Structure of the saccharide-binding domain of the human natural killer cell inhibitory receptor p75/AIRM1.

The high-resolution crystal structure of the functional N-terminal domain from the extracellular region of the human natural killer cell inhibitory receptor p75/AIRM1 or Siglec-7 has been determined at 1.45 A resolution; it was obtained from a crystal belonging to a primitive monoclinic space group, with unit-cell parameters a = 32.65, b = 49.72, c = 39.79 A, alpha = gamma = 90, beta = 113 degrees. The structure reported here belongs to a different space group than the previously described Siglec-7 structure and was obtained using a bacterial expression system. The structure unveils the fine structural requirements adopted by a natural killer cell inhibitory receptor of the Siglec family in target-cell recognition and binding.