SAD phasing by OASIS at different resolutions down to 0.30 nm and below

• 来源期刊: 中国物理B（英文版）
• 关键词: OASIS SAD phasing dual-space fragment extension proteins
• 年，卷（期）: 2008,（1）
• 页码范围: 1-9
• 页数: 9页
• 语种: 英文

摘要

Single-wavelength anomalous diffraction (SAD) phasing is increasingly important in solving de hove protein structures.Direct methods have been proved very efficient in SAD phasing.This paper aims at probing the low-resolution limit of direct-method SAD phasing.Two known proteins TT0570 and Tom70p were used as test samples.Sulfur-SAD data of the protein TT0570 were collected with conventional Cu-Kα source at 0.18 nm resolution.Its truncated subsets respectively at 0.21,0.30,0.35 and 0.46nm resolutions were used in the test.TT0570 Cu-Kαsulfur-SAD data have an expected Bijvoet ratio<|△F|>／<F>～0.55％.In the 0.21nm case,a single run of OASIS-DM-ARP／wARP led automatically to a model containing 1178 of the total 1206 residues all docked into the sequence.In 0.30 and 0.35 nm cases,SAD phasing by OASIS-DM led to traceable electron density maps.In the 0.40 nm case.SAD phasing by OASIS-DM resulted in a degraded electron density map,which may be difficult to trace but still contains ueeful secondary-structure information.test on real 0.33 nm selenium-SAD data of the protein Tom70p showed that even automatic model building Was not successful,the combination of manual tracing and direct-method fragment extension Was capable of significantly improving the electron-density map.This provides the possibility of effectively improving the manually built model before structure refinement is performed.