Abstract
Defects in mitochondrial ribosomal proteins (MRPs) cause various diseases in humans. Because of the essential role of MRPs in synthesizing the essential subunits of oxidative phosphorylation (OXPHOS) complexes, identifying all of the protein components involved in the mitochondrial translational machinery is critical. Initially, we identified 79 MRPs; however, identifying MRPs with no clear homologs in bacteria and yeast mitochondria was challenging, due to limited availability of expressed sequence tags (ESTs) in the databases available at that time. With the improvement in genome sequencing and increased sensitivity of mass spectrometry (MS)-based technologies, we have established four previously known proteins as MRPs and have confirmed the identification of ICT1 (MRP58) as a ribosomal protein. The newly identified MRPs are MRPS37 (Coiled-coil-helix-coiled-coil-helix domain containing protein 1-CHCHD1), MRPS38 (Aurora kinase A interacting protein1, AURKAIP1), MRPS39 (Pentatricopeptide repeat-containing protein 3, PTCD3), in the small subunit and MRPL59 (CR-6 interacting factor 1, CRIF1) in the large subunit. Furthermore, we have demonstrated the essential roles of CHCHD1, AURKAIP1, and CRIF1in mitochondrial protein synthesis by siRNA knock-down studies, which had significant effects on the expression of mitochondrially encoded proteins.
Highlights
Mammalian mitochondria use oxidative phosphorylation (OXPHOS) to provide more than 90% of the ATP used for energy by cells
IDENTIFICATION OF 55S RIBOSOMAL PROTEINS BY TANDEM MASS SPECTROMETRY The majority of the protein components of mammalian mitochondrial ribosomes were identified by our group, as well as several other groups, a decade ago using proteomics strategies (Goldschmidt-Reisin et al, 1998; Graack et al, 1999; Koc et al, 1999, 2000, 2001a,b; O’Brien et al, 1999)
The protein compositions of the 55S samples prepared under the two different salt and detergent conditions were compared by SDS-PAGE (Figure S1)
Summary
Mammalian mitochondria use oxidative phosphorylation (OXPHOS) to provide more than 90% of the ATP used for energy by cells. We re-evaluated protein components of the mammalian mitochondrial ribosome using mass spectrometry (MS)-based proteomics and have established that five previously known mitochondrial proteins are components of the mitochondrial ribosome. These proteins are coiled-coilhelix-coiled-coil-helix domain containing protein 1 (CHCHD1), aurora kinase A interacting protein 1 (AURKAIP1), pentatricopeptide repeat-containing protein 3 (PTCD3), immature colon carcinoma transcript 1 protein (ICT1) and CR-6 interacting factor 1 [CRIF1, known as growth arrest and DNA-damageinducible proteins-interacting protein 1 (Gadd45GIP1)]. We further confirmed the specific roles for CHCHD1, AURKAIP1, and CRIF1 in mitochondrial translation by siRNA knock-down studies in human cell lines
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