Calorimetric evidence for allosteric subunit interactions associated with inhibitor binding to band 3 transporter

• Published in: The Journal of biological chemistry 1994-01, Vol.269 (1), p.59-61
• Main Authors: VAN DORT, H. M, LOW, P. S, CORDES, K. A, SCHOPFER, L. M, SALHANY, J. M
• Format: Article
• Language: English
• Subjects: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - metabolism; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology; Allosteric Site; Analytical, structural and metabolic biochemistry; Anion Exchange Protein 1, Erythrocyte - antagonists & inhibitors; Anion Exchange Protein 1, Erythrocyte - metabolism; Binding and carrier proteins; Biological and medical sciences; Calorimetry; Fundamental and applied biological sciences. Psychology; Humans; Proteins; Spectrometry, Fluorescence
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(17)42312-X

A calorimetric endotherm occurring at 68 degrees C (the C-transition) has been assigned previously to the integral domain of band 3 and was shown to be shifted to 78 degrees C after covalent binding of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS). In this study, we correlate the fractional appearance of the shifted C-transition with the fraction of DIDS bound to the band 3 monomer population. Our results show a distinctly nonlinear correlation plot with the appearance of the shifted C-transition lagging behind DIDS labeling of the band 3 monomer population. The lag suggests that both monomers of a band 3 dimer must be labeled by DIDS in order for the shifted C-transition to appear at 78 degrees C, implying that the thermal unfolding of the integral domain of band 3 is modulated by allosteric interactions between subunits. This is the first in situ structural evidence supporting ligand-mediated subunit interactions within a "carrier"-type transporter protein oligomer.