Human Erythrocyte Membrane Band 3 Protein Influences Hemoglobin Cooperativity

Abstract

Hemoglobin function can be modulated by the red cell membrane but some mechanistic details are incomplete. For example, the 43-kDa chymotryptic fragment of the cytoplasmic portion of red cell membrane Band 3 protein and its corresponding N-terminal 11-residue synthetic peptide lower the oxygen affinity of hemoglobin but effects on cooperativity are unclear. Using highly purified preparations, we also find a lowered Hill coefficient (n values <2) at subequivalent ratios of Band 3 fragment or of synthetic peptide to Hb, resulting in an oxygen affinity that is moderately decreased and a partially hyperbolic shape for the O 2 binding curve. Both normal HbA and sickle HbS display this property. Thus, the determinant responsible for the Hb cooperativity decreases by the 43-kDa fragment resides within its first 11 N-terminal residues. This effect is observed in the absence of chloride and is reversed by its addition. As effector to Hb ratios approach equivalence or with saturating chloride normal cooperativity is restored, and oxygen affinity is further lowered because the shape of the oxygen binding curve becomes completely sigmoidal. The relative efficiencies of 2,3-diphosphoglycerate (DPG), the 43-kDa Band 3 fragment, and the 11-residue synthetic peptide in lowering cooperativity are very similar. The findings are explained based on the stereochemical mechanism of cooperativity because of two populations of T-state hemoglobin tetramers, one with bound effector and the other with free (Perutz, M. F. (1989) Q. Rev. Biophys. 22, 139 -237). As a result of this property, hemoglobin at the membrane inner surface in contact with the N-terminal region of Band 3 could preferentially bind O 2 at low oxygen tension and then release it upon saturation with 2,3-diphosphoglycerate in the interior of the red cell. Membrane modulation of hemoglobin oxygen affinity has particularly interesting implications for the polymerization of hemoglobin S in the sickle red cell.

Critical Role of Two-Dimensional Island-Mediated Growth on the Formation of Semiconductor Heterointerfaces

“…A sigmoidal growth has been reported to occur in biological, geological and chemical processes with cooperative effects [12], wherein the binding of one atom or molecule affects the binding of the subsequent atoms or molecules. The experimental observation of sigmoidal profiles at semiconductor heterointerfaces suggests that similar phenomena occur in materials science.…”

An overview about erythrocyte membrane

“…Therefore it is very important for the flexibility and rigidity of RBC. The N-terminal domain is the site for binding of ankyrin, proteins 4.2 and 4.1, and also glycolytic enzymes (GEs) and haemoglobin [4,8,9,31,35,39,41,52,53,55]. The band 3 C-terminal domain (amino acid 360-911) carries out the anion exchange.…”

“…It is formed by 12-14 TM segments with a short cytoplasmic tail (33 amino acids). Additionally it is responsible for the binding of carbonic anhydrase II [4,8,9,31,35,39,41,51,53,55]. Although band 3 exists in RBC membrane as dimers (70%) it can also be present as tetramers or higher order oligomers (30%) (Fig.…”

“…Erythrocyte cytoskeleton is bound to the erythrocyte membrane through high-affinity protein-protein interactions, [1,3,4,11,17,19,[23][24][25]31,34,35,40,41,50,52,55,56]. The two major membrane protein responsible for the attachment of the cytoskeleton network to the RBC membrane are band 3 and GPC/D (see Fig.…”

Oxidized low-density lipoprotein (Ox-LDL) impacts on erythrocyte viscoelasticity and its molecular mechanism

“…SC contains ankyrin, band 3, and protein 4.2. While band 3 is a multiple transmembranedomain anion exchanger (Zhang et al, 2003), protein 4.2 is tightly membrane-bound, and ankyrin has a b spectrin binding site.…”