A C-terminal segment of the V₁R vasopressin receptor is unstructured in the crystal structure of its chimera with the maltose-binding protein

The V₁ vascular vasopressin receptor (V₁R) is a G-protein-coupled receptor (GPCR) involved in the regulation of body-fluid osmolality, blood volume and blood pressure. Signal transduction is mediated by the third intracellular loop of this seven-transmembrane protein as well as by the C-terminal cytoplasmic segment. A chimera of the maltose-binding protein (MBP) and the C-terminal segment of V₁R has been cloned, expressed, purified and crystallized. The crystals belong to space group P2₁, with unit-cell parameters a = 51.10, b = 66.56, c = 115.72 Å, β = 95.99°. The 1.8 Å crystal structure reveals the conformation of MBP and part of the linker region of this chimera, with the C-terminal segment being unstructured. This may reflect a conformational plasticity in the C-­terminal segment that may be necessary for proper function of V₁R.