Chemical Synthesis and biological activities of chlamydial lipopolysaccharide

Research project P 13843 Chemical Synthesis and biological activities of chamydial lipolysaccharide Paul KOSMA 11.10.1999 Chlamydiae are intracellular parasitic bacteria which are -responsible for manifold acute and chronic diseases in animals and humans. Infections by C trachomatis affect 500 million people in the developing countries leading to trachoma and blindness, whereas in industrialized countries C trachomatis is most frequently diagnosed in sexually transmitted diseases. One of the most important findings of infectious disease biology in the last decade, however, has been the detection of another chlamydial species (C pneumoniae) in the context of cardiovascular diseases, most importantly with atherosclerosis. The proposed project is focussed on the chemical synthesis of one of the major antigenic determinants occurring in the outer membrane of the chlamydial cell wall. Since the highly infectious bacteria may only be grown in tissue culture, insufficient amounts of chlamydial components are available for a detailed study of their immunobiological functions. Therefore, chlamydial lipid A will be prepared by chemical synthesis and linked to the genusspecific carbohydrate epitope, which will provide chlamydial lipopolysaccharide in defined and purified form for immunobiological studies. The expected outcome should considerably improve the knowledge on the biological activities of chlamydial endotoxin, its antigenic; properties and its biosynthesis. The results may be exploited for better diagnosis of acute and chronic chlamydial infections, lead to potential vaccines or novel antimicrobials by designing proper inhibitors of glycosyl transferases in particular and prove structure -function relationships of endotoxins in general.

Chlamydiae are wide-spread bacterial intracellular parasites, which are responsible for various acute and chronic diseases. Chlamydiae cause infections of the eye leading to blindness but may also trigger urogenital infections. Moreover, these microorganisms have been found to be associated with coronary heart-diseases (arteriosclerosis, myocard-infarction), a topic of high biomedical importance. The precise role of Chlamydiae in the course of these pathological processes has not been fully clarified thus far. The components of the outer membrane, however, are implicated both in inflammatory stages and in the interaction with the immune response of the host organism. Within this project, central carbohydrate and lipid molecules derived from the chlamydial cell wall have been prepared by chemical synthesis, which are now evaluated with regard to their immunobiological properties. These molecules are otherwise only available in minute quantities by growing the highly infectious microorganisms in tissue culture. In addition, carbohydrate antigens have been synthesized which allow a diagnostic differentiation between chlamydial species. A major success has been achieved in an international cooperation by determining the three-dimensional structure of antibody-antigen complexes in the atomic detail by spectroscopic means and by x-ray crystallography. It could be shown that the antibodies are predisposed towards binding of these bacterial carbohydrate units on the genetic level. Furthermore, the crystal data allowed to rationalize the binding specificities of the antibodies, which recognize the carbohydrates in several structural variants but also in a highly specific fashion. For the first time, antibody complexes have been solved for complexes with charged sugars. The data contribute to a deepened understanding of immunological phenomena such as cross-reactivity and specific binding of carbohydrate in general. On the basis of these data, modified antibodies may be designed in the future, which might lead to the development of a protective vaccine.