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The plant Rab18 dehydrin - a disordered stressed induced conditional peripheral membrane protein. Specific interaction with PI(4,5)P2
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.ORCID iD: 0000-0003-2749-2415
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The Arabidosis dehydrin Rab18 is expressed in response to drought and the phytohormone ABA. As a clue to a general dehydrin function, some dehydrins are found to interact in an orderly manner with negatively-charged lipids, supporting the idea of a key role in safeguarding membrane integrity. Interaction between dehydrins and membranes studied so far has been driven by general electrostatic attractions. Here, we report on specific binding of Rab18 with inositol lipids, especially PI(4,5)P2. This binding is not purely under the control of global protein electrostatics since Rab18 fails to bind to lipid vesicles with a high negative net charge (DOPC:DOPG, 3:1). Instead, Rab18 binds strongly to inositol lipids even at low negative vesicle net charge (i.e. DOPC:DOPI(4,5)P2, 98:2). Further, Rab18 show a high specificity to inositol lipids with a phosphate in the 5th position on the inositol ring i.e. PI(5)P and PI(4,5)P2 whereas a phosphate at 3rd position restrains Rab18 binding (i.e. PI(4,5)P2>PI(3,5)P2>PI(3,4)P2 and PI(5)P>> PI(3)P). Moreover, Rab18 specificity to inositol lipids is mainly augmented by the Arg in the protein sequence and when all six Arg are replaced by Lys is the binding of Rab18 to PI(4,5)P2 almost abolished. The two Arg preceding the first K-seg (Rab18Arg125-126) are key residues in binding PI(4,5)P2 and the mechanistic implication of these Arg is elucidated. We put forward the idea that Rab18 is a conditional peripheral membrane protein that sense and respond to lipid alterations at membrane surfaces during stress. Moreover, by binding to PI(4,5)P2 Rab18 could take part in the regulation of different cellular processes, showing a new role of dehydrins as regulators of plant stress. A possible role of Rab18 in the regulation of ABA induced stomata movements are presented. 

National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-136030OAI: oai:DiVA.org:su-136030DiVA: diva2:1050498
Available from: 2016-11-29 Created: 2016-11-29 Last updated: 2017-01-10Bibliographically approved
In thesis
1. Molecular properties of disordered plant dehydrins: Membrane interaction and function in stress
Open this publication in new window or tab >>Molecular properties of disordered plant dehydrins: Membrane interaction and function in stress
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dehydrins are intrinsically disordered plant stress-proteins. Repetitively in their sequence are some highly conserved stretches of 7-17 residues, the so called K-, S-, Y- and lysine rich segments. This thesis aims to give insight into the possible role dehydrins have in the stressed plant cell with main focus on membrane interaction and protection. The work includes four recombinant dehydrins from the plant Arabidopsis thaliana: Cor47 (SK3), Lti29 (SK3), Lti30 (K6) and Rab18 (Y2SK2).

Initially, we mimicked crowded cellular environment in vitro to verify that dehydrins are truly disordered proteins. Thereafter, the proposal that the compulsory K-segment determines membrane binding was tested. Experiments show that only Lti30 and Rab18 bind, whereas Cor47 and Lti29 does not. As Lti30 and Rab18 binds they assembles vesicles into clusters in vitro, a feature used to characterize the interaction. From this it was shown that membrane binding of Lti30 is electrostatic and determined by global as well as local charges. Protonation of histidine pairs flanking the K-segments works as an on/off-binding switch. By NMR studies it was shown that the K-segments form a dynamic α-helix upon binding, so called disorder-to-order behaviour. Also, dehydrins electrostatic interaction with lipids can be further tuned by posttranslational phosphorylation or coordination of calcium and zinc ions.

Finally, specific binding of Rab18 to inositol lipids, mainly PI(4,5)P2, is reported. The interaction is mainly coordinated by two arginines neighboring one of the K-segments. In conclusion, the K-segments are indeed involved in the binding of dehydrins to membrane but only in combination with extensions (Lti30) or modified (Rab18). 

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2016. 62 p.
Keyword
abiotic stress, dehydrin, intrinsically disordered proteins, Lea-proteins, phospholipids
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-136033 (URN)978-91-7649-065-5 (ISBN)978-91-7649-599-5 (ISBN)
Public defence
2017-01-13, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2016-12-20 Created: 2016-11-29 Last updated: 2016-12-21Bibliographically approved

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