Physiological Significance of Animal-and Tissue-specific Sialic Acid Composition

Sialic acids serve as targets for various molecular recognition events because of their location at the terminous of glycans and because they exhibit a variety of structures by various molecular modifications. Focusing on modification at the C-5 position, sialic acids in mammals are mainly categorized in two groups, N-acetylneuraminic acid and N-glycolylneuraminic acid (Neu5Gc). The ratio of these two forms varies among tissues and between animal species. There are two interesting features in Neu5Gc expression; Neu5Gc is absent in the brain of all vertebrates and absent in all human tissues. However, the physiological significance of these specific expression patterns of Neu5Gc is largely unknown. Several model mice with perturbed Neu5Gc expression were established and studies using these mice reveal that the lack of Neu5Gc is involved in some pathological conditions of human-specific diseases.