Application of profile fitting method to neutron time-of-flight protein single crystal diffraction data collected at the iBIX.

Naomine Yano,Ichiro Tanaka,Taro Yamada,Takaaki Hosoya,Katsuhiro Kusaka,Takashi Ohhara

doi:10.1038/srep36628

Abstract

We developed and employed a profile fitting method for the peak integration of neutron time-of-flight diffraction data collected by the IBARAKI Biological Crystal Diffractometer (iBIX) at the Japan Proton Accelerator Research Complex (J-PARC) for protein ribonuclease A and α-thrombin single crystals. In order to determine proper fitting functions, four asymmetric functions were evaluated using strong intensity peaks. A Gaussian convolved with two back-to-back exponentials was selected as the most suitable fitting function, and a profile fitting algorithm for the integration method was developed. The intensity and structure refinement data statistics of the profile fitting method were compared to those of the summation integration method. It was clearly demonstrated that the profile fitting method provides more accurate integrated intensities and model structures than the summation integration method at higher resolution shells. The integration component with the profile fitting method has already been implemented in the iBIX data processing software STARGazer and its user manual has been prepared.

Highlights

The peak intensities of neutron diffraction from protein single crystals are relatively weak because neutron beam intensity is lower than X-ray synchrotron intensity, and proteins have lower crystallinity than organic or inorganic compound crystals
TOF neutron protein crystallography (NPC) diffraction data processing software has been developed at each diffractometer facility independently
A Gaussian convolved with two back-to-back exponentials[32] was used as the fitting function, and was applied to the TOF neutron diffraction data of two single crystals and one cocrystal (betaine, imidazole, and picric acid (BIPa)). Because this case did not include protein single crystals measured using a diffractometer with a coupled moderator (CM), the same fitting function could not be applied to neutron diffraction data collected from the iBIX

Summary

Introduction

The peak intensities of neutron diffraction from protein single crystals are relatively weak because neutron beam intensity is lower than X-ray synchrotron intensity, and proteins have lower crystallinity than organic or inorganic compound crystals. It has been demonstrated that the application of profile fitting methods to monochromatic X-ray diffraction data can provide more accurate integrated intensities than summation integration methods, especially for weak peaks[25,26,27]. The profile fitting method for the x and y detector positions has been implemented in monochromatic X-ray single crystal data processing software such as DENZO28, MOSFLM29, and XDS30.

Results

Conclusion