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Ben Ayed I, Jallouli O, Murakami Y, Souissi A, Mallouli S, Bouzid A, Kamoun F, Elloumi I, Frikha F, Tlili A, Weckhuysen S, Kinoshita T, Triki CC, Masmoudi S. Case report: Functional analysis of the p.Arg507Trp variant of the PIGT gene supporting the moderate epilepsy phenotype of mutations in the C-terminal region. Front Neurol 2023; 14:1092887. [PMID: 36970549 PMCID: PMC10034188 DOI: 10.3389/fneur.2023.1092887] [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] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 02/01/2023] [Indexed: 03/29/2023] Open
Abstract
Pathogenic germline variants in the PIGT gene are associated with the "multiple congenital anomalies-hypotonia-seizures syndrome 3" (MCAHS3) phenotype. So far, fifty patients have been reported, most of whom suffer from intractable epilepsy. Recently, a comprehensive analysis of a cohort of 26 patients with PIGT variants has broadened the phenotypical spectrum and indicated that both p.Asn527Ser and p.Val528Met are associated with a milder epilepsy phenotype and less severe outcomes. Since all reported patients are of Caucasian/Polish origin and most harbor the same variant (p.Val528Met), the ability to draw definitive conclusions regarding the genotype-phenotype correlation remains limited. We report a new case with a homozygous variant p.Arg507Trp in the PIGT gene, detected on clinical exome sequencing. The North African patient in question displays a predominantly neurological phenotype with global developmental delay, hypotonia, brain abnormalities, and well-controlled epileptic seizures. Homozygous and heterozygous variants in codon 507 have been reported to cause PIGT deficiency without biochemical confirmation. In this study, FACS analysis of knockout HEK293 cells that had been transfected with wild-type or mutant cDNA constructs demonstrated that the p.Arg507Trp variant leads to mildly reduced activity. Our result confirm the pathogenicity of this variant and strengthen recently reported evidence on the genotype-phenotype correlation of the PIGT variant.
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Affiliation(s)
- Ikhlas Ben Ayed
- Laboratory of Molecular and Cellular Screening Processes (LPCMC), Center of Biotechnology of Sfax, University of Sfax, Sfax, Tunisia
- Medical Genetics Department, University Hedi Chaker Hospital of Sfax, Sfax, Tunisia
| | - Olfa Jallouli
- Child Neurology Department, University Hedi Chaker Hospital of Sfax, Sfax, Tunisia
- Research Laboratory “Neuropédiatrie” LR19ES15, Sfax University, Sfax, Tunisia
| | - Yoshiko Murakami
- Laboratory of Immunoglycobiology, Research Institute for Microbial Diseases, Osaka University, Suita, Japan
| | - Amal Souissi
- Laboratory of Molecular and Cellular Screening Processes (LPCMC), Center of Biotechnology of Sfax, University of Sfax, Sfax, Tunisia
| | - Salma Mallouli
- Child Neurology Department, University Hedi Chaker Hospital of Sfax, Sfax, Tunisia
- Research Laboratory “Neuropédiatrie” LR19ES15, Sfax University, Sfax, Tunisia
| | - Amal Bouzid
- Laboratory of Molecular and Cellular Screening Processes (LPCMC), Center of Biotechnology of Sfax, University of Sfax, Sfax, Tunisia
| | - Fatma Kamoun
- Child Neurology Department, University Hedi Chaker Hospital of Sfax, Sfax, Tunisia
- Research Laboratory “Neuropédiatrie” LR19ES15, Sfax University, Sfax, Tunisia
| | - Ines Elloumi
- Laboratory of Molecular and Cellular Screening Processes (LPCMC), Center of Biotechnology of Sfax, University of Sfax, Sfax, Tunisia
| | - Fakher Frikha
- Laboratory of Molecular and Cellular Screening Processes (LPCMC), Center of Biotechnology of Sfax, University of Sfax, Sfax, Tunisia
| | - Abdelaziz Tlili
- Department of Applied Biology, College of Sciences, University of Sharjah, Sharjah, United Arab Emirates
- Human Genetics and Stem Cell Laboratory, Research Institute of Sciences and Engineering, University of Sharjah, Sharjah, United Arab Emirates
| | | | - Taroh Kinoshita
- Laboratory of Immunoglycobiology, Research Institute for Microbial Diseases, Osaka University, Suita, Japan
- Center for Infectious Disease Education and Research, Osaka University, Suita, Japan
| | - Chahnez Charfi Triki
- Child Neurology Department, University Hedi Chaker Hospital of Sfax, Sfax, Tunisia
- Research Laboratory “Neuropédiatrie” LR19ES15, Sfax University, Sfax, Tunisia
| | - Saber Masmoudi
- Laboratory of Molecular and Cellular Screening Processes (LPCMC), Center of Biotechnology of Sfax, University of Sfax, Sfax, Tunisia
- *Correspondence: Saber Masmoudi
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Sah SK, Shefali S, Yadav A, Som P, Komath SS. The caspase-like Gpi8 subunit of Candida albicans GPI transamidase is a metal-dependent endopeptidase. Biochem Biophys Res Commun 2020; 525:S0006-291X(20)30268-0. [PMID: 32081427 DOI: 10.1016/j.bbrc.2020.02.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 02/03/2020] [Indexed: 10/25/2022]
Abstract
GPI anchored proteins (GPI-APs) act at the frontiers of cells, decoding environmental cues and determining host-pathogen interactions in several lower eukaryotes. They are also essential for viability in lower eukaryotes. The GPI biosynthetic pathway begins at the ER and follows a roughly linear pathway to generate the complete precursor (CP) glycolipid. The GPI transamidase (GPIT) transfers this glycolipid to the C-terminal end of newly translated proteins after removing their GPI attachment signal sequence (SS). The GPIT subunit that cleaves SS is Gpi8, a protein with a conserved Cys/His catalytic dyad typical of cysteine proteases. A CaGPI8 heterozygous mutant accumulates CPs and has reduced cell surface GPI-APs. Using a simple cell-free assay, we demonstrate that the heterozygous CaGPI8 strain has low endopeptidase activity as well. The revertant strain is restored in all these phenotypes. CaGpi8 is also shown to be a metalloenzyme, whose protease activity is sensitive to agents that modify Cys/His residues.
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Affiliation(s)
- Sudisht Kumar Sah
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Shailja Shefali
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Anshuman Yadav
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Punnag Som
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.
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Wang Y, Hirata T, Maeda Y, Murakami Y, Fujita M, Kinoshita T. Free, unlinked glycosylphosphatidylinositols on mammalian cell surfaces revisited. J Biol Chem 2019; 294:5038-5049. [PMID: 30728244 DOI: 10.1074/jbc.ra119.007472] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 01/30/2019] [Indexed: 12/17/2022] Open
Abstract
Glycosylphosphatidylinositols (GPIs) are linked to many cell-surface proteins, anchor these proteins in the membrane, and are well characterized. However, GPIs that exist in the free form on the mammalian cell surface remain largely unexplored. To investigate free GPIs in cultured cell lines and mouse tissues, here we used the T5-4E10 mAb (T5 mAb), which recognizes unlinked GPIs having an N-acetylgalactosamine (GalNAc) side chain linked to the first mannose at the nonreducing terminus. We detected free GPIs bearing the GalNAc side chain on the surface of Neuro2a and CHO, but not of HEK293, K562, and C2C12 cells. Furthermore, free GPIs were present in mouse pons, medulla oblongata, spinal cord, testis, epididymis, and kidney. Using a panel of Chinese hamster ovary cells defective in both GPI-transamidase and GPI remodeling pathway, we demonstrate that free GPIs follow the same structural remodeling pathway during passage from the endoplasmic reticulum to the plasma membrane as do protein-linked GPI. Specifically, free GPIs underwent post-GPI attachment to protein 1 (PGAP1)-mediated inositol deacylation, PGAP5-mediated removal of the ethanolamine phosphate from the second mannose, and PGAP3- and PGAP2-mediated fatty acid remodeling. Moreover, T5 mAb recognized free GPIs even if the inositol-linked acyl chain or ethanolamine-phosphate side chain linked to the second mannose is not removed. In contrast, addition of a fourth mannose by phosphatidylinositol glycan anchor biosynthesis class Z (PIGZ) inhibited T5 mAb-mediated detection of free GPIs. Our results indicate that free GPIs are normal components of the plasma membrane in some tissues and further characterize free GPIs in mammalian cells.
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Affiliation(s)
- Yicheng Wang
- From the Research Institute for Microbial Diseases and.,World Premier International (WPI) Immunology Frontier Research Center, Osaka University, Suita, Osaka 565-0871, Japan and
| | | | - Yusuke Maeda
- From the Research Institute for Microbial Diseases and
| | - Yoshiko Murakami
- From the Research Institute for Microbial Diseases and.,World Premier International (WPI) Immunology Frontier Research Center, Osaka University, Suita, Osaka 565-0871, Japan and
| | - Morihisa Fujita
- the Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, Jiangsu 214122, China
| | - Taroh Kinoshita
- From the Research Institute for Microbial Diseases and .,World Premier International (WPI) Immunology Frontier Research Center, Osaka University, Suita, Osaka 565-0871, Japan and
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Eisenhaber B, Eisenhaber S, Kwang TY, Grüber G, Eisenhaber F. Transamidase subunit GAA1/GPAA1 is a M28 family metallo-peptide-synthetase that catalyzes the peptide bond formation between the substrate protein's omega-site and the GPI lipid anchor's phosphoethanolamine. Cell Cycle 2014; 13:1912-7. [PMID: 24743167 PMCID: PMC4111754 DOI: 10.4161/cc.28761] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The transamidase subunit GAA1/GPAA1 is predicted to be the enzyme that catalyzes the attachment of the glycosylphosphatidyl (GPI) lipid anchor to the carbonyl intermediate of the substrate protein at the ω-site. Its ~300-amino acid residue lumenal domain is a M28 family metallo-peptide-synthetase with an α/β hydrolase fold, including a central 8-strand β-sheet and a single metal (most likely zinc) ion coordinated by 3 conserved polar residues. Phosphoethanolamine is used as an adaptor to make the non-peptide GPI lipid anchor look chemically similar to the N terminus of a peptide.
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Affiliation(s)
- Birgit Eisenhaber
- Bioinformatics Institute (BII); A*STAR; Singapore, Republic of Singapore
| | - Stephan Eisenhaber
- Department of Physical Chemistry; University of Vienna; Wien/Vienna, Republic of Austria
| | - Toh Yew Kwang
- Bioinformatics Institute (BII); A*STAR; Singapore, Republic of Singapore
| | - Gerhard Grüber
- Bioinformatics Institute (BII); A*STAR; Singapore, Republic of Singapore; Nanyang Technological University; School of Biological Sciences; Singapore, Republic of Singapore
| | - Frank Eisenhaber
- Bioinformatics Institute (BII); A*STAR; Singapore, Republic of Singapore; Department of Biological Sciences (DBS); National University of Singapore (NUS); Singapore, Republic of Singapore; School of Computer Engineering (SCE); Nanyang Technological University (NTU); Singapore, Republic of Singapore
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