InterPro domain: IPR005690

This entry represents the translocase of chloroplast 159 family of proteins (Tocs), GTPases involved in protein precursor import into chloroplasts, which recognise chloroplast-destined precursor proteins and regulate their presentation to the translocation channel through GTP hydrolysis [ 1 ]. They have three domains: the N-terminal A-domain is acidic, repetitive, weakly conserved, readily removed by proteolysis during chloroplast isolation, not required for protein translocation [ 2 , 3 ], and the other domains are designated G (GTPase) and M (membrane anchor) [ 3 ]. The signature for this family includes most of the G domain and all of M. There are at least two distinct Toc159 subtypes, Toc159 and Toc132/Toc120. Toc159 is expressed in young photosynthetic tissues and seems to be specialised in the import of nuclear encoded photosynthetic preproteins from the cytoplasm to the chloroplast, whereas Toc132/Toc120 are expressed relatively prominent in nonphotosynthetic tissues and seem to be specialised in the import of nuclear encoded non-photosynthetic preproteins from the cytoplasm to the chloroplast [ 3 ].

1. Functional specialization amongst the Arabidopsis Toc159 family of chloroplast protein import receptors. Plant Cell 16, 2059-77
2. Initial binding of preproteins involving the Toc159 receptor can be bypassed during protein import into chloroplasts. Plant Physiol. 122, 813-22