Table 1.

Predicted phosphorylation sites on aquaporin 2

Putative phosphorylation site	Kinase	Kinase family	Species
N-terminus
S6	GSK-3 kinaseb	Acidophilic serine/threonine	h,r,m,sh
S10	Clk2 kinasea	Basophilic serine/threonine	r,m,sh
Second intracellular loop
S148	Casein kinase 2b, c	Acidophilic serine/threonine	h,r,m,sh
T159	GSK-3 kinasea, b	Acidophilic serine/threonine	h,r,m
T159	Cdk5 kinasea	Proline-dependent serine/threonine	h,
T159	Cdc2 kinasea	Proline-dependent serine/threonine	h,
S/T*159	P38 MAPKa	Proline-dependent serine/threonine	h,r,m
S/T*159	Erk1 kinasea, b	Proline-dependent serine/threonine	h,r,m
S163	GSK-3 kinasea, b	Acidophilic serine/threonine	h,r,m
C-terminus
S216	PKC-zetaa, h	Basophilic serine/threonine	h,r,m
S229	Casein kinase 2b, c	Acidophilic serine/threonine	h,r,m,sh
S231	PKCc	Basophilic serine/threonine	h,sh
T244	Casein kinase 2a, b, c	Acidophilic serine/threonine	h,r,m,sh
S256	Protein kinase Aa, b, c, d, e	Basophilic serine/threonine	h,r,m,sh
S256	Protein kinase Gg	Basophilic serine/threonine	h,r,m,sh
S256	Calmodulin dependent kinase 2a	Basophilic serine/threonine	h,r,m,sh
S256	Akt kinasea	Basophilic serine/threonine	h,r,m,sh
S256	Clk2 kinasea	Basophilic serine/threonine	h,r,m,sh
S256	Casein kinase 2f	Acidophilic serine/threonine	h,r,m,sh
S261	Cdk5 kinasea	Proline-dependent serine/threonine	h,r,m,sh
S261	Cdc2 kinasea	Proline-dependent serine/threonine	h,r,m,sh
S261	Erk1 kinasea, b	Proline-dependent serine/threonine	h,r,m,sh
S261	p38 kinased	Proline-dependent serine/threonine	h,r,m,sh
S264	Casein kinase 1b	Acidophilic serine/threonine	h,r,m,sh
S264	PKCd	Basophilic serine/threonine	h,r,m,sh
S/T*269	Protein kinase A ??d	Basophilic serine/threonine	h,r,m,sh

^aUsing Scansite [scansite.mit.edu] algorithms, 10 of 14 cytoplasmic serine/threonine residues of aquaporin 2 (AQP2) were designated as potential phosphorylation sites.

^bElm [elm.eu.org] algorithms, 10 of 14 cytoplasmic serine/threonine residues of aquaporin 2 (AQP2) were designated as potential phosphorylation sites.

^cIn addition, Van Balkom et al. [3] proposed and investigated several putative sites by site-directed mutagenesis.

^dHoffert et al. [4] identified several AQP2 phosphorylation sites by phosphoproteomic analysis.

^eKuwahara et al. showed that the AQP2 C-terminus is a subtrate for cAMP-sensitive phosphorylation kinase.

^fUsing a synthetic peptide, Brunati et al. [2] showed that S256 can be phosphorylated by casein kinase II.

^gWe recently showed that an AQP2 C-terminal peptide can be phosphorylated by PKG. Interestingly, some serine/threonine residues are predicted to be phosphorylated by several kinases. For example, S256 is hypothetically phosphorylated by seven different kinases.

^hIt should be noted that S216, a PKC-zeta phosphorylation motif, may be part of the sixth transmembrane domain and consequently cytoplasmic PKC-zeta may be unable to target this residue.

^*Serine in mouse and rat while threonine in human and sheep. GSK, glycogen synthase kinase; h, human; m, mouse; MAP, mitogen activated protein; PKA, protein kinase A; PKC, protein kinase C; PKG, protein kinase G; r, rat; sh, sheep.