On the significance of Toc-GTPase homodimers

  • Precursor protein translocation across the outer chloroplast membrane depends on the action of the Toc complex, containing GTPases as recognizing receptor components. The G domains of the GTPases are known to dimerize. In the dimeric conformation an arginine contacts the phosphate moieties of bound nucleotide in trans. Kinetic studies suggested that the arginine in itself does not act as an arginine finger of a reciprocal GTPase-activating protein (GAP). Here we investigate the specific function of the residue in two GTPase homologues. Arginine to alanine replacement variants have significantly reduced affinities for dimerization compared with wild-type GTPases. The amino acid exchange does not impact on the overall fold and nucleotide binding, as seen in the monomeric x-ray crystallographic structure of the Arabidopsis Toc33 arginine-alanine replacement variant at 2.0A. We probed the catalytic center with the transition state analogue GDP/AlF(x) using NMR and analytical ultracentrifugation. AlF(x) binding depends on the arginine, suggesting the residue can play a role in catalysis despite the non-GAP nature of the homodimer. Two non-exclusive functional models are discussed: 1) the coGAP hypothesis, in which an additional factor activates the GTPase in homodimeric form; and 2) the switch hypothesis, in which a protein, presumably the large Toc159 GTPase, exchanges with one of the homodimeric subunits, leading to activation.

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Metadaten
Author:Patrick KönigGND, Igor-Mislav OrebORCiDGND, Karsten RippeORCiDGND, Claudia Muhle-GollORCiDGND, Irmgard SinningORCiDGND, Enrico SchleiffORCiDGND, Ivo TewsORCiDGND
URN:urn:nbn:de:hebis:30:3-763982
DOI:https://doi.org/10.1074/jbc.M710576200
ISSN:0021-9258
Pubmed Id:https://pubmed.ncbi.nlm.nih.gov/18541539
Parent Title (English):Journal of biological chemistry
Publisher:American Society for Biochemistry and Molecular Biology Publications
Place of publication:Bethesda, Md
Document Type:Article
Language:English
Date of Publication (online):2021/01/04
Year of first Publication:2008
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2024/04/17
Volume:283.2008
Issue:34
Page Number:9
First Page:23104
Last Page:23112
Institutes:Biowissenschaften
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 57 Biowissenschaften; Biologie / 570 Biowissenschaften; Biologie
Sammlungen:Universitätspublikationen
Licence (German):License LogoCreative Commons - CC BY - Namensnennung 4.0 International