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Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33

Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33
Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33
GTPases act as molecular switches to control many cellular processes, including signalling, protein translation and targeting. Switch activity can be regulated by external effector proteins or intrinsic properties, such as dimerization. The recognition and translocation of pre-proteins into chloroplasts [via the TOC/TIC (translocator at the outer envelope membrane of chloroplasts/inner envelope membrane of chloroplasts)] is controlled by two homologous receptor GTPases, Toc33 and Toc159, whose reversible dimerization is proposed to regulate translocation of incoming proteins in a GTP-dependent manner. Toc33 is a homodimerizing GTPase. Functional analysis suggests that homodimerization is a key step in the translocation process, the molecular functions of which, as well as the elements regulating this event, are largely unknown. In the present study, we show that homodimerization reduces the rate of nucleotide exchange, which is consistent with the observed orientation of the monomers in the crystal structure. Pre-protein binding induces a dissociation of the Toc33 homodimer and results in the exchange of GDP for GTP. Thus homodimerization does not serve to activate the GTPase activity as discussed many times previously, but to control the nucleotide-loading state. We discuss this novel regulatory mode and its impact on the current models of protein import into the chloroplast.
dimeric GTPase, GDP-dissociation-inhibitor function (GDI function), G-protein, protein translocation, substrate-based regulation
1470-8728
313-319
Oreb, Mislav
85bcf606-2b7c-4362-a88f-b99bf6cbe748
Höfle, Anja
d0ed5ed6-54c6-47e8-8e1a-db9244d03e23
Koenig, Patrick
e03428c5-67ef-4df4-9310-77190d216517
Sommer, Maik S.
f124d403-312a-4f3a-84e9-d61e5ecba1a1
Sinning, Irmgard
fbc3f199-8a3b-47a6-9ee7-00bfc472e079
Wang, Fei
d74a565b-35c9-43af-95ba-06782f81a561
Tews, Ivo
9117fc5e-d01c-4f8d-a734-5b14d3eee8dd
Schnell, Danny J.
02916bdc-8566-4ce5-b69a-b911b3ce1f7e
Schleiff, Enrico
119114bb-9cbb-45e9-a161-db45b1e9f4ba
Oreb, Mislav
85bcf606-2b7c-4362-a88f-b99bf6cbe748
Höfle, Anja
d0ed5ed6-54c6-47e8-8e1a-db9244d03e23
Koenig, Patrick
e03428c5-67ef-4df4-9310-77190d216517
Sommer, Maik S.
f124d403-312a-4f3a-84e9-d61e5ecba1a1
Sinning, Irmgard
fbc3f199-8a3b-47a6-9ee7-00bfc472e079
Wang, Fei
d74a565b-35c9-43af-95ba-06782f81a561
Tews, Ivo
9117fc5e-d01c-4f8d-a734-5b14d3eee8dd
Schnell, Danny J.
02916bdc-8566-4ce5-b69a-b911b3ce1f7e
Schleiff, Enrico
119114bb-9cbb-45e9-a161-db45b1e9f4ba

Oreb, Mislav, Höfle, Anja, Koenig, Patrick, Sommer, Maik S., Sinning, Irmgard, Wang, Fei, Tews, Ivo, Schnell, Danny J. and Schleiff, Enrico (2011) Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33. Biochemical Journal, 436 (2), 313-319. (doi:10.1042/BJ20110246). (PMID:21568939)

Record type: Article

Abstract

GTPases act as molecular switches to control many cellular processes, including signalling, protein translation and targeting. Switch activity can be regulated by external effector proteins or intrinsic properties, such as dimerization. The recognition and translocation of pre-proteins into chloroplasts [via the TOC/TIC (translocator at the outer envelope membrane of chloroplasts/inner envelope membrane of chloroplasts)] is controlled by two homologous receptor GTPases, Toc33 and Toc159, whose reversible dimerization is proposed to regulate translocation of incoming proteins in a GTP-dependent manner. Toc33 is a homodimerizing GTPase. Functional analysis suggests that homodimerization is a key step in the translocation process, the molecular functions of which, as well as the elements regulating this event, are largely unknown. In the present study, we show that homodimerization reduces the rate of nucleotide exchange, which is consistent with the observed orientation of the monomers in the crystal structure. Pre-protein binding induces a dissociation of the Toc33 homodimer and results in the exchange of GDP for GTP. Thus homodimerization does not serve to activate the GTPase activity as discussed many times previously, but to control the nucleotide-loading state. We discuss this novel regulatory mode and its impact on the current models of protein import into the chloroplast.

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More information

e-pub ahead of print date: 24 March 2011
Published date: 1 June 2011
Keywords: dimeric GTPase, GDP-dissociation-inhibitor function (GDI function), G-protein, protein translocation, substrate-based regulation
Organisations: Centre for Biological Sciences

Identifiers

Local EPrints ID: 200227
URI: http://eprints.soton.ac.uk/id/eprint/200227
ISSN: 1470-8728
PURE UUID: 2e5646bb-b61b-409c-8f93-0ab903b6e2d5
ORCID for Ivo Tews: ORCID iD orcid.org/0000-0002-4704-1139

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Date deposited: 24 Oct 2011 14:02
Last modified: 20 Jul 2019 00:46

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