Kinetics of p-mercuribenzoate binding to sulfhydryl groups on the isolated cytoplasmic fragment of band 3 protein. Effect of hemoglobin binding on the conformation.
Hemoglobin binds to the cytoplasmic domain of band 3 protein (CDB3) at physiologic pH and ionic strength in an oxygen-linked fashion, with deoxyhemoglobin having the higher affinity. The evidence in the literature suggests functional communication between the hemoglobin-binding site on CDB3 and the anion transport sites within the membrane-bound domain of band 3. Since the hemoglobin-binding site is estimated to be over 200 A from the transport domain, the functional communication hypothesis would require the existence of long-range, global changes in the CDB3 dimeric quaternary structure consequent to hemoglobin binding. In this report sulfhydryl reactivity toward p-mercuribenzoate is studied in an attempt to identify such long-range conformational changes. Formation of stoichiometric hemoglobin/CDB3 complexes is shown to produce major changes in sulfhydryl reactivity. Since the sulfhydryl pocket of CDB3 is known to lie at the dimeric interface over 100 A from the hemoglobin-binding site, the observed changes in reactivity suggest that hemoglobin complexation induces a global change in quaternary structure of the CDB3 dimer. This change offers a mechanism to explain functional connections between CDB3-binding sites and the anion transport sites on band 3. The existence of such long-range conformational changes would imply that the CDB3 dimer is poised to function as a cytosolic arm or lever in order to modulate the global structure of the porter.
Salhany
J M
JM
Veterans Administration Medical Center, Omaha, Nebraska.
Cassoly
R
R
D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D008626:Mercuribenzoates / Q000378:metabolism*; D009994:Osmolar Concentration; D011487:Protein Conformation; D013438:Sulfhydryl Compounds / Q000378:metabolism*
C043407:4-mercuribenzoate; D001457:Anion Exchange Protein 1, Erythrocyte; D006454:Hemoglobins; D008626:Mercuribenzoates; D013438:Sulfhydryl Compounds