Abstract
A number of studies have shown that glycosylation of proteins plays diverse functions in the lives of organisms, has crucial biological and physiological roles in pathogen–host interactions, and is involved in a large number of biological events in the immune system, and in virus and bacteria recognition. The large amount of scientific interest in glycoproteins of molluscan hemocyanins is due not only to their complex quaternary structures, but also to the great diversity of their oligosaccharide structures with a high carbohydrate content (2–9%). This great variety is due to their specific monosaccharide composition and different side chain composition. The determination of glycans and glycopeptides was performed with the most commonly used methods for the analysis of biomolecules, including peptides and proteins, including Matrix Assisted Laser Desorption/Ionisation–Time of Flight (MALDI-TOF-TOF), Liquid Chromatography - Electrospray Ionization-Mass Spectrometry (LC/ESI-MS), Liquid Chromatography (LC-Q-trap-MS/MS) or Nano- Electrospray Ionization-Mass Spectrometry (nano-ESI-MS) and others. The molluscan hemocyanins have complex carbohydrate structures with predominant N-linked glycans. Of interest are identified structures with methylated hexoses and xyloses arranged at different positions in the carbohydrate moieties of molluscan hemocyanins. Novel acidic glycan structures with specific glycosylation positions, e.g., hemocyanins that enable a deeper insight into the glycosylation process, were observed in Rapana venosa, Helix lucorum, and Haliotis tuberculata. Recent studies demonstrate that glycosylation plays a crucial physiological role in the immunostimulatory and therapeutic effect of glycoproteins. The remarkable diversity of hemocyanin glycan content is an important feature of their immune function and provides a new concept in the antibody–antigen interaction through clustered carbohydrate epitopes.
Highlights
Glycoproteins are of great importance for the optimal and proper functioning of many bioactivities in the human body
They have been compared with the well-studied oligosaccharide structure of keyhole limpet hemocyanin (KLH) from a mussel inhabiting the northern coast of America, and other hemocyanins with complex carbohydrate structures
Similar structures have been published for other molluscan hemocyanins, such as Helix pomatia, Lymnaea stagnalis [16], and Arion lusitanicus [19], suggesting that methylated N-glycans perform an important function in the body
Summary
Glycoproteins are of great importance for the optimal and proper functioning of many bioactivities in the human body. Molluscan hemocyanins are among the largest known glycoproteins with huge cylindrical multimeric forms and molecular masses ranging from 3.3 to 13.5 MDa. Molluscan hemocyanins are among the largest known glycoproteins with huge cylindrical multimeric forms and molecular masses ranging from 3.3 to 13.5 MDa They form decamers or multi-decamers of 330- to 550-kDa subunits organised by more than seven different functional units (FUs) with molecular masses ranging from 45 to 65 kDa. Structural subunits assemble to di-decamers as presented for keyhole limpet hemocyanin (KLH1) in (Figure 1) [7]. The represented X-ray crystal structure of the intact 3.8-MDa molecule of Todarodes pacificus squamous hemocyanin (TpH) shows the complex oligosaccharide structures of the glycoprotein [8]. The studies on carbohydrate structures of hemocyanins from molluscs occupy an important part of this review, demonstrating significant differences in carbohydrate structures of molluscan hemocyanins
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