In the fourth part of this series, databases (DBs) related to lectins are described. Generally, molecules that bind to glycans are called “lectins”. Lectins present in plants have been studied for a long time in biology, and are also used as a tool for investigating cells and glycans as well as for studying their physiological activities. In animal cells and in vivo, lectins such as “galectin” and “calnexin” play important roles as functional molecules that bind to glycans. Various organisms, ranging from bacteria to plants and animals, have many molecules with lectin-like activities, although most of those molecules are not known as lectins. Here, we will introduce various lectins useful for glycan research, and DBs that summarize their activities (LfDB, LM-GlycomeAtlas, MCAW-DB, and GlyCosmos Lectins).
Amylase was the first enzyme discovered, in 1833. The enzyme digests to malto-oligosaccharides or maltose from polysaccharides such as starch, and development of modified substrates and inhibitors has continued since the enzyme was discovered. Pancreatic α-amylase is synthesized by pancreas and secreted into small intestine to digest polysaccharides. We have been conducting research from a slightly different perspective than previous amylase studies as digestive enzymes, triggered by the discovery that pancreatic α-amylase binds to the N-glycan of glycoproteins. Recently, previously unknown functions of pancreatic α-amylase other than polysaccharide digestion have been discovered, such as that it determines the localization of pancreatic α-amylase in the small intestine and regulates carbohydrate digestion and absorption due to its carbohydrate-binding activity. We introduce these discoveries below.
Influenza caused by influenza A virus is one of the most widely distributed zoonotic diseases and occasionally leads to a pandemic (pdm). An influenza virus that has caused a pandemic usually becomes a seasonal influenza; however, the currently remaining seasonal viruses in human circulation are only the 1968pdm-derived H3N2 and 2009pdm-derived H1N1 variants. Influenza type A viruses have two major spike glycoproteins, hemagglutinin (HA) and neuraminidase (NA), and the viruses are further classified into subtypes that have so far been identified: H1-H18 HA subtypes and N1-N11 NA subtypes. In contrast to H17N10 and H18N11 subtypes, which have so far been found only in bats and for which sialyl sugar chains are not used for their infection, H1-H16 HA and N1-N9 NA subtypes have been found in wild waterfowls and some have been found in a variety of animals. H1-H16 HAs are responsible for the binding to sialyl sugar chains on host receptors and entry of the viral particles into host cells, whereas NAs are responsible for the hydrolysis of sialic acids (Sias) on host decoy/actual receptors to release the virus from the traps/infected cells. Sialyl sugar chains are widely distributed in animals and their chemical structures vary among animal species and tissues. Sialyl receptor binding specificity of HAs has long been studied extensively and it was found to be related to the dominant sialyl linkage type on the host target sites of influenza A viruses. The use of recently developed chemical and biological technologies and instruments has revealed the diversity of sialyl sugar receptors and/or nonsialyl receptors that are selectively used by H1-H16 HAs and that are selectively used by H17-H18 HAs. Here we review recent progress in research on receptor binding specificity of influenza A virus HAs.
