Phosphorylation of plasma membrane aquaporins from Zea mays
(2005)
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- Authors
- Supervisors
- Chaumont, François
- Abstract
- Aquaporins (AQP) are channel proteins that facilitate transmembrane water movement. Plant aquaporins belonging to the plasma membrane intrinsic protein subfamily (PIP) are divided into two sequence-related subgroups, referred to as PIP1 and PIP2. All plant PIP2 proteins have been shown to have high water channel activity when expressed in Xenopus oocytes, whereas PIP1 proteins are often inactive or have low water channel activity. Plant AQPs can be regulated by phosphorylation and dephosphorylation. Here, we show that PIPs from one-week-old maize shoots are phosphorylated in vitro and in vivo on serine residue(s) by a calcium-dependent kinase associated with the plasma membrane fraction. Mass spectrometry allowed us to identify phosphorylated peptides corresponding to the C-terminus of (i) ZmPIP2;1, ZmPIP2;2 and/or ZmPIP2;7, (ii) ZmPIP2;3 and/or ZmPIP2;4, (iii) ZmPIP2;6 together with (iv) a phosphorylated peptide located at the N-terminus of ZmPIP1;1, ZmPIP1;2, ZmPIP1;3 and/or ZmPIP1;4. The role of phosphorylation on water channel activity of ZmPIP2;1 wild-type and mutant forms was studied in detail in Xenopus oocytes. We first showed that expression of ZmPIP2;1 significantly increased the osmotic water permeability coefficient (Pf) of the oocyte plasma membrane indicating that this protein is a functional water channel. Activation of endogenous protein kinase A increased the osmotic water permeability coefficient of oocytes expressing ZmPIP2;1 suggesting that phosphorylation regulates its channel activity. Mutation of S126, a putative phosphorylated serine conserved in all plant PIPs, into alanine decreased ZmPIP2;1 activity by 50 %, without affecting its targeting to the plasma membrane. Mutation of S285, which is phosphorylated in planta, into alanine or glutamate did not modify the protein water channel activity. These results indicate that, in oocytes, S126 plays an important role in ZmPIP2;1 activity and that phosphorylation of S285 is not essential for its activity. ...
- Affiliations
Citations
Van Wilder, V. (2005). Phosphorylation of plasma membrane aquaporins from Zea mays. https://hdl.handle.net/2078.5/97980