Crystal twinning of human MD-2 recognizing endotoxin cores of lipopolysaccharide

• Published in: Journal of synchrotron radiation Vol. 15; no. 3; pp. 262 - 265
• Main Authors: Ohto, Umeharu, Satow, Yoshinori
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.05.2008
• Subjects: crystal twinning; Crystallography, X-Ray; Diffraction Structural Biology; endotoxin; Endotoxins - chemistry; Humans; innate immunity; Lipopolysaccharides - chemistry; Lymphocyte Antigen 96 - chemistry; Models, Molecular
• DOI: 10.1107/S0909049507056531
• ISSN: 1600-5775; 0909-0495

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 cA axis of domain A coincides with the cB axis of domain B with a smaller lattice, and the aA axis corresponds to the (aB + bB) 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 P41212 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.