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Multiple phosphorylations in the C-terminal tail of plant plasma membrane aquaporins: role in subcellular trafficking of AtPIP2;1 in response to salt stress.
Mol Cell Proteomics. 2008 Jun; 7(6):1019-30
Michael Gjedde Palmgren, University of Copenhagen, Denmark. F1000 Structural Biology
06 Aug 2008 | New Finding
This is an interesting paper in that is shows that phosphorylation at specific sites in a plasma membrane protein is required for its surface delivery. The authors have used mass spectrometry to identify two sites in the C-terminal tail of plant aquaporins that get phosphorylated in vivo in response to environmental stimuli.
Mutant forms of these proteins were expressed in transgenic plants as GFP fusion proteins, and it could be shown that phosphorylation at at least one of the phosphorylation sites is required to target the aquaporin to the plasma membrane.
It was proposed earlier that protein phosphorylation acts as a molecular sorting "switch" within intracellular protein trafficking pathways {1}. In support of such a model, the prominent yeast plasma membrane H+-ATPase PMA1 is phosphorylated at multiple sites during transit to the cell membrane {2}, although specific sites and their role in trafficking could not be established in this early work. Sequence motifs that confer surface expression have been identified by genetic methods and one (SWTY), found in a number of plasma membrane proteins, may operate by recruiting 14-3-3 proteins following phosphorylation at the threonine residue {3}. However, none of the phosphorylation sites in the C-terminus of aquaporins are in an environment that resemble known 14-3-3 binding motifs. References: {1} Herman et al. Cell 1991, 64:425-37 [PMID:1988155]; {2} Chang and Slayman, J Cell Biol 1991, 115:289-95 [PMID:1833410]; {3} Shikano et al. Nat Cell Biol 2005, 7:985-92 [PMID:16155591].
Competing interests: None declared
Palmgren M: "This is an interesting paper in that is shows that phosphorylation at specific sites in..." Evaluation of: [Prak S et al. Multiple phosphorylations in the C-terminal tail of plant plasma membrane aquaporins: role in subcellular trafficking of AtPIP2;1 in response to salt stress. Mol Cell Proteomics. 2008 Jun; 7(6):1019-30; doi: 10.1074/mcp.M700566-MCP200]. Faculty of 1000, 06 Aug 2008. F1000.com/1118895#eval575001
Short form
Palmgren M: 2008. F1000.com/1118895#eval575001
Faculty of 1000 evaluations, dissents and comments for [Prak S et al. Multiple phosphorylations in the C-terminal tail of plant plasma membrane aquaporins: role in subcellular trafficking of AtPIP2;1 in response to salt stress. Mol Cell Proteomics. 2008 Jun; 7(6):1019-30; doi: 10.1074/mcp.M700566-MCP200]. Faculty of 1000, 06 Aug 2008. F1000.com/1118895
Short form
Faculty of 1000: 2008. F1000.com/1118895
Aquaporins form a family of water and solute channel proteins and are present in most living organisms. In plants, aquaporins play an important role in the regulation of root water transport in response to abiotic stresses. In this work, we investigated the role of phosphorylation of plasma membrane intrinsic protein (PIP) aquaporins in the Arabidopsis thaliana root by a combination of quantitative mass spectrometry and cellular biology approaches. A novel phosphoproteomics procedure that involves plasma membrane purification, phosphopeptide enrichment with TiO(2) columns, and systematic mass spectrometry sequencing revealed multiple and adjacent phosphorylation sites in the C-terminal tail of several AtPIPs. Six of these sites had not been described previously. The phosphorylation of AtPIP2;1 at two C-terminal sites (Ser(280) and Ser(283)) was monitored by an absolute quantification method and shown to be altered in response to treatments of plants by salt (NaCl) and hydrogen peroxide. The two treatments are known to strongly decrease the water permeability of Arabidopsis roots. To investigate a putative role of Ser(280) and Ser(283) phosphorylation in aquaporin subcellular trafficking, AtPIP2;1 forms mutated at either one of the two sites were fused to the green fluorescent protein and expressed in transgenic plants. Confocal microscopy analysis of these plants revealed that, in resting conditions, phosphorylation of Ser(283) is necessary to target AtPIP2;1 to the plasma membrane. In addition, an NaCl treatment induced an intracellular accumulation of AtPIP2;1 by exerting specific actions onto AtPIP2;1 forms differing in their phosphorylation at Ser(283) to induce their accumulation in distinct intracellular structures. Thus, the present study documents stress-induced quantitative changes in aquaporin phosphorylation and establishes for the first time a link with plant aquaporin subcellular localization.
DOI: 10.1074/mcp.M700566-MCP200
PMID: 18234664
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