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Katirci E, Kirimlioglu E, Oflamaz AO, Hidisoglu E, Cernomorcenco A, Yargıcoğlu P, Ozen S, Demir N. Expression levels of tam receptors and ligands in the testes of rats exposed to short and middle-term 2100 MHz radiofrequency radiation. Bioelectromagnetics 2024; 45:235-248. [PMID: 38725116 DOI: 10.1002/bem.22504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 03/25/2024] [Accepted: 03/30/2024] [Indexed: 06/18/2024]
Abstract
With advances in technology, the emission of radiofrequency radiation (RFR) into the environment, particularly from mobile devices, has become a growing concern. Tyro 3, Axl, and Mer (TAM) receptors and their ligands are essential for spermatogenesis and testosterone production. RFR has been shown to induce testicular cell apoptosis by causing inflammation and disrupting homeostasis. This study aimed to investigate the role of TAM receptors and ligands in the maintenance of homeostasis and elimination of apoptotic cells in the testes (weeks), short-term sham exposure (sham/1 week), and middle-term sham exposure (sham/10 weeks). Testicular morphology was assessed using hematoxylin-eosin staining, while immunohistochemical staining was performed to assess expression levels of TAM receptors and ligands in the testes of all groups. The results showed that testicular morphology was normal in the control, sham/1 week, and sham/10 weeks groups. However, abnormal processes of spermatogenesis and seminiferous tubule morphology were observed in RFR exposure groups. Cleaved Caspase 3 immunoreactivity showed statistically significant difference in 1 and 10 weeks exposure groups compared to control group. Moreover, there was no significant difference in the immunoreactivity of Tyro 3, Axl, Mer, Gas 6, and Pros 1 between groups. Moreover, Tyro 3 expression in Sertoli cells was statistically significantly increased in RFR exposure groups compared to the control. Taken together, the results suggest that RFR exposure negatively affects TAM signalling, preventing the clearance of apoptotic cells, and this process may lead to infection and inflammation. As a result, rat testicular morphology and function may be impaired.
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Affiliation(s)
- Ertan Katirci
- Department of Histology and Embryology, Akdeniz University Faculty of Medicine, Antalya, Turkey
| | - Esma Kirimlioglu
- Department of Histology and Embryology, Akdeniz University Faculty of Medicine, Antalya, Turkey
| | - Asli O Oflamaz
- Department of Histology and Embryology, Akdeniz University Faculty of Medicine, Antalya, Turkey
| | - Enis Hidisoglu
- Department of Biophysics, Akdeniz University Faculty of Medicine, Antalya, Turkey
- Department of Biophysics, Faculty of Medicine, Izmir Bakircay University, Izmir, Turkey
- Department of Drug Science and Technology, Universityof Turin, Turin, Italy
| | - Alexandra Cernomorcenco
- Department of Histology and Embryology, Akdeniz University Faculty of Medicine, Antalya, Turkey
| | - Piraye Yargıcoğlu
- Department of Biophysics, Akdeniz University Faculty of Medicine, Antalya, Turkey
| | - Sukru Ozen
- Department of Electrical and Electronics Engineering, Akdeniz University Faculty of Engineering, Antalya, Turkey
| | - Necdet Demir
- Department of Histology and Embryology, Akdeniz University Faculty of Medicine, Antalya, Turkey
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Sakuragi T, Kanai R, Otani M, Kikkawa M, Toyoshima C, Nagata S. The role of the C-terminal tail region as a plug to regulate XKR8 lipid scramblase. J Biol Chem 2024; 300:105755. [PMID: 38364890 PMCID: PMC10938166 DOI: 10.1016/j.jbc.2024.105755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 01/27/2024] [Accepted: 02/10/2024] [Indexed: 02/18/2024] Open
Abstract
XK-related 8 (XKR8), in complex with the transmembrane glycoprotein basigin, functions as a phospholipid scramblase activated by the caspase-mediated cleavage or phosphorylation of its C-terminal tail. It carries a putative phospholipid translocation path of multiple hydrophobic and charged residues in the transmembrane region. It also has a crucial tryptophan at the exoplasmic end of the path that regulates its scrambling activity. We herein investigated the tertiary structure of the human XKR8-basigin complex embedded in lipid nanodiscs at an overall resolution of 3.66 Å. We found that the C-terminal tail engaged in intricate polar and van der Waals interactions with a groove at the cytoplasmic surface of XKR8. These interactions maintained the inactive state of XKR8. Point mutations to disrupt these interactions strongly enhanced the scrambling activity of XKR8, suggesting that the activation of XKR8 is mediated by releasing the C-terminal tail from the cytoplasmic groove. We speculate that the cytoplasmic tail region of XKR8 functions as a plug to prevent the scrambling of phospholipids.
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Affiliation(s)
- Takaharu Sakuragi
- Laboratory of Biochemistry and Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan
| | - Ryuta Kanai
- Institute for Quantitative Biosciences, The University of Tokyo, Tokyo, Japan
| | - Mayumi Otani
- Laboratory of Biochemistry and Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan
| | - Masahide Kikkawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Chikashi Toyoshima
- Institute for Quantitative Biosciences, The University of Tokyo, Tokyo, Japan
| | - Shigekazu Nagata
- Laboratory of Biochemistry and Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan.
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He SF, Han WC, Shao YY, Zhang HB, Hong WX, Yang QH, Zhang YQ, He RR, Sun J. Iridium(III) complex induces apoptosis in HeLa cells by regulating mitochondrial and PI3K/AKT signaling pathways: In vitro and in vivo experiments. Bioorg Chem 2023; 141:106867. [PMID: 37734195 DOI: 10.1016/j.bioorg.2023.106867] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 09/08/2023] [Accepted: 09/14/2023] [Indexed: 09/23/2023]
Abstract
Cyclometalated iridium complexes with mitochondrial targeting show great potential as substitutes for platinum-based complexes because of their strong anti-cancer properties. Three novel cyclometalated iridium(III) compounds were synthesized and evaluated in five different cell lines as part of the ongoing systematic investigations of these compounds. The complexes were prepared using 4,7-dichloro-1,10-phenanthroline ligands. The cytotoxicity of complexes Ir1-Ir3 towards HeLa cells was shown to be high, with IC50 values of 0.83±0.06, 4.73±0.11, and 4.95±0.62 μM, respectively. Complex Ir1 could be ingested by HeLa cells in 3 h and has shown high selectivity toward mitochondria. Subsequent investigations demonstrated that Ir1 triggered apoptosis in HeLa cells by augmenting the generation of reactive oxygen species (ROS), reducing the mitochondrial membrane potential, and depleting ATP levels. Furthermore, the movement of cells was significantly suppressed and the progression of the cell cycle was arrested in the G0/G1 phase following the administration of Ir1. The Western blot analysis demonstrated that the induction of apoptosis in HeLa cells by Ir1 involves the activation of the mitochondria-dependent channel and the PI3K/AKT signaling pathway. No significant cytotoxicity was observed in zebrafish embryos at concentrations less than or equal to 16 µM, e.g., survival rate and developmental abnormalities. In vivo, antitumor assay demonstrated that Ir1 suppressed tumor growth in mice. Therefore, our work shows that complex Ir1 could be a promising candidate for developing novel antitumor drugs.
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Affiliation(s)
- Shu-Fen He
- Department of Pharmacy, The Tenth Affiliated Hospital of Southern Medical University (Dongguan People's Hospital), Dongguan 523059, China
| | - Wei-Chao Han
- Department of Pharmacy, The Tenth Affiliated Hospital of Southern Medical University (Dongguan People's Hospital), Dongguan 523059, China
| | - Ying-Ying Shao
- Department of Pharmacy, The Tenth Affiliated Hospital of Southern Medical University (Dongguan People's Hospital), Dongguan 523059, China
| | - Han-Bin Zhang
- Department of Pharmacy, The Tenth Affiliated Hospital of Southern Medical University (Dongguan People's Hospital), Dongguan 523059, China
| | - Wen-Xin Hong
- Department of Health, Dongguan Maternal and Child Health Care Hospital, Dongguan 523129, China
| | - Qiu-Hong Yang
- Department of Pharmacy, The Tenth Affiliated Hospital of Southern Medical University (Dongguan People's Hospital), Dongguan 523059, China
| | - Yu-Qing Zhang
- School of Pharmacy, Guangdong Medical University, Dongguan 523808, China
| | - Rui-Rong He
- Department of Pharmacy, The Tenth Affiliated Hospital of Southern Medical University (Dongguan People's Hospital), Dongguan 523059, China.
| | - Jing Sun
- School of Pharmacy, Guangdong Medical University, Dongguan 523808, China.
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Sakuragi T, Nagata S. Regulation of phospholipid distribution in the lipid bilayer by flippases and scramblases. Nat Rev Mol Cell Biol 2023:10.1038/s41580-023-00604-z. [PMID: 37106071 PMCID: PMC10134735 DOI: 10.1038/s41580-023-00604-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/09/2023] [Indexed: 04/29/2023]
Abstract
Cellular membranes function as permeability barriers that separate cells from the external environment or partition cells into distinct compartments. These membranes are lipid bilayers composed of glycerophospholipids, sphingolipids and cholesterol, in which proteins are embedded. Glycerophospholipids and sphingolipids freely move laterally, whereas transverse movement between lipid bilayers is limited. Phospholipids are asymmetrically distributed between membrane leaflets but change their location in biological processes, serving as signalling molecules or enzyme activators. Designated proteins - flippases and scramblases - mediate this lipid movement between the bilayers. Flippases mediate the confined localization of specific phospholipids (phosphatidylserine (PtdSer) and phosphatidylethanolamine) to the cytoplasmic leaflet. Scramblases randomly scramble phospholipids between leaflets and facilitate the exposure of PtdSer on the cell surface, which serves as an important signalling molecule and as an 'eat me' signal for phagocytes. Defects in flippases and scramblases cause various human diseases. We herein review the recent research on the structure of flippases and scramblases and their physiological roles. Although still poorly understood, we address the mechanisms by which they translocate phospholipids between lipid bilayers and how defects cause human diseases.
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Affiliation(s)
- Takaharu Sakuragi
- Biochemistry & Immunology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Shigekazu Nagata
- Biochemistry & Immunology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan.
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Chen K, Li C, Dong C, Cen X, Wang Y, Liang Y, Zhu Y, Fang S, Jiang H. A dominant variant in apoptosis-related gene XKR8 is relevant to hereditary auditory neuropathy. J Transl Med 2023; 21:279. [PMID: 37101210 PMCID: PMC10131414 DOI: 10.1186/s12967-023-04139-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 04/16/2023] [Indexed: 04/28/2023] Open
Abstract
BACKGROUND Auditory neuropathy is an unusual type of hearing loss. At least 40% of patients with this disease have underlying genetic causes. However, in many hereditary auditory neuropathy cases, etiology remains undetermined. METHODS We collected data and blood samples from a four-generation Chinese family. After excluding relevant variants in known deafness-related genes, exome sequencing was conducted. Candidate genes were verified by pedigree segregation, transcript/protein expression in the mouse cochlea, and plasmid expression studies in HEK 293T cells. Moreover, a mutant mouse model was generated and underwent hearing evaluations; protein localization in the inner ear was also assessed. RESULTS The clinical features of the family were diagnosed as auditory neuropathy. A novel variant c.710G > A (p.W237X) in apoptosis-related gene XKR8 was identified. Genotyping of 16 family members confirmed the segregation of this variant with the deafness phenotype. Both XKR8 mRNA and XKR8 protein were expressed in the mouse inner ear, predominantly in regions of spiral ganglion neurons; Moreover, this nonsense variant impaired the surface localization of XKR8 in cells. Transgenic mutant mice exhibited late-onset auditory neuropathy, and their altered XKR8 protein localization in the inner ear confirmed the damaging effects of this variant. CONCLUSIONS We identified a variant in the XKR8 gene that is relevant to auditory neuropathy. The essential role of XKR8 in inner ear development and neural homeostasis should be explored.
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Affiliation(s)
- Kaitian Chen
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
| | - Changwu Li
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Department of Otorhinolaryngology, Hainan General Hospital, Haikou, 570311, Hainan, China
| | - Chang Dong
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Department of Otorhinolaryngology, Hainan General Hospital, Haikou, 570311, Hainan, China
| | - Xiaoqing Cen
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
| | - Yueying Wang
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
| | - Yue Liang
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
| | - Yuanping Zhu
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Department of Otorhinolaryngology, Hainan General Hospital, Haikou, 570311, Hainan, China
| | - Shubin Fang
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China
| | - Hongyan Jiang
- Department of Otorhinolaryngology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China.
- Institute of Otorhinolaryngology, Sun Yat-sen University, Guangzhou, 510080, Guangdong, People's Republic of China.
- Department of Otorhinolaryngology, Hainan General Hospital, Haikou, 570311, Hainan, China.
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Shi J, Gao S, Chen Z, Chen Z, Yun D, Wu X, Sun F. Absence of MerTK disrupts spermatogenesis in an age-dependent manner. Mol Cell Endocrinol 2023; 560:111815. [PMID: 36379275 DOI: 10.1016/j.mce.2022.111815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 11/02/2022] [Accepted: 11/06/2022] [Indexed: 11/15/2022]
Abstract
Spermatogenesis is a highly specialized cell differentiation process regulated by the testicular microenvironment. During the process of spermatogenesis, phagocytosis performs an essential role in male germ cell development, and its dysfunction in the testis can cause reproduction defects. MerTK, as a critical protein of phagocytosis, facilitates the removal of apoptotic substrates from the retina and ovaries through cooperation with several phagocytosis receptors. However, its role in mammalian spermatogenesis remains undefined. Here, we found that 30-week-old MerTK-/- male mice developed oligoasthenospermia due to abnormal spermatogenesis. These mice showed damaged seminiferous tubule structure, as well as altered spermatogonia proliferation and differentiation. We also found that Sertoli cells from MerTK-/- mice had decreased phagocytic activity on apoptotic germ cells in vitro. Moreover, a transcriptomic analysis demonstrated that the pivotal genes involved in spermatid differentiation and development changed expression. These results indicate that MerTK is crucial for spermatogenesis, as it regulates the crosstalk between germ cells and Sertoli cells. This provides us insight into the molecular mechanism of MerTK on spermatogenesis and its implications for the diagnosis and treatment of human male infertility.
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Affiliation(s)
- Jie Shi
- Institute of Reproductive Medicine, Medical School of Nantong University, Nantong, 226001, China
| | - Sheng Gao
- Institute of Reproductive Medicine, Medical School of Nantong University, Nantong, 226001, China
| | - Zhengru Chen
- Institute of Reproductive Medicine, Medical School of Nantong University, Nantong, 226001, China
| | - Zifeng Chen
- Institute of Reproductive Medicine, Medical School of Nantong University, Nantong, 226001, China
| | - Damin Yun
- Institute of Reproductive Medicine, Medical School of Nantong University, Nantong, 226001, China
| | - Xiaolong Wu
- Department of Urology & Andrology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310016, China
| | - Fei Sun
- Institute of Reproductive Medicine, Medical School of Nantong University, Nantong, 226001, China.
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Tang D, Wang Y, Dong X, Yuan Y, Kang F, Tian W, Wang K, Li H, Qi S. Scramblases and virus infection. Bioessays 2022; 44:e2100261. [DOI: 10.1002/bies.202100261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 11/06/2022]
Affiliation(s)
- Dan Tang
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Yichang Wang
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Xiuju Dong
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Yiqiong Yuan
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Fanchen Kang
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Weidong Tian
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Kunjie Wang
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Hong Li
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
| | - Shiqian Qi
- Department of Urology Institute of Urology (Laboratory of Reconstructive Urology) State Key Laboratory of Oral Disease West China Hospital of Stomatology West China Hospital Sichuan University Chengdu Sichuan China
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Connexin43 represents an important regulator for Sertoli cell morphology, Sertoli cell nuclear ultrastructure, and Sertoli cell maturation. Sci Rep 2022; 12:12898. [PMID: 35902708 PMCID: PMC9334284 DOI: 10.1038/s41598-022-16919-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 07/18/2022] [Indexed: 11/23/2022] Open
Abstract
The Sertoli cell (SC)-specific knockout (KO) of connexin43 (Cx43) was shown to be an effector of multiple histological changes in tubular morphology, resulting in germ cell loss through to a Sertoli-cell-only (SCO) phenotype and vacuolated seminiferous tubules containing SC-clusters. Our present study focused on the effects of Cx43 loss on SC ultrastructure. Using serial block-face scanning electron microscopy (SBF-SEM), we could confirm previous results. Ultrastructural analysis of Sertoli cell nuclei (SCN) revealed that these appear in clusters with a phenotype resembling immature/proliferating SCs in KO mice. Surprisingly, SCs of fertile wild type (WT) mice contained SCN with a predominantly smooth surface instead of deep indentations of the nuclear envelope, suggesting that these indentations do not correlate with germ cell support or spermatogenesis. SBF-SEM facilitated the precise examination of clustered SCs. Even if the exact maturation state of mutant SCs remained unclear, our study could detect indications of cellular senescence as well as immaturity, emphasising that Cx43 affects SC maturation. Moreover, Sudan III staining and transmission electron microscopy (TEM) demonstrated an altered lipid metabolism in SCs of Cx43 deficient mice.
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Acciani MD, Brindley MA. Scrambled or flipped: 5 facts about how cellular phosphatidylserine localization can mediate viral replication. PLoS Pathog 2022; 18:e1010352. [PMID: 35245334 PMCID: PMC8896693 DOI: 10.1371/journal.ppat.1010352] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Affiliation(s)
- Marissa Danielle Acciani
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, Georgia, United States of America
| | - Melinda Ann Brindley
- Department of Infectious Diseases, Department of Population Health, College of Veterinary Medicine, University of Georgia, Athens, Georgia, United States of America
- * E-mail:
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The tertiary structure of the human Xkr8-Basigin complex that scrambles phospholipids at plasma membranes. Nat Struct Mol Biol 2021; 28:825-834. [PMID: 34625749 PMCID: PMC8500837 DOI: 10.1038/s41594-021-00665-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 08/19/2021] [Indexed: 02/04/2023]
Abstract
Xkr8-Basigin is a plasma membrane phospholipid scramblase activated by kinases or caspases. We combined cryo-EM and X-ray crystallography to investigate its structure at an overall resolution of 3.8 Å. Its membrane-spanning region carrying 22 charged amino acids adopts a cuboid-like structure stabilized by salt bridges between hydrophilic residues in transmembrane helices. Phosphatidylcholine binding was observed in a hydrophobic cleft on the surface exposed to the outer leaflet of the plasma membrane. Six charged residues placed from top to bottom inside the molecule were essential for scrambling phospholipids in inward and outward directions, apparently providing a pathway for their translocation. A tryptophan residue was present between the head group of phosphatidylcholine and the extracellular end of the path. Its mutation to alanine made the Xkr8-Basigin complex constitutively active, indicating that it plays a vital role in regulating its scramblase activity. The structure of Xkr8-Basigin provides insights into the molecular mechanisms underlying phospholipid scrambling.
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