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The quest for an optimal limited set of effective crystallization conditions remains a challenge in macromolecular crystallography, an issue that is complicated by the large number of chemicals which have been deemed to be suitable for promoting crystal growth. The lack of rational approaches towards the selection of successful chemical space and representative combinations has led to significant overlapping conditions, which are currently present in a multitude of commercially available crystallization screens. Here, an alternative approach to the sampling of widely used PEG precipitants is suggested through the use of PEG smears, which are mixtures of different PEGs with a requirement of either neutral or cooperatively positive effects of each component on crystal growth. Four newly defined smears were classified by molecular-weight groups and enabled the preservation of specific properties related to different polymer sizes. These smears not only allowed a wide coverage of properties of these polymers, but also reduced PEG variables, enabling greater sampling of other parameters such as buffers and additives. The efficiency of the smear-based screens was evaluated on more than 220 diverse recombinant human proteins, which overall revealed a good initial crystallization success rate of nearly 50%. In addition, in several cases successful crystallizations were only obtained using PEG smears, while various commercial screens failed to yield crystals. The defined smears therefore offer an alternative approach towards PEG sampling, which will benefit the design of crystallization screens sampling a wide chemical space of this key precipitant.

Original publication

DOI

10.1107/S1399004715007968

Type

Journal article

Journal

Acta Crystallogr D Biol Crystallogr

Publication Date

08/2015

Volume

71

Pages

1627 - 1639

Keywords

PEG smear, chemical space, crystallization screen, protein crystallization, Adaptor Proteins, Signal Transducing, Carrier Proteins, Chemical Precipitation, Crystallization, Humans, Mitochondrial Membrane Transport Proteins, Mitochondrial Proteins, Mitogen-Activated Protein Kinase 1, Phosphoprotein Phosphatases, Polyethylene Glycols, Proteins, Recombinant Proteins