Structural and functional analysis of SoPIP2;1 mutants adds insight into plant aquaporin gating.
Artikel i vetenskaplig tidskrift, 2009

Plant plasma membrane aquaporins facilitate water flux into and out of plant cells, thus coupling their cellular function to basic aspects of plant physiology. Posttranslational modifications of conserved phosphorylation sites, changes in cytoplasmic pH and the binding of Ca(2+) can regulate water transport activity by gating the plasma membrane aquaporins. A structural mechanism unifying these diverse biochemical signals has emerged for the spinach aquaporin SoPIP2;1, although several questions concerning the opening mechanism remain. Here, we describe the X-ray structures of the S115E and S274E single SoPIP2;1 mutants and the corresponding double mutant. Phosphorylation of these serines is believed to increase water transport activity of SoPIP2;1 by opening the channel. However, all mutants crystallised in a closed conformation, as confirmed by water transport assays, implying that neither substitution fully mimics the phosphorylated state. Nevertheless, a half-turn extension of transmembrane helix 1 occurs upon the substitution of Ser115, which draws the C(alpha) atom of Glu31 10 A away from its wild-type conformation, thereby disrupting the divalent cation binding site involved in the gating mechanism. Mutation of Ser274 disorders the C-terminus but no other significant conformational changes are observed. Inspection of the hydrogen-bond interactions within loop D suggested that the phosphorylation of Ser188 may also produce an open channel, and this was supported by an increased water transport activity for the S188E mutant and molecular dynamics simulations. These findings add additional insight into the general mechanism of plant aquaporin gating.

phoshorylation

X-ray crystallography

membrane protein

gating

plant aquaporin

Författare

Anna Maria Nyblom

Chalmers, Kemi- och bioteknik, Molekylär mikroskopi

Anna Frick

Göteborgs universitet

Yi Wang

University of Illinois

Mikael Ekvall

Göteborgs universitet

Karin Hallgren

Göteborgs universitet

Kristina Hedfalk

Göteborgs universitet

Richard Neutze

Göteborgs universitet

Emad Tajkhorshid

University of Illinois

Susanna Törnroth-Horsefield

Göteborgs universitet

Journal of molecular biology

1089-8638 (ISSN)

Vol. 387 653-68

Ämneskategorier

Kemi

DOI

10.1016/j.jmb.2009.01.065

PubMed

19302796