NMR exchange broadening arising from specific low affinity protein self- association: analysis of nitrogen-15 nuclear relaxation for rat CD2 domain 1.
Journal of Biomolecular NMR
307 - 320.
Nuclear spin relaxation monitored by heteronuclear NMR provides a useful method to probe the overall and internal molecular motion for biological macromolecules over a variety of time scales. Nitrogen-15 NMR relaxation parameters have been recorded for the N-terminal domain of the rat T-cell antigen CD2 (CD2d1) in a dilution series from 1.20 mM to 40 microM (pH 6.0, 25 degrees C). The data have been analysed within the framework of the model-free formalism of Lipari and Szabo to understand the molecular origin of severely enhanced transverse relaxation rates found for certain residues. These data revealed a strong dependence of the derived molecular correlation time tau c upon the CD2d1 protein concentration. Moreover, a number of amide NH resonances exhibited exchange broadening and chemical shifts both strongly dependent on protein concentration. These amide groups cluster on the major beta-sheet surface of CD2d1 that coincides with a major lattice contact in the X-ray structure of the intact ectodomain of rat CD2. The complete set of relaxation data fit well to an equilibrium monomer-dimer exchange model, yielding estimates of exchange rate constants (kON = 5000 M-1 s-1; kOFF = 7 s-1) and a dissociation constant (KD approximately 3-6 mM) that is consistent with the difficulty in detecting the weak interactions for this molecule by alternative biophysical methods. The self-association of CD2d1 is essentially invariant to changes in buffer composition and ionic strength and the associated relaxation phenomena cannot be explained as a result of neglecting anisotropic rotational diffusion in the analysis. These observations highlight the necessity to consider low affinity protein self-association interactions as a source of residue specific exchange phenomena in NMR spectra of macromolecular biomolecules, before the assignment of more elaborate intramolecular conformational mechanisms
|Title:||NMR exchange broadening arising from specific low affinity protein self- association: analysis of nitrogen-15 nuclear relaxation for rat CD2 domain 1|
|Additional information:||UI - 99455326 LA - Eng RN - 0 (Antigens, CD2) RN - 7727-37-9 (Nitrogen) PT - JOURNAL ARTICLE DA - 19991102 IS - 0925-2738 SB -M CY - NETHERLANDS JC - BJM AA - Author EM - 200001|
|Keywords:||NMR, Proteins, analysis, rat, Antigens, Animal, Antigens, CD2, Biochemistry, chemistry, Dimerization, Methods, Molecular Biology, Nitrogen, Nuclear Magnetic Resonance, rats, Support, Non-U.S.Gov't, X-ray, pH, Structure, ANS|
|UCL classification:||UCL > School of Life and Medical Sciences > Faculty of Life Sciences > Biosciences (Division of)|
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