Gerardy-Schahn, Rita
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Gerardy-Schahn, Rita
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Gerardy-Schahn, Rita
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Item type:Publication, The evolutionary history of sialylation - Perspectives from fish genomes(2004-07-21); ; ; Sialic acids are key determinants of carbohydrate structures that play important roles in a variety of biological functions. In order to obtain a better understanding how sialylation developed during evolution we investigated two completely sequenced teleost genomes (Takifugu rubripes and Danio rerio) with emphasis on the proteins involved in biosynthesis and recognition of sialic acids. The analysis revealed the existence of all key enzymes crucial for sialic acid metabolism including putative orthologues for almost all 20 sialyltransferases (STs) known for mammalian species. A thorough phylogenetic analysis of all ST sequences has provided strong evidence that the development of the major ST branches occurred well before the diversification into protostomes and deuterostomes strongly suggesting that the defining characteristics of STs have not changed much in 1000 million years. Interestingly, from the relationship between the ST subfamilies it can be deduced that the evolution of the different ST lineages was driven by the availability of appropriate acceptor substrates.In contrast to STs, the largest family of sialic acid-recognizing lectins found in mammals, the siglecs, seems to be a relatively new invention in evolution. Analysis of the two teleost genomes revealed only one unambiguous orthologue of the known mammalian siglecs showing highest sequence similarity to mammalian Siglec-4, the myelin-associated glycoprotein (MAG). Although the low sequence similarity in the cytoplasmic tail, different splice variants and the existence of several motifs implicated in signal transduction suggest alternative biological functions for this part of the protein, the high conservation of genomic organization, binding specificity and expression of Siglec-4 from fish to mammals emphasizes an indispensable role for this protein in all vertebrates in contrast to other Siglecs which maintained a high degree of structural and possibly functional flexibility during evolution.doctoral thesis261 160 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Structure and Function Relationship of Trans-Sialidases from Trypanosoma congolense(2015-11-13); ; ; The study presented here addresses structural and functional relations of trans-sialidases (TS) from the African parasite Trypanosoma congolense and their biochemical characterisation. TS are unusual enzymes found in the flagellate protozoan parasite Trypanosoma and catalyse the stereo and region specific transfer of terminal sialic acid from donor sialo-glycoconjugates to terminal galactose residues of suitable acceptor substrates, resulting in alpha-2,3-sialylated glycoconjugates. Major research on trypanosomal TS has been done on Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. However, only little has been known about TS from the African Trypanosoma congolense TS, the prevalent causative agent of African animal Trypanosomiasis (AAT) in livestock and domestic animals also termed nagana.doctoral thesis376 374