Ecto-ATPase Activity of α-Sarcoglycan (Adhalin)*
- Romeo Betto‡§,
- Luigi Senter¶,
- Stefania Ceoldo¶,
- Elena Tarricone¶,
- Donatella Biral‡ and
- Giovanni Salviati†‡¶
- From the ‡Consiglio Nazionale delle Ricerche Unit for Muscle Biology and Physiopathology and the ¶Department of Biomedical Sciences, University of Padova Medical School, Viale Giuseppe Colombo 3, I-35121 Padova, Italy
Abstract
α-Sarcoglycan is a component of the sarcoglycan complex of dystrophin-associated proteins. Mutations of any of the sarcoglycan genes cause specific forms of muscular dystrophies, collectively termed sarcoglycanopathies. Importantly, a deficiency of any specific sarcoglycan affects the expression of the others. Thus, it appears that the lack of sarcoglycans deprives the muscle cell of an essential, yet unknown function. In the present study, we provide evidence for an ecto-ATPase activity of α-sarcoglycan. α-Sarcoglycan binds ATP in a Mg2+-dependent and Ca2+-independent manner. The binding is inhibited by 3′-O-(4-benzoyl)benzoyl ATP and ADP. Sequence analysis reveals the existence of a consensus site for nucleotide binding in the extracellular domain of the protein. An antibody against this sequence inhibits the binding of ATP. A dystrophin·dystrophin-associated protein preparation demonstrates a Mg-ATPase activity that is inhibited by the antibody but not by inhibitors of endo-ATPases. In addition, we demonstrate the presence in the sarcolemmal membrane of a P2X-type purinergic receptor. These data suggest that α-sarcoglycan may modulate the activity of P2X receptors by buffering the extracellular ATP concentration. The absence of α-sarcoglycan in sarcoglycanopathies leaves elevated the concentration of extracellular ATP and the persistent activation of P2X receptors, leading to intracellular Ca2+ overload and muscle fiber death.
Footnotes
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↵* This work was supported by institutional funds from the Consiglio Nazionale delle Ricerche and by Grant 692 from the Fondazione Telethon of Italy (to G. S. and R. B.).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.
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↵† Deceased March 12, 1998.
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↵§ To whom correspondence should be addressed. Tel.: 39-49-8276027; Fax.: 39-49-8276040; E-mail:betto{at}civ.bio.unipd.it.
- Abbreviations:
- DAPs
-
dystrophin-associated proteins
- DMD
-
Duchenne muscular dystrophy
- LGMD
-
limb girdle muscular dystrophy
- BzATP
-
3′-O-(4-benzoyl)benzoyl ATP
- DTT
-
dithiothreitol
- PAGE
-
polyacrylamide gel electrophoresis
- NOS
-
nitric oxide synthase
- nNOS
-
neuronal-type nitric oxide synthase
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- Received November 16, 1998.
- Revision received December 18, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
