The ANK Repeats of Erythrocyte Ankyrin Form Two Distinct but Cooperative Binding Sites for the Erythrocyte Anion Exchanger (*)
- From the Howard Hughes Medical Institute and Departments of Biochemistry and Cell Biology, Duke University Medical Center, Durham, North Carolina 27710
- §To whom correspondence should be addressed.
Abstract
The 24 ANK repeats of the membrane-binding domain of ankyrin form four folded subdomains of six ANK repeats each. These four
repeat subdomains mediate interactions with at least seven different families of membrane proteins. In the erythrocyte, the
main membrane target of ankyrin is the Cl
/HCO
anion exchanger. This report presents the first evidence that ankyrin contains two separate binding sites for anion exchanger
dimers. One site utilizes repeat subdomain two (repeats 7-12) while the other requires both repeat subdomains three and four
(repeats 13-24). The two sites are positively coupled with a Hill coefficient of 1.4. Since the anion exchanger exists as
a dimer in the membrane, the presence of two binding sites on ankyrin allows ankyrin to interact with four anion exchangers
simultaneously. These findings provide a direct demonstration of the versatility of ANK repeats in protein recognition, and
have important implications for the organization of ankyrin-linked integral membrane proteins in erythrocytes as well as other
cells.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
- Received March 1, 1995.
- Revision received June 19, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
