| Autor: |
Deborah B. Stone, Robert A. Mendelson, Carlos H.I. Ramos, Dieter K. Schneider, Peter A. Timmins, I Krylova, Fernando C. Reinach |
| Rok vydání: |
1998 |
| Předmět: |
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| Zdroj: |
Journal of Molecular Biology. 281:689-704 |
| ISSN: |
0022-2836 |
| DOI: |
10.1006/jmbi.1998.1965 |
| Popis: |
The effects of regulatory amounts of Ca 2+ on the in situ structures of troponin C (TnC) and troponin I (TnI) in whole troponin have been investigated by neutron scattering. In separate difference experiments, 97% deuterated TnC and TnI within whole troponin were studied ±Ca 2+ in 41.6% 2 H 2 O buffers in which protonated subunits were rendered “invisible”. We found that the radius of gyration ( R g ) of TnI decreased by ≈10% upon addition of regulatory Ca 2+ indicating that it was significantly more compact in the presence of Ca 2+ . The apparent cross-sectional radius of gyration ( R c ) of TnI increased by about 9% when regulatory Ca 2+ was bound to TnC. Modeling studies showed that the high- Q scattering patterns of TnI could be fit by a TnI which consisted of two subdomains: one, a highly oblate ellipsoid of revolution containing about 65% of the mass and the other, a highly prolate ellipsoid of revolution consisting of about 35% of the mass. No other fits could be found with this class of models. Best fits were achieved when the axes of revolution of these ellipsoids were steeply inclined with respect to each other. Ca 2+ addition decreased the center of mass separation by about 1.5 nm. The R g of TnI, its high- Q scattering pattern, and the resultant structure were different from previous results on neutron scattering by TnI in the (+Ca 2+ ) TnC·TnI complex. The R g of TnC indicated that it was elongate in situ . The R g of TnC was not sensitive to the Ca 2+ occupancy of its regulatory sites. However, R c increased upon Ca 2+ addition in concert with expectations from NMR and crystallography of isolated TnC. The present observations indicate that TnI acts like a molecular switch which is controlled by smaller Ca 2+ -induced changes in TnC. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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