title: Band 3 catalyzes sickle hemoglobin polymerization.
abstract: We have measured homogeneous and heterogeneous nucleation rates of sickle hemoglobin (HbS) in the presence of a strongly binding deletion mutant of the cytoplasmic domain of band 3 (cdb3), a membrane protein known to form dimers and to bind 2 HbS molecules to such a dimer, and we find that it accelerated both rates by a factor of 2. A weakly binding mutant, in contrast showed no impact on nucleation rates, contrary to naïve expectations of a slight enhancement based on the molecular crowding of the solution by the mutant. We find we can explain these phenomena by a model of HbS-cdb3 interaction in which the strong binding mutant, by stabilizing an HbS dimer, catalyzes the nucleation process, while the weak mutant binds only 1 HbS molecule, effectively inactivating it and thereby compensating for the crowding of the solution by the cdb3. The catalytic behavior we observe could play a role in intracellular processes.
authors.affiliation: Department of Physics, Drexel University, Philadelphia, PA 19104, United States.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Rotter
authors.forename: Haiyan
authors.initials: H
authors.lastname: Chu
authors.forename: Philip S
authors.initials: PS
authors.lastname: Low
authors.forename: Frank A
authors.initials: FA
authors.lastname: Ferrone
mesh_terms: D001457:Anion Exchange Protein 1, Erythrocyte / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D006451:Hemoglobin, Sickle / Q000737:chemistry* / Q000378:metabolism*; D009154:Mutation; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D006451:Hemoglobin, Sickle