MgADP Antagonism to Mg2+-independent ATP Binding of the Sulfonylurea Receptor SUR1

doi:10.1074/jbc.272.37.22983

MgADP Antagonism to Mg²⁺-independent ATP Binding of the Sulfonylurea Receptor SUR1*

From the ^‡Laboratory of Biochemistry, Division of Applied Life Sciences, Kyoto University Graduate School of Agriculture, Kyoto 606-01, Japan and the ^¶Division of Molecular Medicine, Center for Biomedical Science, Chiba University School of Medicine, Chuo-ku, Chiba 260, Japan

Abstract

Pancreatic β-cell ATP-sensitive potassium (K_ATP) channels play an important role in the regulation of glucose-induced insulin secretion. The β-cell K_ATP channel comprises two subunits, the sulfonylurea receptor SUR1, a member of the ATP-binding cassette (ABC) superfamily, and Kir6.2, a member of the inward rectifier K⁺ channel family. The activity of the K_ATP channel is under complex regulation by the intracellular ATP and ADP. To understand the roles of the two nucleotide-binding folds (NBFs) of SUR1 in the regulation of K_ATP channel activity, we introduced point mutations into the core consensus sequence of the Walker A or B motif of each NBF of SUR1 and characterized ATP binding and ADP or MgADP antagonism to it. SUR1 was efficiently photolabeled with 8-azido-[α-³²P]ATP and 8-azido-[γ-³²P]ATP in the presence or absence of Mg²⁺ or vanadate. NBF1 mutations impaired ATP binding, but NBF2 mutations did not. MgADP strongly antagonized ATP binding, and the NBF2 mutation reduced MgADP antagonism. These results show that SUR1, unlike other ABC proteins, strongly binds ATP at NBF1 even in the absence of Mg²⁺ and that MgADP, through binding at NBF2, antagonizes the Mg²⁺-independent high affinity ATP binding at NBF1.

Footnotes

↵* This work was supported by Grant-in-Aid for Scientific Research on Priority Areas of “Channel-Transporter Correlation” 07276101 from the Ministry of Education, Science, and Culture of Japan.The costs of publication of this article were defrayed in part by the payment of page charges. The 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. Tel.: 81-75-753-6106; Fax: 81-75-753-6104; E-mail: uedak{at}kais.kyoto-u.ac.jp.
↵1 The abbreviations used are: SUR, sulfonylurea receptor; ABC, ATP-binding cassette; CFTR, cystic fibrosis transmembrane conductance regulator; Pgp, P-glycoprotein; NBF, nucleotide-binding fold; MRP, multidrug resistance-associated protein; PHHI, persistent hyperinsulinemic hypoglycemia of infancy.
↵2 T. Gonoi, K. Kotake, J. Sanchez, N. Inagaki, and S. Seino, unpublished data.
↵3 Y. Takada, K. Yamada, Y. Taguchi, M. Matsuo, T. Saeki, and K. Ueda, manuscript in preparation.
↵4 K. Yamada, K. Kino, and K. Ueda, manuscript in preparation.
- Received May 27, 1997.
- Revision received June 13, 1997.