Structure of Yeast OSBP-Related Protein Osh1 Reveals Key Determinants for Lipid Transport and Protein Targeting at the Nucleus-Vacuole Junction

Manik, M.K.; Yang, Hong-So; Tong, Junsen; Im, Young Jun

doi:10.1016/j.str.2017.02.010

Cited by 49 publications

(59 citation statements)

References 49 publications

(89 reference statements)

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“…We observed that the tunnel bottoms of LAM SDs are occupied by several water molecules, not by the ligand. The presence of water clusters in the tunnel bottom was as also observed in the sterol-bound states of oxysterol-binding proteins, Osh1 and Osh4 (25,31). Therefore, if we exclude the space for the water clusters in the tunnel bottom of StART domains, the cavity volumes in the closed conformation of the Ω1-loop are too small to accommodate the sterol molecules.…”

Section: Discussionmentioning

confidence: 77%

Structural basis of sterol recognition and nonvesicular transport by lipid transfer proteins anchored at membrane contact sites

Tong

Manik

2018

Proc. Natl. Acad. Sci. U.S.A.

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Membrane contact sites (MCSs) in eukaryotic cells are hotspots for lipid exchange, which is essential for many biological functions, including regulation of membrane properties and protein trafficking. Lipid transfer proteins anchored at membrane contact sites (LAMs) contain sterol-specific lipid transfer domains [StARkin domain (SD)] and multiple targeting modules to specific membrane organelles. Elucidating the structural mechanisms of targeting and ligand recognition by LAMs is important for understanding the interorganelle communication and exchange at MCSs. Here, we determined the crystal structures of the yeast Lam6 pleckstrin homology (PH)-like domain and the SDs of Lam2 and Lam4 in the apo form and in complex with ergosterol. The Lam6 PH-like domain displays a unique PH domain fold with a conserved N-terminal α-helix. The Lam6 PH-like domain lacks the basic surface for phosphoinositide binding, but contains hydrophobic patches on its surface, which are critical for targeting to endoplasmic reticulum (ER)-mitochondrial contacts. Structures of the LAM SDs display a helix-grip fold with a hydrophobic cavity and a flexible Ω1-loop as a lid. Ergosterol is bound to the pocket in a head-down orientation, with its hydrophobic acyl group located in the tunnel entrance. The Ω1-loop in an open conformation is essential for ergosterol binding by direct hydrophobic interaction. Structural comparison suggested that the sterol binding mode of the Lam2 SD2 is likely conserved among the sterol transfer proteins of the StARkin superfamily. Structural models of full-length Lam2 correlated with the sterol transport function at the membrane contact sites.

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Section: Discussionmentioning

confidence: 77%

Structural basis of sterol recognition and nonvesicular transport by lipid transfer proteins anchored at membrane contact sites

Tong

Manik

2018

Proc. Natl. Acad. Sci. U.S.A.

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“…ORP2 belongs, based on its amino acid sequence and gene structure, to ORP subfamily II, together with the closely related ORP1 [3]. ORPs share a characteristic β-barrel-resembling ligand-binding domain designated OSBP-related domain (ORD) in their carboxy-terminal region [3,[6][7][8]. While all other mammalian OSBPL/Osbpl genes encode ORP proteins of the 'long' subtype, carrying an amino-terminal extension that contains a pleckstrin homology (PH) domain, ORP2 only exists as a 'short' subtype protein lacking a pH domain ( Fig.…”

Section: Introductionmentioning

confidence: 99%

OSBP-related protein 2 (ORP2): Unraveling its functions in cellular lipid/carbohydrate metabolism, signaling and F-actin regulation

Olkkonen

Koponen

Arora

2019

The Journal of Steroid Biochemistry and Molecular Biology

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Oxysterol-binding protein (OSBP)-related proteins (ORPs) constitute a family of intracellular lipid-binding/ transport proteins (LTPs) in eukaryotes. They typically have a modular structure comprising a lipid-binding domain and membrane targeting determinants, being thus suited for function at membrane contact sites. Among the mammalian ORPs, ORP2/OSBPL2 is the only member that only exists as a 'short' variant lacking a membrane-targeting pleckstrin homology domain. ORP2 is expressed ubiquitously and has been assigned a multitude of functions. Its OSBP-related domain binds cholesterol, oxysterols, and phosphoinositides, and its overexpression enhances cellular cholesterol efflux. Consistently, the latest observations suggest a function of ORP2 in cholesterol transport to the plasma membrane (PM) in exchange for phosphatidylinositol 4,5-bisphosphate (PI4,5P 2), with significant impacts on the concentrations of PM cholesterol and PI4,5P 2. On the other hand, ORP2 localizes at the surface of cytoplasmic lipid droplets (LDs) and at endoplasmic-reticulum-LD contact sites, and its depletion modifies cellular triglyceride (TG) metabolism. Study in an adrenocortical cell line further suggested a function of ORP2 in the synthesis of steroid hormones. Our recent knockout of ORP2 in human hepatoma cells revealed its function in hepatocellular PI3K/Akt signaling, glucose and triglyceride metabolism, as well as in actin cytoskeletal regulation, cell adhesion, migration and proliferation. ORP2 was shown to interact physically with F-actin regulators such as DIAPH1, ARHGAP12, SEPT9 and MLC12, as well as with IQGAP1 and the Cdc37-Hsp90 chaperone complex controlling the activity of Akt. Interestingly, mutations in OSBPL2 encoding ORP2 are associated with autosomal dominant non-syndromic hearing loss, and the protein was found to localize in cochlear hair cell stereocilia. The functions assigned to ORP2 suggest that this protein, in concert with other LTPs, controls the subcellular distribution of cholesterol in various cell types and steroid hormone synthesis in adrenocortical cells. However, it also impacts cellular TG and carbohydrate metabolism and F-actin-dependent functions, revealing a bewildering spectrum of activities.

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“…Although NVJs have not been specifically shown to mediate lipid transfer between the vacuole and NE, interorganelle contact sites often serve as sites of lipid exchange (Kornmann et al, 2009;Elbaz-Alon et al, 2014) due to their close apposition and enrichment of lipid-exchanging factors. The ergosterol-and PI(4)P-binding protein Osh1 (Manik et al, 2017), which is found at NVJs and interacts with Nvj1 (Jeong et al, 2017;Kvam and Goldfarb, 2004;Levine and Munro, 2001), belongs to the oxysterol-binding homology protein family that can aid in lipid transfer between membranes (de Saint-Jean et al, 2011). Additionally, LDs are thought to promote lipid transfer between organelles, potentially through "lipid bridges" (Schuldiner and Bohnert, 2017).…”

Section: Discussionmentioning

confidence: 99%

Nuclear envelope-vacuole contacts mitigate nuclear pore complex assembly stress

Lord

Wente

2020

Preprint

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The intricacy of nuclear pore complex (NPC) biogenesis imposes risks of failure that can cause defects in nuclear transport and nuclear envelope morphology, however, cellular mechanisms utilized to alleviate NPC assembly stress are not well-defined. In the budding yeast Saccharomyces cerevisiae, we demonstrate that NVJ1-and MDM1-enriched nuclear envelope (NE)-vacuole contacts increase when NPC assembly is compromised in several nup mutants, including nup116ΔGLFG cells. These interorganelle nucleus-vacuole junctions (NVJs) cooperate with lipid droplets to maintain viability and enhance NPC formation in assembly mutants. Additionally, NVJs function with ATG1 to promote vacuole-dependent remodeling in nup116ΔGLFG cells, which also correlates with proper NPC formation. Importantly, NVJs significantly improve the physiology of NPC assembly mutants, despite having only negligible effects when NPC biogenesis is unperturbed. Collectively, these results define how NE-vacuole interorganelle contacts coordinate responses to mitigate deleterious cellular effects caused by disrupted NPC assembly. SummaryHow cells respond to deleterious effects imposed by disrupted nuclear pore complex (NPC) assembly are not well-defined. The authors demonstrate nuclear envelope-vacuole interactions expand in response to perturbed NPC assembly to promote viability, nuclear envelope remodeling, and proper NPC biogenesis.

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Structure of Yeast OSBP-Related Protein Osh1 Reveals Key Determinants for Lipid Transport and Protein Targeting at the Nucleus-Vacuole Junction

Cited by 49 publications

References 49 publications

Structural basis of sterol recognition and nonvesicular transport by lipid transfer proteins anchored at membrane contact sites

Structural basis of sterol recognition and nonvesicular transport by lipid transfer proteins anchored at membrane contact sites

OSBP-related protein 2 (ORP2): Unraveling its functions in cellular lipid/carbohydrate metabolism, signaling and F-actin regulation

Nuclear envelope-vacuole contacts mitigate nuclear pore complex assembly stress

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