Mba1, a membrane-associated ribosome receptor in mitochondria

Abstract

The genome of mitochondria encodes a small number of very hydrophobic polypeptides that are inserted into the inner membrane in a cotranslational reaction. The molecular process by which mitochondrial ribosomes are recruited to the membrane is poorly understood. Here, we show that the inner membrane protein Mba1 binds to the large subunit of mitochondrial ribosomes. It thereby cooperates with the C‐terminal ribosome‐binding domain of Oxa1, which is a central component of the insertion machinery of the inner membrane. In the absence of both Mba1 and the C‐terminus of Oxa1, mitochondrial translation products fail to be properly inserted into the inner membrane and serve as substrates of the matrix chaperone Hsp70. We propose that Mba1 functions as a ribosome receptor that cooperates with Oxa1 in the positioning of the ribosome exit site to the insertion machinery of the inner membrane.

Yeast AEP3p Is an Accessory Factor in Initiation of Mitochondrial Translation

“…RMD9 was independently isolated as a high-copy suppressor of a respiratory-deficient oxa1 mutant and was shown to control the processing and/or stability of several mitochondrial mRNAs (50). These data are consistent with the inner membrane localization of most of the mitochondrial gene expression machinery, including ribosomes (51,52), translational activators (53), RNA processing and stability factors (24,54,55), and even RNA polymerase (54,56). Nouet et al (50) have proposed that Rmd9p delivers mRNAs to the inner membrane-localized ribosomes for translation and insertion of the nascent proteins into the membrane.…”

Mss51 and Ssc1 Facilitate Translational Regulation of Cytochrome c Oxidase Biogenesis

“…In this complex, Ssc1 could remain bound to Cox1 to maintain its proper folding during insertion or to present it to matrix-localized proteolytic systems in the case of unproductive folding that would prevent membrane insertion. Consistently, cells lacking the Mba1 ribosomal receptor or harboring a mutant Oxa1 variant, in which Cox1 is more exposed to the hydrophilic matrix milieu than wild-type cells, display a more prominent association of Cox1 and Ssc1 (38). The release of Ssc1/Mss51/Cox1/Cox14 from its complex with the translational machinery is promoted by the presence of ATP and does not seem to necessarily require ATP hydrolysis: it was equally promoted by ATP and AMP-PNP in ⌬cox11 mitochondria although it was significantly enhanced by Mdj1 overexpression in ⌬coa1 cells.…”

“…The accumulation of Mss51 in the heavier fractions was sensitive to both 50 g/ml puromycin, which induces the release of unfinished polypeptide chains, and to high RNase concentrations (600 U/ml), which fully disrupt the integrity of the ribosomes (38). Under these conditions most Mss51 from ⌬cox11 mitochondria accumulated in the 450-kDa complex (Fig.…”

Translation Initiation inSaccharomyces cerevisiaeMitochondria: Functional Interactions Among Mitochondrial Ribosomal Protein Rsm28p, Initiation Factor 2, Methionyl-tRNA-Formyltransferase and Novel Protein Rmd9p

“…The Oxa1p C-terminal domain is exposed on the matrix side of the membrane and interacts with mitochondrial ribosomes, apparently facilitating cotranslational insertion of newly synthesized proteins (Jia et al 2003;Szyrach et al 2003;Ott et al 2006).…”