The tryptophan (W)-repressor binding protein A (WrbA) identified as an Escherichia coli stationary-phase protein was proposed as the founding member of a new family of multimeric flavodoxin-like proteins implicated in oxidative-stress defense. Since WrbA is largely uncharacterized with respect to both molecular and physiological functions, the present effort is aimed at structural characterization. WrbA apoprotein was purified and used for crystallization trials at room temperature. Multicrystals of WrbA apoprotein were obtained using standard and advanced crystallization techniques. Application of additives and gelling protein for crystallization in single capillaries yielded diffraction-quality single crystals. The crystals diffracted to a resolution of 2.2 angstrom at synchrotrons DESY (X13) in Hamburg (Germany), and Elletra (XRD1) in Trieste (Italy). (c) 2005 Elsevier B.V. All rights reserved.