Dimerization of Toc-GTPases at the Chloroplast Protein Import Machinery

AtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery

“…The results indicate that atToc90 directly interacts with atToc33 and suggests that this interaction may contribute to the targeting of atToc90 to the Toc-complex. The interaction between atToc159 and atToc33 has been characterized in detail indicating that the two proteins heterodimerize via their G-domains Weibel et al, 2003). Whether this also applies to the G-domain of atToc90, while it appears likely, needs to be addressed in the future.…”

“…Cytosolic atToc159 is directly targeted to the Toc-complex in a homotypic interaction with atToc33 mediated by the G-domains of the two proteins (Hiltbrunner et al, 2001b;Bauer et al, 2002;Smith et al, 2002;Lee et al, 2003;Weibel et al, 2003). These results are supported by the crystal structure of the pea Toc34 homodimer identifying sequence motifs conserved in both atToc33 and atToc159 which are required for dimerization and chloroplast targeting of soluble atToc159 (Sun et al, 2002;Weibel et al, 2003). These findings suggest that atToc159 and its homologues may function as soluble factors in chloroplast protein import (Hiltbrunner et al, 2001b;Bauer et al, 2002;Smith et al, 2002).…”

“…Recently, we have discovered that atToc159 also exists in an abundant soluble form, partitioning between the outer chloroplast membrane and the cytosol (Hiltbrunner et al, 2001b). Cytosolic atToc159 is directly targeted to the Toc-complex in a homotypic interaction with atToc33 mediated by the G-domains of the two proteins (Hiltbrunner et al, 2001b;Bauer et al, 2002;Smith et al, 2002;Lee et al, 2003;Weibel et al, 2003). These results are supported by the crystal structure of the pea Toc34 homodimer identifying sequence motifs conserved in both atToc33 and atToc159 which are required for dimerization and chloroplast targeting of soluble atToc159 (Sun et al, 2002;Weibel et al, 2003).…”

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

“…Indeed, a critical arginine residue (R133 in psToc34 and R130 in atToc33) was present in the TOC receptor dimer interface. This positional feature, however, is structurally important for dimerization but has little effect on binding and the overall structure of the monomer (Weibel et al , 2003 ), consequently overruling the idea that the monomer of psToc34 or atToc33/34 acts as self-activating GAP. Others have reported that preproteins, specifically the transit peptide, stimulate GTP hydrolysis of the TOC receptors (Jelic et al , 2002 ;Lee et al , 2009b ).…”

“…Hence, a comparable function of the transit peptide and GEF is excluded by the authors as nucleotide exchange is apparently a downstream effect from the transit peptidedependent psToc34/atToc33 dimer dissociation event. Heterodimerization between Toc34 and Toc159 has also been observed biochemically (Wallas et al , 2003 ;Weibel et al , 2003 ;Yeh et al , 2007 ;Rahim et al , 2009 ) and is achieved via conserved arginine residues in Toc34 (R133 in psToc34 and R130 in atToc33) with the G-domain of Toc159 . Thus, homodimerization of the Toc159 receptor is theoretically possible, however, experimental data to support this possibility are currently lacking.…”