Crystallization and preliminary X-ray analysis of the Streptomyces olivaceoviridis NgcE binding protein of the ABC transporter for N-acetylglucosamine.

The NgcE protein binds N-acetylglucosamine (GIcNAc) as well asN,N'-diacetylchitobiose and is a component of the ABC transporter Ngc for GIcNAc uptake in Streptomyces olivaceoviridis. After cloning the corresponding gene in an Escherichia coli host, the NgcE protein was overproduced in a soluble form within the cytoplasm and purified to homogeneity by four consecutive chromatographic processes. Crystals of NgcE that grew in the presence of 1 mM GlcNAc,20%(w/v) PEG MME 2000 and 100 mM Tris-HCI pH 8.5 had a plate-like shape and belonged to either space group P21212 (unit-cell parameters a = 59.9, b = 153.0, c = 41.7 A) or P212121 (a = 58.1, b = 96.3, c = 151.7 A). The former crystals diffracted to 1.8 A resolution andthe latter to 2.2 A. Selenomethionine-containing crystals were generated under the same conditions and belonged to space group P212121 with unit-cell parameters a = 58.4, b = 96.6, c = 152.5 A, and diffracted to 2.0 A resolution.