Possible Orientation of the Fatty Acid Chains in Lipopolysaccharide

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Abstract
The fatty acid chains of the lipid A component of Salmonella lipopolysaccharides are hexagonally packed with a lattice periodicity of 4.1 .ANG.. The smallest subunit of this lattice consists of a disaccharide to which 7 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, the angles that the hydrocarbon chains make with the planes of the 2 sugar residues should be nearly vertical. The planes of both sugar residues should be approximately coplanar, forming an angle of about 180.degree. with each other. Conformation angles for all the theoretically possible linkages of the disaccharide and of the linkages of the fatty acid residues were calculated. Between the 2 N-acylglucosamine residues, .beta.-1,4, .alpha.-1,6 or .beta.-1,6 linkages are theoretically possible. The experimentally found .beta.-1,6 linkage has the largest degrees of freedom for its conformation angles.