing free Ca{sup 2+} levels, the radius of gyration (R{sub g}) increased nearly 12 {angstrom}, from 31.1 {+-} 0.3 to 43 {+-} 2 {angstrom}, and the maximum linear dimension (D{sub max}) of the gelsolin molecule increased 55 {angstrom}, from 100 to 155{angstrom}. Structural reconstruction of gelsolin from these data provided a striking visual tracking of the gradual Ca{sup 2+}-induced opening of the gelsolin molecule and highlighted the critical role played by the flexible linkers between homologous domains. The tightly packed architecture of calcium-free gelsolin, seen from both SAXS and x-ray crystallographic models, is already partially opened up in as low as 0.5 nM Ca{sup 2+}. Our data confirm that, although the molecule springs open from 0 to 1 {mu} free Ca{sup 2+}, even higher calcium concentrations help to stabilize a more open structure, with increases in R{sub g} and D{sub max} of 2 and 15 {angstrom}, respectively. At these higher calcium levels, the SAXS-based models provide a molecular shape that is compatible with that of the crystal structures solved for Ca{sup 2+}/gelsolin C-terminal and N-terminal halves {+-} monomeric G-actin. Placement of these crystal structures within the boundaries of the SAXS-based model suggests a movement of the G1/G2 subunits that would be required upon binding to actin.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 930001
- Report Number(s):
- BNL-80612-2008-JA; JBCHA3; TRN: US200822%%1154
- Journal Information:
- Journal of Biological Chemistry, Vol. 282, Issue 35; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
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