期刊
BIOCHEMISTRY
卷 44, 期 44, 页码 14443-14454出版社
AMER CHEMICAL SOC
DOI: 10.1021/bi050565d
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资金
- NEI NIH HHS [EY06906] Funding Source: Medline
- NHLBI NIH HHS [R01 HL48908] Funding Source: Medline
- NIGMS NIH HHS [R01 GM65399] Funding Source: Medline
The water channel protein PvTIP3;1 (alpha-TIP) is a member of the Major Intrinsic Protein membrane channel family. The in vitro activity of this aquaporin is dependent on phosphorylation, and the protein is phosphorylated in vivo by a membrane-associated Ca2+-dependent kinase. Mutagenesis studies have implicated three serine residues as kinase targets, but only phosphorylation of Ser7 has been observed in vivo. An atomic model of PvTIP3;1 generated by homology modeling suggested that Ser7 is the only residue that would be sterically accessible to kinases. To further explain the phosphorylation of PvTIP3;1, we overexpressed this aquaporin in the methylotrophic yeast Pichia pastoris and purified the hexahistidine-tagged protein by immobilized metal affinity chromatography. Mass spectrometry confirmed that a fraction of recombinant PvTIP3; 1 was phosphorylated. Phosphatase and kinase treatments indicated that Ser7 was the only residue that could be phosphorylated. In addition, mass spectrometry indicated that the native and expressed proteins are N-terminally acetylated. This is the first demonstration that a full-length, recombinant aquaporin can be produced in yeast and authentically phosphorylated in vitro. Characterization of phosphorylation-mediated gating in PvTIP3; I will serve as a paradigm for understanding gating mechanisms of other channels.
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