Abstract
Escherichia coli K1 secretes a homopolymer capsular polysaccharide (CPS) consisting of alpha 2, 8 linked N-acetylneuraminic acid (poly alpha 2,8NeuNAc). Typically poly alpha 2,8NeuNAc is arranged in low and high order alpha helices with carboxyl and hydroxyl groups extending from the helices. Several properties of CPS such as antigenicity and metal binding can be influenced by its structural conformation. We examined the influences of metal ions and temperature on the secondary structure of poly alpha 2,8NeuNAc. Conformation alteration was detected by ultraviolet (UV) spectroscopy and circular dichroism (CD). The majority of metal ions tested had no detectable influence on poly alpha 2,8NeuNAc structure. In contrast, Yb3+, Hg2+, and Cu2+ ions greatly altered the UV and CD spectra, which suggests that these ions had disrupted the alpha helical structure of poly alpha 2,8NeuNAc. These changes were influenced by the metal ion concentration. When poly alpha 2,8NeuNAc was incubated at temperatures ranging from 20-60 degrees C, alterations in its UV absorption spectra were also seen. The most significant change occurred between 35 and 40 degrees C. In summary, this study suggests that the higher order structure and function of bacterial CPS may be influenced by environmental factors.