Resolving the space-group ambiguity of crystals of tomato fruit polygalacturonase

• Published in: Acta crystallographica. Section D, Biological crystallography. Biological crystallography., 2003-12, Vol.59 (12), p.2088-2093
• Main Authors: Heffron, Susan, Watkins, Stephan, Moeller, Rhonda, Taban, Aise Huma, Butowt, Rafal, DellaPenna, Dean, Jurnak, Frances
• Format: Article
• Language: English
• Subjects: Crystallization; Crystallography, X-Ray; Fruit - enzymology; Lycopersicon esculentum - enzymology; Models, Molecular; monoclinic; polygalacturonase; Polygalacturonase - chemistry; Protein Conformation; pseudo-orthorhombic; space-group ambiguity
• ISSN: 1399-0047; 0907-4449; 1399-0047
• DOI: 10.1107/S0907444903018092

The first polygalacturonase from a plant, tomato fruit PG2, has been crystallized and data have been collected to a resolution of 1.87 Å. The autoindexing program strongly favors one of the primitive orthorhombic cells. A plausible molecular‐replacement solution for two molecules in the asymmetric unit has been found for data assigned to space group P212121. Although the numerical criteria and the electron‐density maps are reasonable for this solution, manually adjusted models do not refine to an R factor below 0.48. Visual inspection of hkl Bragg planes does not reveal a breakdown in mm symmetry. Nevertheless, the correct space group has been determined to be P21, with similar unit‐cell parameters, a β angle of 90.04° and four molecules in the asymmetric unit. The Rsym of 0.053 for data processed in P212121 is very similar to the Rsym of 0.047 for the same data processed in P21. Comparisons of the intermediate results using the P212121 and P21 data sets are provided and the subtle indications of an initial erroneous space‐group assignment are discussed.