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J. Biol. Chem., Vol. 279, Issue 4, 2414-2420, January 23, 2004

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Altered Structure and Anion Transport Properties of Band 3 (AE1, SLC4A1) in Human Red Cells Lacking Glycophorin A^*

Lesley J. Bruce, Rui-jun Pan¶, Diane L. Cope||, Makoto Uchikawa**, Robert B. Gunn, Richard J. Cherry¶, and Michael J. A. Tanner

From the Department of Biochemistry, University of Bristol, Bristol BS8 1TD, United Kingdom, the ^¶Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom, the ^||Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom, the ^**Tokyo Blood Center, Japanese Red Cross, Tokyo 150-0012, Japan, and the Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322

We have studied the properties of band 3 in different glycophorin A (GPA)-deficient red cells. These red cells lack either both GPA and glycophorin B (GPB) (M^kM^k cells) or GPA (En(a–) cells) or contain a hybrid of GPA and GPB (MiV cells). Sulfate transport was reduced in all three red cell types to 60% of that in normal control red cells as a result of an increased apparent K_m for sulfate. Transport of the monovalent anions iodide and chloride was also reduced. The reduced iodide transport resulted from a reduction in the V_max for iodide transport. The anion transport site was investigated by measuring iodide fluorescence quenching of eosin-5-maleimide (EMA)-labeled band 3. The GPA-deficient cells had a normal K_d for iodide binding, in agreement with the unchanged K_m found in transport studies. However, the apparent diffusion quenching constant (K_q) was increased, and the fluorescence polarization of band 3-bound EMA decreased in the variant cells, suggesting increased flexibility of the protein in the region of the EMA-binding site. This increased flexibility is probably associated with the decrease in V_max observed for iodide transport. Our results suggest that band 3 in the red cell can take up two different structures: one with high anion transport activity when GPA is present and one with lower anion transport activity when GPA is absent.

Received for publication, September 4, 2003 , and in revised form, November 3, 2003.

^* This work was supported in part by grants from the Wellcome Trust (to M. J. A. T. and R. J. C.) and by National Institutes of Health Grant HL-66173 (to R. B. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Bristol Institute of Transfusion Sciences, Southmead Rd., Bristol BS10 5NB, UK. Tel.: 44-117-991-2126; Fax: 44-117-959-1660; E-mail: lesley.bruce{at}nbs.nhs.uk.

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