title: Crystal twinning of human MD-2 recognizing endotoxin cores of lipopolysaccharide.
abstract: Twinning of crystals causes overlapping of two or more reciprocal lattice points, and hence structure amplitudes for a single crystalline domain are hardly obtained from X-ray diffraction intensities. MD-2 protein forms a stable complex with Toll-like receptor 4 and recognizes bacterial lipopolysaccharide (LPS). Excessive immune responses activated by LPS cause septic shocks. Saccharide-trimmed human MD-2 crystallizes in the tetragonal form with apparent Laue symmetry of 4/mmm, and diffraction intensities from these crystals indicate crystal twinning. The crystal consists of two different domains, A and B. The c(A) axis of domain A coincides with the c(B) axis of domain B with a smaller lattice, and the a(A) axis corresponds to the (a(B) + b(B)) axis. This twinning severely imposes difficulty in structure determination. Through optimization of cryoprotectant, domain A was thoroughly transformed into domain B. The crystal containing only domain B is in space group P4(1)2(1)2 with one MD-2 molecule in the asymmetric unit. The structure of this form of MD-2 as well as its complex with antiendotoxic lipid IVa was successfully determined using the multiple isomorphous replacement method.
authors.affiliation: Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
authors.forename: Umeharu
authors.initials: U
authors.lastname: Ohto
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Satow
mesh_terms: D018360:Crystallography, X-Ray; D004731:Endotoxins / Q000737:chemistry*; D006801:Humans; D008070:Lipopolysaccharides / Q000737:chemistry*; D051218:Lymphocyte Antigen 96 / Q000737:chemistry*; D008958:Models, Molecular
chemical_list: D004731:Endotoxins; C495377:LY96 protein, human; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96