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Structural and biochemical charaterization of the C. elegans SMG8-SMG9 core complex
Structural and biochemical charaterization of the C. elegans SMG8-SMG9 core complex
Nonsense mediated mRNA decay (NMD) is an important mRNA quality control pathway conserved in eukaryotes. NMD targets aberrant mRNAs carrying premature stop codons (PTCs) for rapid degradation, preventing the accumulation of C-terminally truncated protein products that would otherwise be toxic to cells. NMD involves the concerted action of several trans-acting factors and it is a highly regulated process. A decisive event to trigger NMD in metazoans is the phosphorylation of the RNA helicase UPF1 by the SMG1 kinase. SMG8 and SMG9 form a heterodimer that interacts with SMG1 and inhibits its kinase activity. In recent years, electron microscopy studies of the human SMG1-SMG8-SMG9 complex provided low-resolution structural information that revealed the overall architecture of this complex. Still not much is known about the structure and function of SMG8 and SMG9 and how they interact with each other as well as with SMG1. In this thesis, I used biochemical approaches to identify the core of a SMG8-SMG9 complex amenable to crystallization and determined its three-dimensional structure at the resolution of 2.5 Å. I found that the C. elegans SMG8-SMG9 core complex resembles a G-domain heterodimer with a potentially active subunit (SMG9) and an inactive subunit (SMG8). Following this result, I characterized the nucleotide-binding properties of SMG-SMG9 using biophysical and structural methods. Fitting the atomic model in a previously published low-resolution EM map of a SMG1-SMG8-SMG9 complex raises interesting possibility that the nucleotide-binding state of SMG8-SMG9 might impact on the function of the kinase.
NMD, post-transcriptional regulation, C. elegans, crystal twinning
Li, Liang
2017
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Li, Liang (2017): Structural and biochemical charaterization of the C. elegans SMG8-SMG9 core complex. Dissertation, LMU München: Faculty of Chemistry and Pharmacy
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Abstract

Nonsense mediated mRNA decay (NMD) is an important mRNA quality control pathway conserved in eukaryotes. NMD targets aberrant mRNAs carrying premature stop codons (PTCs) for rapid degradation, preventing the accumulation of C-terminally truncated protein products that would otherwise be toxic to cells. NMD involves the concerted action of several trans-acting factors and it is a highly regulated process. A decisive event to trigger NMD in metazoans is the phosphorylation of the RNA helicase UPF1 by the SMG1 kinase. SMG8 and SMG9 form a heterodimer that interacts with SMG1 and inhibits its kinase activity. In recent years, electron microscopy studies of the human SMG1-SMG8-SMG9 complex provided low-resolution structural information that revealed the overall architecture of this complex. Still not much is known about the structure and function of SMG8 and SMG9 and how they interact with each other as well as with SMG1. In this thesis, I used biochemical approaches to identify the core of a SMG8-SMG9 complex amenable to crystallization and determined its three-dimensional structure at the resolution of 2.5 Å. I found that the C. elegans SMG8-SMG9 core complex resembles a G-domain heterodimer with a potentially active subunit (SMG9) and an inactive subunit (SMG8). Following this result, I characterized the nucleotide-binding properties of SMG-SMG9 using biophysical and structural methods. Fitting the atomic model in a previously published low-resolution EM map of a SMG1-SMG8-SMG9 complex raises interesting possibility that the nucleotide-binding state of SMG8-SMG9 might impact on the function of the kinase.