Rapid cadmium SAD phasing at the standard wavelength (1 Å).

Saravanan Panneerselvam,Alke Meents,Inari Kursula,Esa Pekka Kumpula,Anja Burkhardt

doi:10.1107/s2059798317006970

Abstract

Cadmium ions can be effectively used to promote crystal growth and for experimental phasing. Here, the use of cadmium ions as a suitable anomalous scatterer at the standard wavelength of 1 Å is demonstrated. The structures of three different proteins were determined using cadmium single-wavelength anomalous dispersion (SAD) phasing. Owing to the strong anomalous signal, the structure of lysozyme could be automatically phased and built using a very low anomalous multiplicity (1.1) and low-completeness (77%) data set. Additionally, it is shown that cadmium ions can easily substitute divalent ions in ATP-divalent cation complexes. This property could be generally applied for phasing experiments of a wide range of nucleotide-binding proteins. Improvements in crystal growth and quality, good anomalous signal at standard wavelengths (i.e. no need to change photon energy) and rapid phasing and refinement using a single data set are benefits that should allow cadmium ions to be widely used for experimental phasing.

Highlights

High-throughput crystallography projects demand rapid data collection and robust experimental phasing procedures that are suitable for various target proteins
We showed that a single data set collected at the standard wavelength of 1 A (12 keV) is sufficient for experimental phasing as well as final structure refinement
In two of our test cases, cadmium was only mixed with the protein solution and was absent from the reservoir solutions

Summary

Introduction

High-throughput crystallography projects demand rapid data collection and robust experimental phasing procedures that are suitable for various target proteins. Metal ions play a crucial role in protein crystallization, and and model building, radiation damage is significantly reduced cadmium salts are used as a component in multiple crystal- compared with longer wavelengths, and high-resolution data lization and additive screens. Data collection and processing A single crystal was selected for each sample and X-ray and formed a chelation complex with adenosine diphosphate diffraction data sets were collected on beamline P11 at (ADP; Mayerhofer et al, 2015) This substitution could be PETRA III, DESY for HEWL and the PfActI-G1 complex generally applicable for the experimental phasing of a wide and on beamline X06DA at the Swiss Light Source (SLS) for range of nucleotide-binding proteins.

Presence of anomalous signal

Rapid phasing with highly redundant data sets

Phasing with low-resolution data sets

Conclusions and outlook