Serial crystallographic analysis of protein isomorphous replacement data from a mixture of native and derivative microcrystals

Abstract

A post-experimental identification/purification procedure similar to that described in Zhanget al.[(2015),IUCrJ,2, 322–326] has been proposed for use in the treatment of multiphase protein serial crystallography (SX) diffraction snapshots. As a proof of concept, the procedure was tested using theoretical serial femtosecond crystallography (SFX) data from a mixture containing native and derivatized crystals of a protein. Two known proteins were taken as examples. Multiphase diffraction snapshots were subjected to two rounds of indexing using the programCrystFEL[Whiteet al.(2012).J. Appl. Cryst.45, 335–341]. In the first round, anab initioindexing was performed to derive a set of approximate primitive unit-cell parameters, which are roughly the average of those from the native protein and the derivative. These parameters were then used in a second round of indexing as input toCrystFEL. The results were then used to separate the diffraction snapshots into two subsets corresponding to the native and the derivative. For each test sample, integration of the two subsets of snapshots separately led to two sets of three-dimensional diffraction intensities, one belonging to the native and the other to the derivative. Based on these two sets of intensities, a conventional single isomorphous replacement (SIR) procedure solved the structure easily.