Raman spectroscopy of sialic acids. Spectral bands of α-(2→3)- and α-(2→6)- sialyl linkages of oligosaccharides

Abstract

The occurrence of a.2~3 and a.2~6 linkages in different complex carbohydrates has raised the question of glycosidic linkage specificity of the sialidases [1]. Sialyloligosaccharide moieties of cell-surface glycoproteins and glycolipids exhibit significant structural diversity, and ability of sialic acid to serve as a receptor detenninant of viruses depends on the carbohydrate structure of sialylglycoprotein, ganglioside, or sialyloligosaccharide. Particulary, it was shown that the ability of influenza viruses to binding with cell-surface glycans is differentiated between the Neu5Aca.2~3Gal-and Neu5Aca.2~6Gal-tenninated sequences, while role of more distant carbohydrate parts of the receptor is poorly defined [2]. The increased expression of a.2~3-linked sialic acid which occurs for acute-phase protein transferrin in cancer and for a.1-acid glycoprotein in liver cirrhosis was also found [3].In the present study, we used Raman scattering spectroscopy for the detennination of the type of linkage (a.2~3 or a.2~6) of sialic acid residues to cabohydrate units of glycoconjugates. Raman spectra of aqua solution of tri-saccharides (Fig. 1 ) Neu5Aca.2~3Galf3I-44Glc and Neu5Aca.2~6Galf3I-44Glc were analyzed. Significant differences in the regions 400-800 cm-I of Raman spectra of these tri-saccharides were observed. There are some additional lines, such as at 572, 620, 707 and 754 cm-I , in the Raman spectrum of Neu5Aca.2~6Galf3I~4Glc. The intensity of line at 440 em-I is increased in the spectrum of Neu5Aca.2~3Galf3I-44Glc in comparison with the spectrum ofNeu5Aca.2~6Galf3I-44Glc.Normal coordinate calculations for the Neu5Aca.2~6Gal and Neu5Aca.2~6Gal fragments show that the line at 440 cm-I is arisen from COC symmetric deformation of the a.2~3 glycoside bond. In the case of a.2~6 glycoside bond, the eoe vibration mixes with CCC and oce deformations and to some extent with ee stretching. In particular, the eoe symmetric deformation contributes only 11-12% of the potential energy of vibrations 572, 620 and 754 cm-I ; the CO stretching gives 28% in 620 em-I and 7% in 707 em-I vibrations; the ee stretching of a.2~6 glycoside chain -6% in 572 and 620 cm-I , and 11 % of potential energy in 754 cm-I vibrations. The carbon and oxygen atoms nearest to glycosidic bond between the sialic and galactose moieties give significant contribution to potential energy of these vibrations.

Raman Microscopy Analysis of the Biochemical Changes in the Cytoplasm of Bovine Oocytes Induced by an In Vitro Maturation Process: Interference of the Zona Pellucida

“…According to the vast literature concerning the protein AmI band, components at 1693, 1676, 1663, and 1651 cm −1 were assigned to turns, β‐sheet, random coil, and α‐helix protein conformations, respectively. The stronger component, centred at 1656 cm −1 , was attributed to the C=C stretching of unsaturated lipid,, while that at 1639 cm −1 , clearly observed as a well‐defined shoulder in the IMM−E‐ZP contour, was assigned to the AmI mode of carbohydrates containing the N‐acetyl substituent ,. The band at 1621 cm −1 was assigned to Tyr ring stretching .…”