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Jones AG, Aquilino M, Tinker RJ, Duncan L, Jenkins Z, Carvill GL, DeWard SJ, Grange DK, Hajianpour MJ, Halliday BJ, Holder-Espinasse M, Horvath J, Maitz S, Nigro V, Morleo M, Paul V, Spencer C, Esterhuizen AI, Polster T, Spano A, Gómez-Lozano I, Kumar A, Poke G, Phillips JA, Underhill HR, Gimenez G, Namba T, Robertson SP. Clustered de novo start-loss variants in GLUL result in a developmental and epileptic encephalopathy via stabilization of glutamine synthetase. Am J Hum Genet 2024; 111:729-741. [PMID: 38579670 PMCID: PMC11023914 DOI: 10.1016/j.ajhg.2024.03.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 03/05/2024] [Accepted: 03/06/2024] [Indexed: 04/07/2024] Open
Abstract
Glutamine synthetase (GS), encoded by GLUL, catalyzes the conversion of glutamate to glutamine. GS is pivotal for the generation of the neurotransmitters glutamate and gamma-aminobutyric acid and is the primary mechanism of ammonia detoxification in the brain. GS levels are regulated post-translationally by an N-terminal degron that enables the ubiquitin-mediated degradation of GS in a glutamine-induced manner. GS deficiency in humans is known to lead to neurological defects and death in infancy, yet how dysregulation of the degron-mediated control of GS levels might affect neurodevelopment is unknown. We ascertained nine individuals with severe developmental delay, seizures, and white matter abnormalities but normal plasma and cerebrospinal fluid biochemistry with de novo variants in GLUL. Seven out of nine were start-loss variants and two out of nine disrupted 5' UTR splicing resulting in splice exclusion of the initiation codon. Using transfection-based expression systems and mass spectrometry, these variants were shown to lead to translation initiation of GS from methionine 18, downstream of the N-terminal degron motif, resulting in a protein that is stable and enzymatically competent but insensitive to negative feedback by glutamine. Analysis of human single-cell transcriptomes demonstrated that GLUL is widely expressed in neuro- and glial-progenitor cells and mature astrocytes but not in post-mitotic neurons. One individual with a start-loss GLUL variant demonstrated periventricular nodular heterotopia, a neuronal migration disorder, yet overexpression of stabilized GS in mice using in utero electroporation demonstrated no migratory deficits. These findings underline the importance of tight regulation of glutamine metabolism during neurodevelopment in humans.
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Affiliation(s)
- Amy G Jones
- Department of Women's and Children's Health, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | - Matilde Aquilino
- Neuroscience Center, HiLIFE - Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland
| | - Rory J Tinker
- Vanderbilt University Medical Center, Nashville, TN, USA
| | - Laura Duncan
- Center for Individualized Medicine, Mayo Clinic, Jacksonville, FL, USA
| | - Zandra Jenkins
- Department of Women's and Children's Health, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | - Gemma L Carvill
- Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | | | | | | | - Benjamin J Halliday
- Department of Women's and Children's Health, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | | | | | - Silvia Maitz
- Medical Genetics Service, Oncology Department of Southern Switzerland, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Vincenzo Nigro
- Department of Precision Medicine, University of Campania "Luigi Vanvitelli," Naples, Italy
| | - Manuela Morleo
- Department of Precision Medicine, University of Campania "Luigi Vanvitelli," Naples, Italy
| | | | - Careni Spencer
- Division of Human Genetics, Department of Pathology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa; Department of Medicine, Division of Human Genetics, Groote Schuur Hospital, Cape Town, South Africa
| | - Alina I Esterhuizen
- Division of Human Genetics, Department of Pathology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa; Neuroscience Institute, University of Cape Town, Cape Town, South Africa; National Health Laboratory Service, Groote Schuur Hospital, Cape Town, South Africa
| | - Tilman Polster
- Department of Epileptology (Krankenhaus Mara, Bethel Epilepsy Center) Medical School OWL, Bielefeld University, Bielefeld, Germany
| | - Alice Spano
- Maggiore Della Carità Hospital, Novara, Italy
| | - Inés Gómez-Lozano
- Neuroscience Center, HiLIFE - Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland
| | - Abhishek Kumar
- Centre for Protein Research, University of Otago, Dunedin, New Zealand
| | - Gemma Poke
- Genetics Health Service New Zealand, Wellington Hospital, Wellington, New Zealand
| | | | | | - Gregory Gimenez
- Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | - Takashi Namba
- Neuroscience Center, HiLIFE - Helsinki Institute of Life Science, University of Helsinki, Helsinki, Finland
| | - Stephen P Robertson
- Department of Women's and Children's Health, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand.
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Acevedo LA, Kwon J, Nicholson LK. Quantification of reaction cycle parameters for an essential molecular switch in an auxin-responsive transcription circuit in rice. Proc Natl Acad Sci U S A 2019; 116:2589-94. [PMID: 30696765 DOI: 10.1073/pnas.1817038116] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Protein-based molecular switches play critical roles in biological processes. The importance of the prolyl cis-trans switch is underscored by the ubiquitous presence of peptidyl prolyl isomerases such as cyclophilins that accelerate the intrinsically slow isomerization rate. In rice, a tryptophan-proline (W-P) cis-trans switch in transcription repressor protein OsIAA11 along with its associated cyclophilin LRT2 are essential components in a negative feedback gene regulation circuit that controls lateral root initiation in response to the plant hormone auxin. Importantly, no quantitative characterizations of the individual (microscopic) thermodynamic and kinetic parameters for any cyclophilin-catalyzed W-P isomerization have been reported. Here we present NMR studies that determine and independently validate these parameters for LRT2 catalysis of the W-P motif in OsIAA11, providing predictive power for understanding the role of this switch in the auxin-responsive circuit and the resulting lateral rootless phenotype in rice. We show that the observed isomerization rate is linearly dependent on LRT2 concentration but is independent of OsIAA11 concentration over a wide range, and LRT2 is optimally tuned to maintain OsIAA11 at its cis-trans equilibrium to supply the slower downstream cis-specific proteasomal degradation with maximal OsIAA11 substrate. This indicates that accelerating the LRT2-catalyzed isomerization would not accelerate OsIAA degradation, whereas decreasing this rate via targeted mutation could reveal relationships between circuit dynamics and lateral root development. Moreover, we show that sequences flanking the highly conserved Aux/IAA W-P motif do not impact LRT2 catalysis, suggesting that the parameters determined here are broadly applicable across highly conserved cyclophilins and their Aux/IAA targets.
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