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Molecular and Cellular Biology, November 2005, p. 9189-9197, Vol. 25, No. 21
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.21.9189-9197.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Long-Chain Base Kinase Lcb4 Is Anchored to the Membrane through Its Palmitoylation by Akr1

Akio Kihara, Fumiko Kurotsu, Takamitsu Sano, Soichiro Iwaki, and Yasuyuki Igarashi^*

Department of Biomembrane and Biofunctional Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita 12-jo, Nishi 6-choume, Kita-ku, Sapporo 060-0812, Japan

Received 24 February 2005/ Returned for modification 11 April 2005/ Accepted 5 August 2005

Sphingoid long-chain base kinase Lcb4 catalyzes the production of the bioactive lipid molecules the long-chain base 1-phosphates. Although Lcb4 has no apparent transmembrane-spanning domain, it is tightly associated with the membrane. Here, we demonstrate that Lcb4 is modified by palmitoylation. This modification was greatly reduced in mutants for AKR1, which was recently identified as encoding a protein acyltransferase. In vitro experiments revealed that Akr1 indeed acts as a protein acyltransferase for Lcb4. Studies using site-directed mutagenesis indicated that Cys-43 and Cys-46 are palmitoylated. The loss of palmitoylation on Lcb4 caused several effects, including mislocalization of the protein to the cytosol, reduced phosphorylation, and loss of downregulation during the stationary phase. Although Akr2 is highly homologous to Akr1, the deletion of AKR2 did not result in any remarkable phenotypes. However, overproduction of Akr2 resulted in reduced amounts of Lcb4. We demonstrated that Akr2 is an unstable protein and is degraded in the vacuole. Akr2 exhibits high affinity for Lcb4, and in Akr2-overproducing cells this interaction caused unusual delivery of Lcb4 to the vacuole and degradation.

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* Corresponding author. Mailing address: Department of Biomembrane and Biofunctional Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita 12-jo, Nishi 6-choume, Kita-ku, Sapporo 060-0812, Japan. Phone: 81-11-706-3970. Fax: 81-11-706-4986. E-mail: yigarash{at}pharm.hokudai.ac.jp.

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Molecular and Cellular Biology, November 2005, p. 9189-9197, Vol. 25, No. 21
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.21.9189-9197.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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