Monitoring the Early Steps of Unfolding of Dicalcium and Mono-Ce3+-Substituted Forms of P43M Calbindin D9k
Early steps of unfolding of P43M Calbindin D9k have been evaluated by NMR spectroscopy on the native dicalcium and on the paramagnetic monocerium-substituted derivative. Although at 2 M GdmHCl the protein core maintains its overall folding and structure, amide 15N R 2 measurements and cross correlat...
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Published in | Biochemistry (Easton) Vol. 42; no. 44; pp. 13066 - 13073 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
11.11.2003
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Subjects | |
Online Access | Get full text |
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Summary: | Early steps of unfolding of P43M Calbindin D9k have been evaluated by NMR spectroscopy on the native dicalcium and on the paramagnetic monocerium-substituted derivative. Although at 2 M GdmHCl the protein core maintains its overall folding and structure, amide 15N R 2 measurements and cross correlation rates between N−H dipole−dipole relaxation and 15N CSA relaxation reveal a closer and stronger packing of the hydrophobic interactions in the protein as a response to the presence of denaturing agents in solution. A complete reorientation of the Met43 side chain toward the hydrophobic core is accomplished by the disappearance of the millisecond dynamics observed on the native form of Calbindin D9k, while cross correlation rates provide evidence that the two-way hydrogen bond between Leu23 and Val61 is broken or substantially weakened. The substitution of the calcium ion in site II with the paramagnetic Ce3+ ion allowed us to obtain a number of long-range nonconventional constraints, namely, pseudocontact shifts, which were used, together with the NOEs collected on the native state, to monitor subtle structural variations occurring in the non-native state of the protein. Although the average rmsd between the structures of native and non-native states is small (0.48 Å), structural rearrangements could be reliably identified. Our results provide unprecedented information about the behavior of Calbindin D9k during the early steps of unfolding. Furthermore, they constitute strong evidence of the efficiency of paramagnetism-based constraints in monitoring subtle structural changes that are beyond the sensitivity of an approach based only on NOE. |
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Bibliography: | This work was supported by European Union Research and Training Network (RTN) Project “Cross correlation between the fluctuations of different interactions: a new avenue for biomolecular NMR” (Contract HPRN-CT-2000-00092) and by RTD Project “Transient NMR” (Contract HPRI-CT-1999−5006). The work has been performed at the EU Large Scale Facility PARABIO (Contract HPRI-CT-1999−00009). B.J. is a fellow of the Marie Curie Training Site NMR in Inorganic Structural Biology (Contract HPMT-2000-000137). B.J. thanks the Generalitat Valenciana for a Ph.D. grant. istex:7D77F65A4D3FBAECC2C2F6FCA646C58AD86E92B8 ark:/67375/TPS-GW50Z8ZR-4 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0006-2960 1520-4995 |
DOI: | 10.1021/bi034638+ |