The yeast protein Mam33 functions in the assembly of the mitochondrial ribosome

Abstract

Mitochondrial ribosomes are functionally specialized for the synthesis of several essential inner membrane proteins of the respiratory chain. Although remarkable progress has been made toward understanding the structure of mitoribosomes, the pathways and factors that facilitate their biogenesis remain largely unknown. The long unstructured domains of unassembled ribosomal proteins are highly prone to misfolding and often require dedicated chaperones to prevent aggregation. To date, chaperones that ensure safe delivery to the assembling ribosome have not been identified in the mitochondrion. In this study, a respiratory synthetic lethality screen revealed a role for an evolutionarily conserved mitochondrial matrix protein called Mam33 in Saccharomyces cerevisiae mitoribosome biogenesis. We found that the absence of Mam33 results in misassembled, aggregated ribosomes and a respiratory lethal phenotype in combination with other ribosome-assembly mutants. Using sucrose gradient sedimentation, native affinity purifications, in vitro binding assays, and SILAC-based quantitative proteomics, we found that Mam33 does not associate with the mature mitoribosome, but directly binds a subset of unassembled large subunit proteins. Based on these data, we propose that Mam33 binds specific mitoribosomal proteins to ensure proper assembly.

YBEY is an essential biogenesis factor for mitochondrial ribosomes

“…It is, therefore, tempting to hypothesize the existence of a YBEY-mediated crosstalk between the SSU and LSU biogenesis pathways. Interestingly, the yeast p32 homologue has recently been shown to participate in LSU assembly ( 106 ); due to its negative charge, it binds several LSU proteins and prevents their aggregation. Thus, it appears conceivable that the effect of YBEY KO on the mitochondrial LSU is p32-mediated, and indeed the association of p32 with the LSU was significantly decreased in YBEY KO cells (Figure 6G ).…”

YBEY is an essential biogenesis factor for mitochondrial ribosomes

“…It is, therefore, tempting to hypothesise the existence of a YBEY-mediated crosstalk between the SSU and LSU biogenesis pathways. Interestingly, the yeast p32 homologue has recently been shown to participate in LSU assembly (102); due to its negative charge, it binds several LSU proteins and prevents their aggregation. Thus, it appears conceivable that the effect of YBEY KO on the mitochondrial LSU is p32-mediated, and indeed the association of p32 with the LSU was significantly decreased in YBEY KO cells ( Figure 6G).…”

GC1qR Cleavage by Caspase-1 Drives Aerobic Glycolysis in Tumor Cells

“…Thus, augmented gC1qR levels correlate with poor prognosis in cancer patients ( 15 – 21 ). Until now, it is assumed that mitochondrial gC1qR protein maintains mitochondria function by regulating mitochondrial protein translation ( 22 , 23 ). Of note, while gC1qR is mainly localized to the mitochondria via the presence of an N -terminal mitochondrial leader sequence in the protein ( 22 ), gC1qR is also present in other subcellular compartments and can be observed on the cell surface of distinct leukocytes ( 11 , 24 ).…”