Concretely, they constitute a family of sterol and phosphoinositide binding and transfer proteins in eukaryotes[2] 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.

[3] Although sterol transfer is proposed to occur at regions where organelle membranes are closely apposed, disruption of endoplasmic reticulum-plasma membrane contact sites do not have major effects on sterol transfer, though phospholipid homeostasis is perturbed.

[6] In mammalian cells, some ORPs function as sterol sensors that regulate the assembly of protein complexes in response to changes in cholesterol levels.

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.

In addition, they were shown to be involved in other processes such as immune regulatory functions and brain homeostasis.

[9][10] All oxysterol related proteins (ORP) contain a core lipid-binding domain (ORD), which has a characteristic amino acids sequence, EQVSHHPP.

As part of the Lipid Transfer proteins (LTPs) family, ORPs have different and variate functions.

This functions include signaling, vesicular trafficking, lipid metabolism and nonvesicular sterol transport.

In yeast (Saccharomyces cerevisiæ) we can find 7 ORP genes called OSH1-7, but they have some additional names as well.