Small and medium-angle X-ray analysis of bacterial lipoteichoic acid phase structure.

X-ray scattering analysis was performed on various types of bacterial lipoteichoic acid in solution. The X-ray data show that all samples investigated were characterized by a similar micellar ultrastructure (hydrophilic moiety on the outside) with a fatty acid chain conformation of the disordered, alpha-type at all temperatures between 5 degrees-53 degrees C. The size distribution of Staphylococcus aureus lipoteichoic acid micelles was sufficiently homogeneous to determine their size and some related molecular parameters by detailed small-angle X-ray scattering analysis. Nearly independent of the degree of D-alanine substitution and the ionic strength of the aqueous dispersion, an average micelle contained about 150 lipoteichoic acid molecules arranged in a spherical assembly with a diameter of about 22 nm, whereby the hydrophilic region occupied an outer shell of about 8.5 nm thickness. Based on the average chain length of lipoteichoic acid, it could be estimated that each glycerophosphate residue contributed by about 0.34 nm to the thickness of the hydrophilic shell as compared to a theoretical value of approximately 0.8 nm for a fully extended chain conformation, indicating a highly coiled conformation of the hydrophilic chain. The bearing of these findings on the properties of membrane-associated and secreted lipoteichoic acids is discussed.