Structure and function of new-type exfoliative toxin from Staphylococcus hyicus.

Graduate School of Science, Hiroshima University* Graduate School of Biomedical Science, Hiroshima Uneversity, Japan**
○Katsuo Katayanagi* Kenji Yamamoto* Yasuyuki Fudaba** Takayuki Yamaguchi** Motoyuki Sugai**

Exfoliative toxin (ET) is an exotoxin derived from staphylococcal species, and it causes blisters in human and animal skin. This kind of skin syndrome (staphylococcal scalded skin syndrome: SSSS) is a generalized blistering skin disease that is primarily a disease of young children and neonates. In addition to ET from staphylococcus aureus, new type of ET from staphylococcus hyicus, which lives on the skin of the pigs, has been identified by gene analysis. They were classified to four isomers as ExhA, ExhB, ExhC and ExhD. In this study, we crystallized the four isomers to clarify the difference in the viewpoints of the structure and function relationships. The protein we used was expressed by E. coli.
Both of ExhA and ExhD were crystallized by hanging drop vapor diffusion method, whereas ExhB was crystallized by microbatch. The resolutions of ExhA, ExhB, and ExhD were 1.9 Å, 1.7 Å, and 2.1 Å, respectively, and space groups were P2221, P212121, and, P212121 respectively. Diffraction images were digitalized and merged using the programs HKL2000 and XdisplayF, and Rsym was estimated to be 0.073, 0.045, 0.075 for ExhA, B, and D. The number of molecules per asymmetric unit was calculated to be 2 for ExhA and B and 3 for ExhD. Although the ExhC crystal has grown to a large size, the resolution of this crystal was only 3.2 Å, and the lattice parameter was a = 130.78 Å, b = 235.34 Å, c = 265.96 Å, and no good solution has been found yet.
Molecular replacement was applied using the coordinate set of ETs. Crystallographic refinement is now under way and the backbone structure was found to be quite similar as exfoliative toxins. But some different conformation of active site structure was found.