title: S-SAD phasing study of death receptor 6 and its solution conformation revealed by SAXS.
abstract: A subset of tumour necrosis factor receptor (TNFR) superfamily members contain death domains in their cytoplasmic tails. Death receptor 6 (DR6) is one such member and can trigger apoptosis upon the binding of a ligand by its cysteine-rich domains (CRDs). The crystal structure of the ectodomain (amino acids 1-348) of human death receptor 6 (DR6) encompassing the CRD region was phased using the anomalous signal from S atoms. In order to explore the feasibility of S-SAD phasing at longer wavelengths (beyond 2.5 Å), a comparative study was performed on data collected at wavelengths of 2.0 and 2.7 Å. In spite of sub-optimal experimental conditions, the 2.7 Å wavelength used for data collection showed potential for S-SAD phasing. The results showed that the R(ano)/R(p.i.m.) ratio is a good indicator for monitoring the anomalous data quality when the anomalous signal is relatively strong, while d''/sig(d'') calculated by SHELXC is a more sensitive and stable indicator applicable for grading a wider range of anomalous data qualities. The use of the `parameter-space screening method' for S-SAD phasing resulted in solutions for data sets that failed during manual attempts. SAXS measurements on the ectodomain suggested that a dimer defines the minimal physical unit of an unliganded DR6 molecule in solution.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, People's Republic of China.
authors.forename: Heng
authors.initials: H
authors.lastname: Ru
authors.forename: Lixia
authors.initials: L
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Ding
authors.forename: Lianying
authors.initials: L
authors.lastname: Jiao
authors.forename: Neil
authors.initials: N
authors.lastname: Shaw
authors.forename: Wenguang
authors.initials: W
authors.lastname: Liang
authors.forename: Liguo
authors.initials: L
authors.lastname: Zhang
authors.forename: Li-Wei
authors.initials: LW
authors.lastname: Hung
authors.forename: Naohiro
authors.initials: N
authors.lastname: Matsugaki
authors.forename: Soichi
authors.initials: S
authors.lastname: Wakatsuki
authors.forename: Zhi-Jie
authors.initials: ZJ
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D008969:Molecular Sequence Data; D011487:Protein Conformation; D018124:Receptors, Tumor Necrosis Factor / Q000737:chemistry*; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D018124:Receptors, Tumor Necrosis Factor; C114109:TNFRSF21 protein, human