A plant outer mitochondrial membrane protein with high amino acid sequence identity to a chloroplast protein import receptor

Abstract

We have identi¢ed a novel protein on the outer membrane of Arabidopsis thaliana mitochondria. This protein displays 67% sequence identity with the 64 kDa translocase of the outer envelope membrane of chloroplasts (Toc). A mitochondrial localisation for this protein was determined by (i) its presence in the proteome of highly puri¢ed Arabidopsis mitochondria, (ii) Western blot analysis with antibodies to Toc64 from pea that indicate its presence in Arabidopsis and pea mitochondria, (iii) green £uorescent protein fusion proteins that indicate an exclusive mitochondrial localisation for this protein, and (iv) expression pro¢les in various tissue types and during development that are more similar to translocase of the outer mitochondrial membrane components than to chloroplastic Toc components. Thus Arabidopsis mitochondria contain a protein with high sequence identity to a plastid protein import receptor.

Subcellular localization and tissue specific expression of amidase 1 from Arabidopsis thaliana

“…Nevertheless, these data are not sufficient to prove a cytoplasmic localization ñor do they exelude AMI1 from organdíes, which could have been disrupted during the preparation procedure, thus releasing their soluble proteins. Some recent publications (Vojta et al 2004;Chew et al 2004) assumed a possible plastidial or mitochondrial localization of AMI1, associating AMI1 with two proteins, Toc64-III and mtOM64, mainly based on their primary amino acid sequence homology, emphasized by the clustering of the three proteins into one branch of a phylogenetic tree (Fig. Ib).…”

“…The A. thaliana amidase-signature family comprises seven different members each encoded by a different gene from which only two proteins, AMIl (Pollmann et al 2003) and a fatty acid amide hydrolase (FAAH; Shrestha et al 2003), were characterized for their enzymatic activity. The third isoform (At5g09420) seems to be localized in the outer mitochondrial membrane in complex with a protein translocase (Chew et al 2004) and a fourth one (At3gl7970) has been found associated with proteins of the chloroplast Toc-complex after protein cross-linking (Sohrt and Solí 2000). No information is available so far about the function and expression of the other three polypeptides.…”

The Protein Translocon of the Plastid Envelopes

“…The functional differences of the Toc159 family remain elusive. For Toc75, four members of the gene family were proposed, namely Toc75-I, -III, -IV, and -V, and for Toc64, three members of the gene family are known, namely Toc64-I, -III, and -V. However, Toc64-V is clearly located in mitochondria and not in chloroplasts (17).…”

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

“…TPR domaincontaining proteins, which are found in all organisms in cellular compartments are known to contribute to posttranslational protein import by the interaction with cytosolic chaperones (Feldheim and Schekman , 1994 ;Young et al , 2003 ;Schlegel et al , 2007 ). Post-translational protein translocation involving TPR-containing proteins and cytosolic chaperones has been well documented for mammalian and yeast receptors Tom20, Tom34 and Tom70 (Abe et al , 2000 ;Young et al , 2003 ;Chew et al , 2004 ;Saitoh et al , 2007 ;Faou and Hoogenraad , 2012 ). In plants, apart from Toc64, TPR-mediated preprotein translocation has thus far been reported for the mitochondrial outer envelope protein, OM64 and recently, the endoplasmic reticulum (ER) TPR-docking protein, AtTPR7.…”