Osmolyte effects on the self-association of concanavalin A: testing theoretical models.
The formation and stability of protein-protein interfaces are of obvious biological importance. While a large body of literature exists describing the effect of osmolytes on protein folding, very few studies address the effect of osmolytes on protein association and binding. The plant lectin concanavalin A (ConA), which undergoes a reversible tetramer-to-dimer equilibrium as a function of pH, was used as a model system to investigate the influence of nine osmolytes on protein self-association. The stabilizing or destabilizing impacts of the osmolytes were evaluated from pH titrations combined with circular dichroism spectroscopy. Relative to the dimer, trimethylamine N-oxide, betaine, proline, sarcosine, sorbitol, sucrose, and trehalose all stabilized the ConA tetramer to varying extents. Glycerol had a negligible effect, and urea destabilized the tetramer. From multiple titrations in different osmolyte concentrations, an m-value (a thermodynamic parameter describing the change in the association free energy per molar of osmolyte) was determined for each osmolyte. Experimental m-values were compared with those calculated using two theoretical models. The Tanford transfer model, with transfer free energies determined by Bolen and co-workers, failed to accurately predict the m-values in most cases. A model developed by Record and co-workers, currently applicable only to urea, betaine, and proline, more accurately predicted our experimental m-values, but significant discrepancies remained. Further theoretical work is needed to develop a thermodynamic model to predict the effect of osmolytes on protein-protein interfaces, and further experimental work is needed to determine if there is a general stabilization by osmolytes of such interfaces.
Department of Chemistry, Davidson College , Box 7120, Davidson, North Carolina 28035, United States.
Thomas R
TR
Silvers
Jeffrey K
JK
Myers
D001622:Betaine / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D003208:Concanavalin A / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents / Q000009:adverse effects / Q000737:chemistry / Q000378:metabolism*; D008744:Methylamines / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009994:Osmolar Concentration; D011392:Proline / Q000737:chemistry / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D012521:Sarcosine / Q000737:chemistry / Q000378:metabolism; D064210:Secondary Metabolism; D013012:Sorbitol / Q000737:chemistry / Q000378:metabolism; D013395:Sucrose / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics; D017186:Titrimetry; D014199:Trehalose / Q000737:chemistry / Q000378:metabolism; D014508:Urea / Q000009:adverse effects / Q000737:chemistry / Q000378:metabolism
D007202:Indicators and Reagents; D008744:Methylamines; D003208:Concanavalin A; D001622:Betaine; D013012:Sorbitol; D013395:Sucrose; D014508:Urea; D011392:Proline; D014199:Trehalose; C005855:trimethyloxamine; D012521:Sarcosine