Possible orientation of the fatty acid chains in lipopolysaccharide

The fatty acid chains of the lipid A component of lipopolysaccharides are hexagonally packed with a lattice periodicity of 4.1 A. The smallest subunit of this lattice consists of a disaccharide to which seven fatty acid chains are linked representing the hydrophobic part. Carbohydrates and substituted phosphate residues linked to them form the hydrophilic part of the molecule. Because of sterical reasons and because of the necessity of a separation of hydrophobic and hydrophilic part, we could derive that the angles of the hydrocarbon chains with the planes of the two sugar residues should be as vertical as possible and the planes of both sugar residues should be approximately coplanar forming an angle of about 180 degrees with one another. Conformation angles for all the theoretically possible linkages of the disacoharide and of the linkages of the fatty acid residues have been calculated. Between the two-N-acylglucosamine residues theoretically beta-1,4, alpha-1,6 or beta-1,6 linkages are possible. The experimentally found beta-1,6 linkage has the largest degrees of freedom for its conformation angles.