Phosphorylation regulates the assembly of chloroplast import machinery

Oreb, Mislav; Höfle, Anja; Mirus, Oliver; Schleiff, Enrico

doi:10.1093/jxb/ern095

Cited by 26 publications

(36 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This observation, however, only occurs at an early developmental stage under heterotrophic growth conditions, correlating nicely with the requirement for atToc33 in the early steps of chloroplast biogenesis (Kubis et al , 2004 ). More recently, phosphorylation of atToc33 was reported to negatively regulate its homodimerization and heterodimerization with atToc159 as well as its assembly into the TOC core complex (Oreb et al , 2008 ) .…”

Section: The Pivotal Role Of Phosphorylation On Toc Receptorssupporting

confidence: 52%

“…Since both isoforms acted in distinct targeting pathways involved in transporting specific subsets of proteins (see below), this observation postulated that the different receptors within the distinct TOC complexes might be differentially regulated. Phosphorylation specifically imposes a negative influence on the TOC receptors, particularly their GTPase activity (Sveshnikova et al , 2000 ;Fulgosi and Soll , 2002 ;Jelic et al , 2002 ) and the assembly of Toc34 with the TOC core complex into the outer membrane (Oreb et al , 2008 ).…”

Section: The Pivotal Role Of Phosphorylation On Toc Receptorsmentioning

confidence: 99%

See 1 more Smart Citation

The gateway to chloroplast: re-defining the function of chloroplast receptor proteins

Chang¹,

Soll²,

Bölter³

2012

Biological Chemistry

View full text Add to dashboard Cite

: Chloroplast biogenesis often requires a tight orchestration between gene expression (both plastidial and nuclear) and translocation of ~ 3000 nuclear-encoded proteins into the organelle. Protein translocation is achieved via two multimeric import machineries at the outer (TOC) and inner (TIC) envelope of chloroplast, respectively. Three components constitute the core element of the TOC complex: a β -barrel protein translocation channel Toc75 and two receptor constituents, Toc159 and Toc34. A diverse set of distinct TOC complexes have recently been characterized and these diversified TOC complexes have evolved to coordinate the translocation of differentially expressed proteins. This review aims to describe the recent discoveries relating to the typical characteristics of these distinct TOC complexes, particularly the receptor constituents, which are the main contributors for TOC complex diversification.

show abstract

Section: The Pivotal Role Of Phosphorylation On Toc Receptorssupporting

confidence: 52%

Section: The Pivotal Role Of Phosphorylation On Toc Receptorsmentioning

confidence: 99%

The gateway to chloroplast: re-defining the function of chloroplast receptor proteins

Chang¹,

Soll²,

Bölter³

2012

Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…The K d of the atToc33 dimer is about 1 order of magnitude higher than that for psToc34. Both K d values are in the submillimolar range (25,27). Although these figures, determined for the isolated GTPase, seem high, dimerization may still occur in the physiological context on the membrane or within the Toc complex via elevated local concentrations.…”

Section: Discussionmentioning

confidence: 85%

“…The functional homologue atToc33 from Arabidopsis thaliana (14,26) is a monomer in both nucleotide loading states (16,25). Both GTPases can homodimerize in solution (15,16,25), but atToc33 has a lower association constant compared with psToc34 (16,25,27).…”

mentioning

confidence: 99%

On the Significance of Toc-GTPase Homodimers

Koenig

Oreb²,

Rippe

et al. 2008

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

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 2.0 Å . 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.

show abstract

“…Thus, the POTRA domain might regulate the GTPase activity of the TOC receptors, because this domain provides a Toc33 binding site (30). This would also explain why Toc33 has to be released from the complex after phosphorylation, which is thought to inactivate the receptor (54). Alternatively or in addition, the POTRA domains with their affinity for precursor proteins (30) could interact with the two known receptors in the perception of the targeting signal in general.…”

Section: Impact Of the Cytosolic Potra Domain On The Model Of Proteinmentioning

confidence: 99%

Chloroplast Omp85 proteins change orientation during evolution

Sommer

Daum

Groß

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

The majority of outer membrane proteins (OMPs) from Gramnegative bacteria and many of mitochondria and chloroplasts are β-barrels. Insertion and assembly of these proteins are catalyzed by the Omp85 protein family in a seemingly conserved process. All members of this family exhibit a characteristic N-terminal polypeptide-transport-associated (POTRA) and a C-terminal 16-stranded β-barrel domain. In plants, two phylogenetically distinct and essential Omp85's exist in the chloroplast outer membrane, namely Toc75-III and Toc75-V. Whereas Toc75-V, similar to the mitochondrial Sam50, is thought to possess the original bacterial function, its homolog, Toc75-III, evolved to the pore-forming unit of the TOC translocon for preprotein import. In all current models of OMP biogenesis and preprotein translocation, a topology of Omp85 with the POTRA domain in the periplasm or intermembrane space is assumed. Using selfassembly GFP-based in vivo experiments and in situ topology studies by electron cryotomography, we show that the POTRA domains of both Toc75-III and Toc75-V are exposed to the cytoplasm. This unexpected finding explains many experimental observations and requires a reevaluation of current models of OMP biogenesis and TOC complex function.

show abstract

Phosphorylation regulates the assembly of chloroplast import machinery

Cited by 26 publications

References 34 publications

The gateway to chloroplast: re-defining the function of chloroplast receptor proteins

The gateway to chloroplast: re-defining the function of chloroplast receptor proteins

On the Significance of Toc-GTPase Homodimers

Chloroplast Omp85 proteins change orientation during evolution

Contact Info

Product

Resources

About