Sialic acids, sialoconjugates and enzymes of their metabolism in fungi

Abstract

Sialic acids (Sia) represent a set of derivatives of nine-carbon sugar neuraminic acid that occupy a terminal position in oligosaccharide chains located on the surface of cells. They are very important for several physiological and pathological processes, including bacterial and viral infections. Until recently, Sia had been described mostly in animals, viruses, bacteria and protozoan species. In the last years, information on sialic acids existence in filamentous fungi has been published, but these data are very scarce. The same is valid for the enzymes that are involved in the synthesis, transport and degradation of Sia in fungi. So far, most data known regarding fungal sialidases are a result of published complete fungal genomes. However, based on the accumulated data, it appears that the kingdom of fungi probably harbours hitherto unknown mechanisms and enzymes of sialic acid metabolism. This review attempts to present the state of knowledge on sialic acids in fungi with respect to their structure, diversity and biological role, as well as Sia metabolism and enzymes involved in their conversion. The summary is presented at the background of the respective metabolic mechanisms possessed by eukaryotes and prokaryotes. The possible role of sialome and sialometabolism in fungi are also discussed.