Abstract
Mitochondrial transcripts are subject to a wealth of processing mechanisms including cis- and trans-splicing events, as well as base modifications (RNA editing). Hundreds of proteins are required for these processes in plant mitochondria, many of which belong to the pentatricopeptide repeat (PPR) protein superfamily. The structure, localization, and function of these proteins is only poorly understood. Here we present evidence that several PPR proteins are bound to mitoribosomes in plants. A novel complexome profiling strategy in combination with chemical crosslinking has been employed to systematically define the protein constituents of the large and the small ribosomal subunits in the mitochondria of plants. We identified more than 80 ribosomal proteins, which include several PPR proteins and other non-conventional ribosomal proteins. These findings reveal a potential coupling of transcriptional and translational events in the mitochondria of plants. Furthermore, the data indicate an extremely high molecular mass of the "small" subunit, even exceeding that of the "large" subunit.
Highlights
Protein units not directly related to translation may be attached to plant mitoribosomes to confer additional functions to these molecular machines
Protein Correlation Profiling and Complexome Profiling— Separation of protein complexes in combination with LCMS/MS has been successfully employed in the past to identify stable protein complexes, either of total cell extracts or of pre-purified cellular compartments, i.e. organelles
In a bid to characterize low abundant plant mitochondria protein complexes, we here use electrophoretic separation of protein complexes solubilized from isolated organelles
Summary
Protein units not directly related to translation may be attached to plant mitoribosomes to confer additional functions to these molecular machines. Aside from ribosomal RNA-moieties (rRNAs) and dedicated tRNAs, plant mitochondria encode proteins involved in mRNA maturation, translation, cytochrome c maturation and oxidative phosphorylation [1]. Several of these proteins form protein complexes which contain subunits encoded in the nucleus. The components of these complexes are derived from two different genomes, located in the nucleus and in the mitochondria themselves, defining many mitochondrial protein complexes as chimeras Due to their ␣-proteobacterial origin, mitoribosomes largely resemble bacterial 70S ribosomes with respect to their sedimentation behavior, RNA content, and susceptibility to certain antibiotics [2]. Lack the 5S rRNA found in the bacterial LSU, as well as the bacterial 5S rRNA binding proteins [10]
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