Studies on the conformation of and metal ion binding by teichoic acid of Staphylococcus aureus

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Abstract
Teichoic acid (TA) isolated from the gram-positive bacteria S. aureus binds cationic dyes like pinacyanol (PCYN), 1,9-dimethyl methylene blue, acridine orange, etc., depicting blue-shifted metachromasia, and they bind the cationic dye carbocyanine depicting the red-shifted J band. TAs do not show any uv absorption band, and exhibition of tailing CD in the short uv region hints at its chiral conformation. Chiral conformation of TA has been confirmed from the induction of strong biphasic CD in the TA–carbocyanine system. Relative affinities for Ca2+, Mg2+, and Na+ have been probed from the disruption of metachromasia of the TA–dye system by these ions. Results show Ca2+ and Mg2+ to be almost equally effective in destroying the metachromasia of the TA–PCYN system, thus not supporting the hypothesis of special affinity for Mg2+ ion.