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Abreo TJ, Thompson EC, Madabushi A, Soh H, Varghese N, Vanoye CG, Springer K, Park KL, Johnson J, Sims S, Ji Z, Chavez AG, Jankovic MJ, Habte B, Zuberi A, Lutz C, Wang Z, Krishnan V, Dudler L, Einsele-Scholz S, Noebels JL, George AL, Maheshwari A, Tzingounis AV, Cooper EC. Plural molecular and cellular mechanisms of pore domain KCNQ2 encephalopathy. bioRxiv 2024:2024.01.04.574177. [PMID: 38260608 PMCID: PMC10802467 DOI: 10.1101/2024.01.04.574177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
KCNQ2 variants in children with neurodevelopmental impairment are difficult to assess due to their heterogeneity and unclear pathogenic mechanisms. We describe a child with neonatal-onset epilepsy, developmental impairment of intermediate severity, and KCNQ2 G256W heterozygosity. Analyzing prior KCNQ2 channel cryoelectron microscopy models revealed G256 as keystone of an arch-shaped non-covalent bond network linking S5, the pore turret, and the ion path. Co-expression with G256W dominantly suppressed conduction by wild-type subunits in heterologous cells. Ezogabine partly reversed this suppression. G256W/+ mice have epilepsy leading to premature deaths. Hippocampal CA1 pyramidal cells from G256W/+ brain slices showed hyperexcitability. G256W/+ pyramidal cell KCNQ2 and KCNQ3 immunolabeling was significantly shifted from axon initial segments to neuronal somata. Despite normal mRNA levels, G256W/+ mouse KCNQ2 protein levels were reduced by about 50%. Our findings indicate that G256W pathogenicity results from multiplicative effects, including reductions in intrinsic conduction, subcellular targeting, and protein stability. These studies reveal pore "turret arch" bonding as a KCNQ structural novelty and introduce a valid animal model of KCNQ2 encephalopathy. Our results, spanning structure to behavior, may be broadly applicable because the majority of KCNQ2 encephalopathy patients share variants near the selectivity filter.
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Affiliation(s)
- Timothy J Abreo
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Emma C Thompson
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
| | - Anuraag Madabushi
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
| | - Heun Soh
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA
| | - Nissi Varghese
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA
| | - Carlos G Vanoye
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Kristen Springer
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT, USA
| | - Kristen L Park
- Department of Pediatrics, Childrens Colorado, University of Colorado, Aurora, CO, USA
- Department of Neurology, Childrens Colorado, University of Colorado, Aurora, CO, USA
| | | | | | - Zhigang Ji
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
| | - Ana G Chavez
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | | | - Bereket Habte
- Department of Pediatrics, Childrens Colorado, University of Colorado, Aurora, CO, USA
- Department of Neurology, Childrens Colorado, University of Colorado, Aurora, CO, USA
| | - Aamir Zuberi
- The Rare Disease Translational Center, Jackson Laboratory, Bar Harbor, ME, USA
| | - Cathleen Lutz
- The Rare Disease Translational Center, Jackson Laboratory, Bar Harbor, ME, USA
| | - Zhao Wang
- Department of Biochemistry and Molecular Pharmacology, Baylor College of Medicine, Houston, TX, USA
- CryoEM Core, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Vaishnav Krishnan
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
- Department of Psychiatry and Behavioral Sciences, Baylor College of Medicine, Houston, TX, USA
| | - Lisa Dudler
- Center for Human Genetics Tübingen, Tübingen, Germany
| | | | - Jeffrey L Noebels
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Alfred L George
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Atul Maheshwari
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | | | - Edward C Cooper
- Department of Neurology, Baylor College of Medicine, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
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Varshney U, Ramesh V, Madabushi A, Gaur R, Subramanya HS, RajBhandary UL. Mycobacterium tuberculosis Rv2118c codes for a single-component homotetrameric m1A58 tRNA methyltransferase. Nucleic Acids Res 2004; 32:1018-27. [PMID: 14960715 PMCID: PMC373377 DOI: 10.1093/nar/gkh207] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Modified nucleosides in tRNAs play important roles in tRNA structure, biosynthesis and function, and serve as crucial determinants of bacterial growth and virulence. In the yeast Saccharomyces cerevisiae, mutants defective in N1-methylation of a highly conserved adenosine (A58) in the TPsiC loop of initiator tRNA are non-viable. The yeast m1A58 methyltransferase is a heterotetramer consisting of two different polypeptide chains, Gcd14p and Gcd10p. Interestingly, while m1A58 is not found in most eubacteria, the mycobacterial tRNAs have m1A58. Here, we report on the cloning, overexpression, purification and biochemical characterization of the Rv2118c gene-encoded protein (Rv2118p) from Mycobacterium tuberculosis, which is homologous to yeast Gcd14p. We show that Rv2118c codes for a protein of approximately 31 kDa. Activity assays, modified base analysis and primer extension experiments using reverse transcriptase reveal that Rv2118p is an S-adenosyl-l-methionine-dependent methyltransferase which carries out m1A58 modification in tRNAs, both in vivo and in vitro. Remarkably, when expressed in Escherichia coli, the enzyme methylates the endogenous E.coli initiator tRNA essentially quantitatively. Furthermore, unlike its eukaryotic counterpart, which is a heterotetramer, the mycobacterial enzyme is a homotetramer. Also, the presence of rT modification at position 54, which was found to inhibit the Tetrahymena pyriformis enzyme, does not affect the activity of Rv2118p. Thus, the mycobacterial m1A58 tRNA methyltransferase possesses distinct biochemical properties. We discuss aspects of the biological relevance of Rv2118p in M.tuberculosis, and its potential use as a drug target to control the growth of mycobacteria.
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Affiliation(s)
- U Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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