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Alkahtani S, Alkahtane AA, Alarifi S. Physiological and Pathogenesis Significance of Chorein in Health and Disease. Physiol Res 2024; 73:189-203. [PMID: 38710051 PMCID: PMC11081191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 11/30/2023] [Indexed: 05/08/2024] Open
Abstract
This comprehensive review explores the physiological and pathophysiological significance of VPS13A, a protein encoded by the VPS13A gene. The VPS13A gene is associated with Chorea-acanthocytosis (ChAc), a rare hereditary neurodegenerative disorder. The review covers essential aspects, beginning with the genetics of VPS13A, highlighting its role in the pathogenesis of ChAc, and addressing the spectrum of genetic variants involved. It delves into the structure and function of the VPS13A protein, emphasizing its presence in various tissues and its potential involvement in protein trafficking and lipid homeostasis. Molecular functions of VPS13A in the brain tissue and other cell types or tissues with respect to their role in cytoskeletal regulation and autophagy are explored. Finally, it explores the intriguing link between VPS13A mutations, lipid imbalances, and neurodegeneration, shedding light on future research directions. Overall, this review serves as a comprehensive resource for understanding the pivotal role of VPS13A in health and disease, particularly in the context of ChAc. Key words: Chorein , Tumor, Actin, Microfilament, Gene expression, Chorea-acanthocytosis.
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Affiliation(s)
- S Alkahtani
- Department of Zoology, College of Science, King Saud University, Riyadh, Saudi Arabia.
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2
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Jahn H, Bartoš L, Dearden GI, Dittman JS, Holthuis JCM, Vácha R, Menon AK. Phospholipids are imported into mitochondria by VDAC, a dimeric beta barrel scramblase. Nat Commun 2023; 14:8115. [PMID: 38065946 PMCID: PMC10709637 DOI: 10.1038/s41467-023-43570-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 11/13/2023] [Indexed: 12/17/2023] Open
Abstract
Mitochondria are double-membrane-bounded organelles that depend critically on phospholipids supplied by the endoplasmic reticulum. These lipids must cross the outer membrane to support mitochondrial function, but how they do this is unclear. We identify the Voltage Dependent Anion Channel (VDAC), an abundant outer membrane protein, as a scramblase-type lipid transporter that catalyzes lipid entry. On reconstitution into membrane vesicles, dimers of human VDAC1 and VDAC2 catalyze rapid transbilayer translocation of phospholipids by a mechanism that is unrelated to their channel activity. Coarse-grained molecular dynamics simulations of VDAC1 reveal that lipid scrambling occurs at a specific dimer interface where polar residues induce large water defects and bilayer thinning. The rate of phospholipid import into yeast mitochondria is an order of magnitude lower in the absence of VDAC homologs, indicating that VDACs provide the main pathway for lipid entry. Thus, VDAC isoforms, members of a superfamily of beta barrel proteins, moonlight as a class of phospholipid scramblases - distinct from alpha-helical scramblase proteins - that act to import lipids into mitochondria.
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Affiliation(s)
- Helene Jahn
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Ladislav Bartoš
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
| | - Grace I Dearden
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Jeremy S Dittman
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Joost C M Holthuis
- Department of Molecular Cell Biology, University of Osnabrück, Osnabrück, 49076, Germany
| | - Robert Vácha
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic.
- National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic.
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA.
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Naito T, Yang H, Koh DHZ, Mahajan D, Lu L, Saheki Y. Regulation of cellular cholesterol distribution via non-vesicular lipid transport at ER-Golgi contact sites. Nat Commun 2023; 14:5867. [PMID: 37735529 PMCID: PMC10514280 DOI: 10.1038/s41467-023-41213-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 08/28/2023] [Indexed: 09/23/2023] Open
Abstract
Abnormal distribution of cellular cholesterol is associated with numerous diseases, including cardiovascular and neurodegenerative diseases. Regulated transport of cholesterol is critical for maintaining its proper distribution in the cell, yet the underlying mechanisms remain unclear. Here, we show that lipid transfer proteins, namely ORP9, OSBP, and GRAMD1s/Asters (GRAMD1a/GRAMD1b/GRAMD1c), control non-vesicular cholesterol transport at points of contact between the ER and the trans-Golgi network (TGN), thereby maintaining cellular cholesterol distribution. ORP9 localizes to the TGN via interaction between its tandem α-helices and ORP10/ORP11. ORP9 extracts PI4P from the TGN to prevent its overaccumulation and suppresses OSBP-mediated PI4P-driven cholesterol transport to the Golgi. By contrast, GRAMD1s transport excess cholesterol from the Golgi to the ER, thereby preventing its build-up. Cells lacking ORP9 exhibit accumulation of cholesterol at the Golgi, which is further enhanced by additional depletion of GRAMD1s with major accumulation in the plasma membrane. This is accompanied by chronic activation of the SREBP-2 signalling pathway. Our findings reveal the importance of regulated lipid transport at ER-Golgi contacts for maintaining cellular cholesterol distribution and homeostasis.
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Affiliation(s)
- Tomoki Naito
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Haoning Yang
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Dylan Hong Zheng Koh
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore
| | - Divyanshu Mahajan
- School of Biological Sciences, Nanyang Technological University, Singapore, 637551, Singapore
| | - Lei Lu
- School of Biological Sciences, Nanyang Technological University, Singapore, 637551, Singapore
| | - Yasunori Saheki
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, 308232, Singapore.
- Institute of Resource Development and Analysis, Kumamoto University, Kumamoto, 860-0811, Japan.
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Kim H, Park J, Kim H, Ko N, Park J, Jang E, Yoon S, Diaz J, Lee C, Jun Y. Structures of Vac8-containing protein complexes reveal the underlying mechanism by which Vac8 regulates multiple cellular processes. Proc Natl Acad Sci U S A 2023; 120:e2211501120. [PMID: 37094131 PMCID: PMC10161063 DOI: 10.1073/pnas.2211501120] [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: 07/06/2022] [Accepted: 03/30/2023] [Indexed: 04/26/2023] Open
Abstract
Vac8, a yeast vacuolar protein with armadillo repeats, mediates various cellular processes by changing its binding partners; however, the mechanism by which Vac8 differentially regulates these processes remains poorly understood. Vac8 interacts with Nvj1 to form the nuclear-vacuole junction (NVJ) and with Atg13 to mediate cytoplasm-to-vacuole targeting (Cvt), a selective autophagy-like pathway that delivers cytoplasmic aminopeptidase I directly to the vacuole. In addition, Vac8 associates with Myo2, a yeast class V myosin, through its interaction with Vac17 for vacuolar inheritance from the mother cell to the emerging daughter cell during cell divisions. Here, we determined the X-ray crystal structure of the Vac8-Vac17 complex and found that its interaction interfaces are bipartite, unlike those of the Vac8-Nvj1 and Vac8-Atg13 complexes. When the key amino acids present in the interface between Vac8 and Vac17 were mutated, vacuole inheritance was severely impaired in vivo. Furthermore, binding of Vac17 to Vac8 prevented dimerization of Vac8, which is required for its interactions with Nvj1 and Atg13, by clamping the H1 helix to the ARM1 domain of Vac8 and thereby preventing exposure of the binding interface for Vac8 dimerization. Consistently, the binding affinity of Vac17-bound Vac8 for Nvj1 or Atg13 was markedly lower than that of free Vac8. Likewise, free Vac17 had no affinity for the Vac8-Nvj1 and Vac8-Atg13 complexes. These results provide insights into how vacuole inheritance and other Vac8-mediated processes, such as NVJ formation and Cvt, occur independently of one another.
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Affiliation(s)
- Hyejin Kim
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, South Korea
| | - Jihyeon Park
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
| | - Hyunwoo Kim
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, South Korea
| | - Naho Ko
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
| | - Jumi Park
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, South Korea
| | - Eunhong Jang
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
| | - So Young Yoon
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
| | - Joyce Anne R. Diaz
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
| | - Changwook Lee
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, South Korea
| | - Youngsoo Jun
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju61005, South Korea
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Rogers JR, Geissler PL. Ceramide-1-phosphate transfer protein enhances lipid transport by disrupting hydrophobic lipid-membrane contacts. PLoS Comput Biol 2023; 19:e1010992. [PMID: 37036851 PMCID: PMC10085062 DOI: 10.1371/journal.pcbi.1010992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 03/03/2023] [Indexed: 04/11/2023] Open
Abstract
Cellular distributions of the sphingolipid ceramide-1-phosphate (C1P) impact essential biological processes. C1P levels are spatiotemporally regulated by ceramide-1-phosphate transfer protein (CPTP), which efficiently shuttles C1P between organelle membranes. Yet, how CPTP rapidly extracts and inserts C1P into a membrane remains unknown. Here, we devise a multiscale simulation approach to elucidate biophysical details of CPTP-mediated C1P transport. We find that CPTP binds a membrane poised to extract and insert C1P and that membrane binding promotes conformational changes in CPTP that facilitate C1P uptake and release. By significantly disrupting a lipid's local hydrophobic environment in the membrane, CPTP lowers the activation free energy barrier for passive C1P desorption and enhances C1P extraction from the membrane. Upon uptake of C1P, further conformational changes may aid membrane unbinding in a manner reminiscent of the electrostatic switching mechanism used by other lipid transfer proteins. Insertion of C1P into an acceptor membrane, eased by a decrease in membrane order by CPTP, restarts the transfer cycle. Most notably, we provide molecular evidence for CPTP's ability to catalyze C1P extraction by breaking hydrophobic C1P-membrane contacts with compensatory hydrophobic lipid-protein contacts. Our work, thus, provides biophysical insights into how CPTP efficiently traffics C1P between membranes to maintain sphingolipid homeostasis and, additionally, presents a simulation method aptly suited for uncovering the catalytic mechanisms of other lipid transfer proteins.
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Affiliation(s)
- Julia R Rogers
- Department of Chemistry, University of California, Berkeley, California, United States of America
| | - Phillip L Geissler
- Department of Chemistry, University of California, Berkeley, California, United States of America
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America
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Utilization of n-alkane and roles of lipid transfer proteins in Yarrowia lipolytica. World J Microbiol Biotechnol 2023; 39:97. [PMID: 36781616 PMCID: PMC9925530 DOI: 10.1007/s11274-023-03541-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Accepted: 02/03/2023] [Indexed: 02/15/2023]
Abstract
Yarrowia lipolytica, a dimorphic yeast belonging to the Ascomycota, has potent abilities to utilize hydrophobic compounds, such as n-alkanes and fatty acids, as carbon and energy sources. Yarrowia lipolytica can synthesize and accumulate large amounts of lipids, making it a promising host to produce various lipids and convert n-alkanes to useful compounds. For advanced use of Y. lipolytica in these applications, it is necessary to understand the metabolism of these hydrophobic compounds in this yeast and the underlying molecular mechanisms. In this review, current knowledge on the n-alkane metabolism and how this is regulated in Y. lipolytica is summarized. Furthermore, recent studies revealed that lipid transfer proteins are involved in the utilization of n-alkanes and the regulation of cell morphology in response to n-alkanes. This review discusses the roles of membrane lipids in these processes in Y. lipolytica.
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Aboufares El Alaoui A, Buhl E, Galizia S, Hodge JJL, de Vivo L, Bellesi M. Increased interaction between endoplasmic reticulum and mitochondria following sleep deprivation. BMC Biol 2023; 21:1. [PMID: 36600217 PMCID: PMC9814192 DOI: 10.1186/s12915-022-01498-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 12/07/2022] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND Prolonged cellular activity may overload cell function, leading to high rates of protein synthesis and accumulation of misfolded or unassembled proteins, which cause endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR) to re-establish normal protein homeostasis. Previous molecular work has demonstrated that sleep deprivation (SD) leads to ER stress in neurons, with a number of ER-specific proteins being upregulated to maintain optimal cellular proteostasis. It is still not clear which cellular processes activated by sleep deprivation lead to ER- stress, but increased cellular metabolism, higher request for protein synthesis, and over production of oxygen radicals have been proposed as potential contributing factors. Here, we investigate the transcriptional and ultrastructural ER and mitochondrial modifications induced by sleep loss. RESULTS We used gene expression analysis in mouse forebrains to show that SD was associated with significant transcriptional modifications of genes involved in ER stress but also in ER-mitochondria interaction, calcium homeostasis, and mitochondrial respiratory activity. Using electron microscopy, we also showed that SD was associated with a general increase in the density of ER cisternae in pyramidal neurons of the motor cortex. Moreover, ER cisternae established new contact sites with mitochondria, the so-called mitochondria associated membranes (MAMs), important hubs for molecule shuttling, such as calcium and lipids, and for the modulation of ATP production and redox state. Finally, we demonstrated that Drosophila male mutant flies (elav > linker), in which the number of MAMs had been genetically increased, showed a reduction in the amount and consolidation of sleep without alterations in the homeostatic sleep response to SD. CONCLUSIONS We provide evidence that sleep loss induces ER stress characterized by increased crosstalk between ER and mitochondria. MAMs formation associated with SD could represent a key phenomenon for the modulation of multiple cellular processes that ensure appropriate responses to increased cell metabolism. In addition, MAMs establishment may play a role in the regulation of sleep under baseline conditions.
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Affiliation(s)
- Amina Aboufares El Alaoui
- grid.7010.60000 0001 1017 3210Department of Experimental and Clinical Medicine, Marche Polytechnic University, Ancona, Italy ,grid.5602.10000 0000 9745 6549School of Biosciences and Veterinary Medicine, University of Camerino, Camerino, Italy
| | - Edgar Buhl
- grid.5337.20000 0004 1936 7603School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Sabrina Galizia
- grid.5337.20000 0004 1936 7603School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - James J. L. Hodge
- grid.5337.20000 0004 1936 7603School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Luisa de Vivo
- grid.5337.20000 0004 1936 7603School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK ,grid.5602.10000 0000 9745 6549School of Pharmacy, University of Camerino, Camerino, Italy
| | - Michele Bellesi
- grid.5602.10000 0000 9745 6549School of Biosciences and Veterinary Medicine, University of Camerino, Camerino, Italy ,grid.5337.20000 0004 1936 7603School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
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8
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Ghavami M, Fairn GD. Endoplasmic reticulum-Phagosome contact sites from the cradle to the grave. Front Cell Dev Biol 2022; 10:1074443. [PMID: 36619860 PMCID: PMC9813420 DOI: 10.3389/fcell.2022.1074443] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 12/05/2022] [Indexed: 12/24/2022] Open
Abstract
Phagocytosis is a key component of the innate immune system used to ingest apoptotic cells and microorganisms for their destruction and recycling of macromolecules and the presentation of antigens to adaptive immune system cells. The newly formed vacuole or nascent phagosome undergoes a maturation process reminiscent of the classical endocytic maturation process, reaching a highly degradative phagolysosome stage before its tubulovesicular breakdown into lysosomes. The process is highly regulated and can be disrupted by various pathogenic organisms. The exchange of proteins, lipids, and other metabolites between organelles, including maturing phagosomes, is enabled by two processes, vesicular and non-vesicular transport at membrane contact sites (MCS). For decades the specific role(s) of the endoplasmic reticulum (ER) in phagocytosis has been the subject of much debate. In parallel, the last two decades have seen a burst in research on the numerous roles of ER contact sites and resident proteins in all aspects of organelle biology. Here, in this minireview, we describe ER-phagosome contact sites' functions from the early stages of particle engulfment to the phagolysosome dissolution into lysosomes. We also discuss several aspects of ER-phagosome contact sites that remain to be explored.
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Affiliation(s)
- Mahlegha Ghavami
- Department of Pathology, Dalhousie University, Halifax, NS, Canada,Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada
| | - Gregory D. Fairn
- Department of Pathology, Dalhousie University, Halifax, NS, Canada,Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada,*Correspondence: Gregory D. Fairn,
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Creating and sensing asymmetric lipid distributions throughout the cell. Emerg Top Life Sci 2022; 7:7-19. [PMID: 36373850 DOI: 10.1042/etls20220028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 10/24/2022] [Accepted: 11/01/2022] [Indexed: 11/16/2022]
Abstract
A key feature of eukaryotic cells is the asymmetric distribution of lipids along their secretory pathway. Because of the biological significance of these asymmetries, it is crucial to define the mechanisms which create them. Extensive studies have led to the identification of lipid transfer proteins (LTPs) that work with lipid-synthesizing enzymes to carry lipids between two distinct membranes in a directional manner, and are thus able to create asymmetries in lipid distribution throughout the cell. These networks are often in contact sites where two organelle membranes are in close proximity for reasons we have only recently started to understand. A question is whether these networks transfer lipids en masse within the cells or adjust the lipid composition of organelle membranes. Finally, recent data have confirmed that some networks organized around LTPs do not generate lipid asymmetries between membranes but sense them and rectify the lipid content of the cell.
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Hullin-Matsuda F, Colosetti P, Rabia M, Luquain-Costaz C, Delton I. Exosomal lipids from membrane organization to biomarkers: Focus on an endolysosomal-specific lipid. Biochimie 2022; 203:77-92. [DOI: 10.1016/j.biochi.2022.09.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 09/22/2022] [Accepted: 09/26/2022] [Indexed: 11/30/2022]
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Egea PF. Moving Lipids, by the Numbers. CONTACT 2022; 5. [PMID: 36128030 PMCID: PMC9484574 DOI: 10.1177/25152564221103080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Pascal F. Egea
- Department of Biological Chemistry, School of Medicine, University of California Los Angeles, Los Angeles, USA
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Levine TP. Sequence Analysis and Structural Predictions of Lipid Transfer Bridges in the Repeating Beta Groove (RBG) Superfamily Reveal Past and Present Domain Variations Affecting Form, Function and Interactions of VPS13, ATG2, SHIP164, Hobbit and Tweek. CONTACT (THOUSAND OAKS (VENTURA COUNTY, CALIF.)) 2022; 5:251525642211343. [PMID: 36571082 PMCID: PMC7613979 DOI: 10.1177/25152564221134328] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Lipid transfer between organelles requires proteins that shield the hydrophobic portions of lipids as they cross the cytoplasm. In the last decade a new structural form of lipid transfer protein (LTP) has been found: long hydrophobic grooves made of beta-sheet that bridge between organelles at membrane contact sites. Eukaryotes have five families of bridge-like LTPs: VPS13, ATG2, SHIP164, Hobbit and Tweek. These are unified into a single superfamily through their bridges being composed of just one domain, called the repeating beta groove (RBG) domain, which builds into rod shaped multimers with a hydrophobic-lined groove and hydrophilic exterior. Here, sequences and predicted structures of the RBG superfamily were analyzed in depth. Phylogenetics showed that the last eukaryotic common ancestor contained all five RBG proteins, with duplicated VPS13s. The current set of long RBG protein appears to have arisen in even earlier ancestors from shorter forms with 4 RBG domains. The extreme ends of most RBG proteins have amphipathic helices that might be an adaptation for direct or indirect bilayer interaction, although this has yet to be tested. The one exception to this is the C-terminus of SHIP164, which instead has a coiled-coil. Finally, the exterior surfaces of the RBG bridges are shown to have conserved residues along most of their length, indicating sites for partner interactions almost all of which are unknown. These findings can inform future cell biological and biochemical experiments.
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