Molecular structure of bacterial endotoxin (Escherichia coli Re lipopolysaccharide): implications for formation of a novel heterogeneous lattice structure

Analyses of crystals of Escherichia coli Re lipopolysaccharide (LPS) formed after storage in 1% triethylamine indicate that the LPS molecules are asse mbled to form a monolayered structure consisting of a novel heterogeneous l attice structure, the greater part of which is occupied by one kind of latt ice (lattice I), corresponding to the acyl chain portion of lipid A, and th e remainder is occupied by the other kind of lattice (lattice II), correspo nding to the 3-deoxy-D-manno-octulosonic acid (dOclA) dimer and the N-acety lglucosamine disaccharide of lipid A. X-ray diffraction reveals that the ty pe of cell is monoclinic (a = 5.53 Angstrom, b = 27.2 Angstrom, c = 6.47 An gstrom, alpha = 90 degrees, beta = 125,8 degrees, gamma = 90 degrees), Atom ic force microscopy shows that crystals consist of multiple layers; the thi ckness of a layer corresponds to the b-axis value, and two types of surface topographies are visualized. One, regarded as the view onto the acyl chain ends, is two-dimensional arrays of oval bodies that constitute the lattice , with the lattice constants corresponding to the a and c-axes and the angl e of beta (lattice I). The other, regarded as the view onto the dOclA dimer s, is two-dimensional arrays of dromedary-back-like bodies that constitute the lattice with axes of 9.0 and 10.7 Angstrom and the angle of 65 degrees formed by both axes (lattice II). Based on these results, we present the mo lecular model of E. coli Re LPS.