TY  - JOUR
A1  - König, Patrick
A1  - Oreb, Igor-Mislav
A1  - Rippe, Karsten
A1  - Muhle-Goll, Claudia
A1  - Sinning, Irmgard
A1  - Schleiff, Enrico
A1  - Tews, Ivo
T1  - On the significance of Toc-GTPase homodimers
T2  - Journal of biological chemistry
N2  - 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.
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/76398
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-763982
SN  - 0021-9258
VL  - 283.2008
IS  - 34
SP  - 23104
EP  - 23112
PB  - American Society for Biochemistry and Molecular Biology Publications
CY  - Bethesda, Md
ER  -