Oxysterol-binding protein
| Oxysterol-binding protein | |||||||||
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Crystallographic structure of the oxysterol-binding protein (rainbow color cartoon, N-terminus = blue, C-terminus = red) bound to 7-hydroxycholesterol (stick diagram, carbon = white, oxygen = red).
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| Identifiers | |||||||||
| Symbol | Oxysterol_BP | ||||||||
| Pfam | PF01237 | ||||||||
| InterPro | IPR000648 | ||||||||
| PROSITE | PDOC00774 | ||||||||
| OPM superfamily | 173 | ||||||||
| OPM protein | 1zi7 | ||||||||
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| Available protein structures: | |
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| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
The oxysterol-binding protein (OSBP)-related proteins (ORPs) are a family of lipid transfer proteins (LTPs). Concretely, they constitute a family of sterol and phosphoinositide binding and transfer proteins in eukaryotes that are conserved from yeast to humans. They are lipid-binding proteins implicated in many cellular processes related with oxysterol, including signaling, vesicular trafficking, lipid metabolism, and nonvesicular sterol transport.
In yeast cells, it is probable that ORPs function as sterol transporters, perhaps in regions where organelle membranes are closely apposed. Various ORPs confine at membrane contacts sites (MCS), where endoplasmic reticulum (ER) is apposed with other organelle limiting membranes. Yeast ORPs also participate in vesicular trafficking, although their role is unclear. In mammalian cells, some ORPs function as sterol sensors that regulate the assembly of protein complexes in response to changes in cholesterol levels. By that means, ORPs most likely affect organelle membrane lipid compositions, with impacts on signaling and vesicle transport, but also cellular lipid metabolism.
Oxysterol is a cholesterol metabolite that can be produced through enzymatic or radical processes. Oxysterols, that are the 27-carbon products of cholesterol oxidation by both enzymic and non-enzymic mechanisms, constitute a large family of lipids involved in a plethora of physiological processes. Studies identifying the specific cellular targets of oxysterol indicate that several oxysterols may be regulators of cellular lipid metabolism via control of gene transcription. In addition, they were shown to be involved in other processes such as immune regulatory functions and brain homeostasis.
All oxysterol related proteins (ORP) contain a core lipid-binding domain (ORD), which has a characteristic amino acids sequence, EQVSHHPP. The most studied ORP are human and yeast ones, and the only OSBP-ORP whose structure is completely known is the Kes1p, also called Osh4p, a yeast one. Six different protein domains and structural motifs types are found in OSBP-ORPs.
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