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Published 10 June 2002. doi:10.1083/jcb.200203052
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© The Rockefeller University Press, 0021-9525/2002/6/1017 $5.00
The Journal of Cell Biology, Volume 157, Number 6, June 10, 2002 1017-1028

Article

 Cod1p/Spf1p is a P-type ATPase involved in ER function and Ca2+ homeostasis

Stephen R. Cronin1, Rajini Rao2 and Randolph Y. Hampton1

1 Division of Biology, University of California San Diego, La Jolla, CA 92093
2 Department of Physiology, The Johns Hopkins School of Medicine, Baltimore, MD 21205

Address correspondence to Randolph Y. Hampton, Division of Biology, University of California San Diego, 9500 Gilman Dr. 0347, La Jolla, CA 92093-0347. Tel.: (858) 822-0511. Fax: (858) 534-0555. E-mail: rhampton{at}biomail.ucsd.edu

The internal environment of the ER is regulated to accommodate essential cellular processes, yet our understanding of this regulation remains incomplete. Cod1p/Spf1p belongs to the widely conserved, uncharacterized type V branch of P-type ATPases, a large family of ion pumps. Our previous work suggested Cod1p may function in the ER. Consistent with this hypothesis, we localized Cod1p to the ER membrane. The cod1{Delta} mutant disrupted cellular calcium homeostasis, causing increased transcription of calcium-regulated genes and a synergistic increase in cellular calcium when paired with disruption of the Golgi apparatus–localized Ca2+ pump Pmr1p. Deletion of COD1 also impaired ER function, causing constitutive activation of the unfolded protein response, hypersensitivity to the glycosylation inhibitor tunicamycin, and synthetic lethality with deletion of the unfolded protein response regulator HAC1. Expression of the Drosophila melanogaster homologue of Cod1p complemented the cod1{Delta} mutant. Finally, we demonstrated the ATPase activity of the purified protein. This study provides the first biochemical characterization of a type V P-type ATPase, implicates Cod1p in ER function and ion homeostasis, and indicates that these functions are conserved among Cod1p's metazoan homologues.

Key Words: ion transport; magnesium; protein folding; endoplasmic reticulum; Saccharomyces cerevisiae


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