Human mitochondrial SUV3 and polynucleotide phosphorylase form a 330-kDa heteropentamer to cooperatively degrade double-stranded RNA with a 3'-to-5' directionality.
Efficient turnover of unnecessary and misfolded RNAs is critical for maintaining the integrity and function of the mitochondria. The mitochondrial RNA degradosome of budding yeast (mtEXO) has been recently studied and characterized; yet no RNA degradation machinery has been identified in the mammalian mitochondria. In this communication, we demonstrated that purified human SUV3 (suppressor of Var1 3) dimer and polynucleotide phosphorylase (PNPase) trimer form a 330-kDa heteropentamer that is capable of efficiently degrading double-stranded RNA (dsRNA) substrates in the presence of ATP, a task the individual components cannot perform separately. The configuration of this complex is similar to that of the core complex of the E. coli RNA degradosome lacking RNase E but very different from that of the yeast mtEXO. The hSUV3-hPNPase complex prefers substrates containing a 3' overhang and degrades the RNA in a 3'-to-5' directionality. Deleting a short stretch of amino acids (positions 510-514) compromises the ability of hSUV3 to form a stable complex with hPNPase to degrade dsRNA substrates but does not affect its helicase activity. Furthermore, two additional hSUV3 mutants with abolished helicase activity because of disrupted ATPase or RNA binding activities were able to bind hPNPase. However, the resulting complexes failed to degrade dsRNA, suggesting that an intact helicase activity is essential for the complex to serve as an effective RNA degradosome. Taken together, these results strongly suggest that the complex of hSUV3-hPNPase is an integral entity for efficient degradation of structured RNA and may be the long sought RNA-degrading complex in the mammalian mitochondria.
Wang
Dennis Ding-Hwa
DD
Department of Biological Chemistry, University of California, Irvine, California 92697, USA. whlee@uci.edu
Shu
Zhanyong
Z
Lieser
Scot A
SA
Chen
Phang-Lang
PL
Lee
Wen-Hwa
WH
D000255:Adenosine Triphosphate / Q000494:pharmacology; D019943:Amino Acid Substitution / Q000187:drug effects; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D005095:Exoribonucleases / Q000378:metabolism*; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D008954:Models, Biological; D008970:Molecular Weight; D050505:Mutant Proteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D012330:RNA, Double-Stranded / Q000737:chemistry* / Q000378:metabolism*; D024101:Mitochondrial Proteins
D000255:Adenosine Triphosphate; D053487:DEAD-box RNA Helicases; D005095:Exoribonucleases; D050505:Mutant Proteins; D012330:RNA, Double-Stranded; C476417:PNPT1 protein, human; D024101:Mitochondrial Proteins; C469673:SUPV3L1 protein, human