Expression, crystallization and preliminary crystallographic analysis of the extracellular IgV-­like domain of the human natural killer cell inhibitory receptor p75/AIRM1

p75/AIRM1 (Siglec-7) is a sialic acid-binding Ig-like lectin recently identified as an inhibitory receptor on natural killer cells. The expression, in vitro folding, circular-dichroism spectroscopy, crystallization and preliminary X-ray characterization of the Ig-V like domain of p75/AIRM1 are reported. X-ray data were collected from a single crystal at 100 K, with a maximum useful diffraction pattern extending to 1.45 Å resolution on a synchrotron source. The crystal belongs to a primitive monoclinic space group, with unit-cell parameters a = 32.65, b = 49.72, c = 39.79 Å, α = γ = 90, β = 113°. The systematic absences indicate that the space group is P2₁. Assuming one molecule per asymmetric unit, V_M (the Matthews coefficient) was calculated to be 1.879 ų Da⁻¹ and the solvent content was estimated to be 32.01%.