Crystallization of lipopolysaccharide from a Salmonella typhimurium semi-rough (SR) mutant

Salmonella typhimurium SR-form lipopolysaccharide (LPS), consisting of a si ngle repeating unit of the O-antigenic polysaccharide, linked to the R-core consisting of oligosaccharide that is, in turn, linked to lipid A, formed crystals whose shapes were hexagonal plates, discoids, and solid columns wh en precipitated by the addition of 2 volumes of 95% ethanol containing 375 mM MgCl2 and kept in 70% ethanol containing 250 mM MgCl2 at 4 C for 10 days , Among these crystals, the basic form is considered to be the hexagonal pl ates. Analyses of hexagonal plate crystals showed that they consist of hexa gonal lattices with a lattice constant (a axis) of 4.62 Angstrom and longit udinal axis (c axis) of approximately 100 Angstrom. In X-ray diffraction pa tterns in the low-angle region, crystals of S, typhimurium SR-form LPS exhi bited much less distinct reflections when compared with crystals of synthet ic Escherichia coli-type lipid A. In contrast to the previous finding that S, minnesota S-form LPS possessing the O-antigenic polysaccharide does not crystallize under the same experimental conditions as used in the present s tudy, the presence of a single repeating unit of the O-antigenic polysaccha ride does not inhibit crystallization.