Acta Cryst. (2003). D59, 769±772 Wooh et al.  Sparse-matrix crystallization screens 769 short communications Acta Crystallographica Section D Biological Crystallography ISSN 0907-4449 Comparison of three commercial sparse-matrix crystallization screens Jong Wei Wooh, a,b Richard D. Kidd, b ² Jennifer L. Martin a,b,c and Bostjan Kobe a,b,c * a Department of Biochemistry and Molecular Biology, University of Queensland, Brisbane, Queensland 4072, Australia, b Institute for Molecular Bioscience and ARC Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, Queensland 4072, Australia, and c Cooperative Research Centre for Chronic Inflammatory Diseases, University of Queensland, Brisbane, Queensland 4072, Australia ² Present address: Inpharmatica Ltd, 60 Charlotte Street, London W1T 2NU, England. Correspondence e-mail: b.kobe@mailbox.uq.edu.au # 2003 International Union of Crystallography Printed in Denmark ± all rights reserved Sparse-matrix sampling using commercially available crystallization screen kits has become the most popular way of determining the preliminary crystallization conditions for macromolecules. In this study, the ef®ciency of three commercial screening kits, Crystal Screen and Crystal Screen 2 (Hampton Research), Wizard Screens I and II (Emerald BioStructures) and Personal Structure Screens 1 and 2 (Molecular Dimensions), has been compared using a set of 19 diverse proteins. 18 proteins yielded crystals using at least one crystallization screen. Surprisingly, Crystal Screens and Personal Structure Screens showed dramatically different results, although most of the crystallization formulations are identical as listed by the manufacturers. Higher molecular weight polyethylene glycols and mixed precipitants were found to be the most effective precipitants in this study. Received 11 November 2002 Accepted 4 February 2003 PDB Reference: . 1. Introduction Crystallization remains one of the major bottlenecks in macromolecular structure determination by X-ray crystallography. The search for conditions suitable for crystal growth remains largely empirical, particularly screening for initial crystallization conditions. Once initial crystals have been obtained, the conditions can usually be optimized by a more systematic approach. Because crystallization is affected by many variables and the amount of protein is usually limited, sampling of the multidimensional condition space can be challenging. Various approaches have been proposed for this task. While sampling methods such as the incom- plete factorial approach (Carter & Carter, 1979), orthogonal arrays (Kingston et al., 1994) and reverse screening (Stura et al., 1994) offer statistically superior sampling of various parameters or a more methodical route to obtaining preliminary crystals, the method of sparse-matrix screening has arguably become the most popular approach for initial crystal- lization screening. In an early application of sparse-matrix sampling, a set of 50 crystal- lization solutions was proposed based on known or published crystallization conditions for various proteins (Jancarik & Kim, 1991). Many variations of sparse-matrix screens have subsequently been developed in various laboratories and the popularity of such screens has increased through the availability of commercial kits (e.g. Crystal Screen, Hampton Research). The sparse-matrix approach was originally suggested to be well suited to auto- mation (Jancarik & Kim, 1991) and, accord- ingly, this approach has been adopted by structural genomics initiatives (Burley, 2000). Here, we posed the question whether three popular commercial screens (Crystal Screen and Crystal Screen 2, Hampton Research; Wizard Screens I and II, Emerald Bio- Structures; Personal Structure Screens 1 and 2, Molecular Dimensions) are similarly effective in crystallizing a set of 19 diverse proteins. Surprisingly, we found that the Hampton Research Crystal Screens and Molecular Dimensions Personal Structure Screens yielded quite different results, although most of the formulations are identical as listed by the manufacturers. Our study shows some trends in the ef®ciency of individual crystal- lization components in the crystallization of proteins and will help in formulating even more ef®cient crystallization screens. 2. Experimental methods The following proteins were used without further puri®cation: equine myoglobin, hen egg-white lysozyme, bovine catalase, rabbit phosphorylase B, porcine pepsin, bovine -lactalbumin, bovine trypsin, human haemo- globin, Bacillus licheniformis subtilisin Carls- berg, bovine ribonuclease A, porcine elastase (all obtained from Sigma±Aldrich), Tricho- derma longibrachiatum xylanase and Strepto- myces rubiginosus glucose isomerase (both obtained from Hampton Research). Porcine ribonuclease inhibitor (Kobe & Deisenhofer, 1993), mouse importin- (Teh et al., 1999), feline immunode®ciency virus gp36 (residues 652±784)±maltose-binding protein (MBP)