Lipid glycosylation: a primer for histochemists and cell biologists

Abstract

Glycolipids are glycoconjugates that are predominantly found on the extracellular surface of cells ranging from bacteria to men. In bacteria and plants, glycoglycerolipids represent the main glycolipid species. Ceramides as carrier for glycans, termed glycosphingolipids (GSLs), are characteristic for vertebrates and insects. The glycan part is involved in a variety of biological activities including cell adhesion and initiation of signaling. Most of these functions rest on two basic principles: (1) GSLs spontaneously contribute to organize lipid rafts in biological membranes, thereby forming functional complexes ('glycosynapses') with receptor proteins and ion channels and (2) their glycans are bound by receptors like galectins (protein-glycan recognition) or cognate glycans (glycan-glycan recognition). This interaction modulates cell adhesion, differentiation and growth processes. Besides their contribution to normal cell behavior, GSL expression patterns also influence disease processes by inducing cellular malfunctions when aberrant, as highlighted by inherited disorders of GSL metabolism like sphingolipidoses. Altered GSL patterns are also associated with common neurological diseases, autoimmune diseases and cancer. With respect to infections, various GSL-presented glycans are attachment sites for bacteria and viruses as well as primary targets for bacterial toxins. This review provides an introduction to GSL structures, their nomenclature and metabolism. Building on this, normal and pathological functions of GSL will be surveyed.

Sialylation of N-glycans: mechanism, cellular compartmentalization and function

“…Interestingly, the ability of NEU3 to convert GT1b and GD1a to monosialic GM1 plays a role in axon growth and regeneration (reviewed in (Higuero et al 2017) in this issue). See also the article by Kopitz (2017) in this issue for more information on glycolipids and the article by Kaltner et al (2017) in this issue on the functional consequences of galectin binding to glycolipids once Sia is removed. Two isoforms of NEU4 have been reported, and they are believed to direct the localization of NEU4 to lysosomes, mitochondria or the ER in different tissues.…”

Membrane assembly of Shiga toxin glycosphingolipid receptors and toxin refractiveness of MDCK II epithelial cells

“…Glycosphingolipids (GSLs) belong to the structurally very diverse group of sphingolipids (1-3) and are not just structural elements of cells but also participate in intra-and extracellular signaling (4)(5)(6)(7)(8)(9)(10).…”

The emerging role of galectins in (re)myelination and its potential for developing new approaches to treat multiple sclerosis

“…In terms of a recognition process of broad relevance, the abundance of glycoconjugates in the nervous system directs attention to considering the glycan part of glycolipids and glycoproteins as versatile ligand (for introduction into these glycan structures, please see [24][25][26][27][28][29][30][31]). In fact, the concept of the sugar code assigns an unsurpassed ability to store information to these glycans.…”