# Role of Protein Glycoslation in Host-Pathogen Interaction
## 7 Lectin, a Class of Protein Entangled with Glycoprotein, Affects Host-Pathogen Interactions
### Pathogen Lectins  
Pathogen lectins usually promote infection by sensing hosts or suppressing host immunity. Host recognition is the prerequisite of a successful pathogen infection [193]. This process is affected by a variety of factors, among which lectins on the surface of pathogens and glycans on the surface of host cells (\(N\)-linked or \(O\)-linked carbohydrate residues of glycolipids or glycoproteins) are crucial [194]. One typical example is the Influenza Virus (IAVs) surface glycoprotein haemagglutinin (HA). It is a trimeric lectin in IAVs that can help host recognition and further cytoplasm penetration through binding SA-containing glycoproteins on host cell membranes [195; 196]. The subtypes of IAVs vary in host ranges depend on specific host recognition of HA [197], especially the differences in the glycosidic bonds of penultimate carbohydrate of the SA residue [198; 199]. In avian respiratory epidermal cells, the linkage of penultimate carbohydrate of the SA residues is \(\alpha\)-2,3 glycosidic bonds, while it is \(\alpha\)-2,6 glycosidic bonds in human [200]. Based on amino acid sequences in the HA sugar-binding domain, avian-adapted IAVs preferentially bind \(\alpha\)-2,3-SA while it is \(\alpha\)-2,6-SA for human-adapted IAVs [201; 202]. Another example is the gram-negative bacterium _Pseudomonas aeruginosa_, which can cause various diseases in humans, such as bacteremia, chronic pulmonary infection, urinary tract infection and acute ulcerative keratitis. It has two lectins, LecA and LecB, respectively binding the galactose and fucose residues of glycoconjugates on epithelial cells of various tissues. With these two lectins, _P. aeruginosa_ can recognize and infect the lung or other host cell tissues [32]. Another gram-negative bacterium, _H. pylori_ that causes gastritis, stomach ulcers, and stomach cancer, has different lectins on the cell surfaces [203; 204]. These lectins recognize the carbohydrate residues on the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Family**} & **Subcellular** & **Carboux-Binding** & **Main Function** & **Reference** \\  & **Localization** & **Specificity** & & \\ \hline \multirow{3}{*}{Hevein} & \multirow{3}{*}{Vacuolar, cell wall} & Chito-oligosaccharides, high & \multirow{3}{*}{Anti phytophagous and/or \(N\)-glycans, \(N\)-acetyl-b-glucosamine} & \multirow{3}{*}{Anti phytorous animals} & [161; 169] \\  & & & & \\ \cline{3-4}  & & & & \\ \hline \multirow{3}{*}{Jacalins} & Nucleus, cytoplasm, vacuole & \multirow{3}{*}{Mannose, galactose} & Development and defense & \multirow{3}{*}{[172; 173; 174; 175]} \\  & & & & \\ \hline \multirow{3}{*}{Legume lectin} & Extracellular, cytoplasm, vacuolar & \multirow{3}{*}{Sialic acid, mannose, \(N\)-acetylgalactosamine, \(\text{defense}\) response} & Anti phytophagous and/or \(N\)-acetyl/galactosamine, \(\text{defense}\) response & \multirow{3}{*}{[176; 177; 178; 179]} \\  & & & & \\ \hline \multirow{3}{*}{Lysin domain} & Cell membrane, vacuolar & \multirow{3}{*}{\(N\)-acetyl-b-glucosamine} & Perception and recognition & \multirow{3}{*}{[21; 180; 181; 182; 183]} \\  & & & & \\ \hline \multirow{3}{*}{Nictaba} & Nucleus, cytoplasm, & \multirow{3}{*}{\(N\)-acetyllactosamine, \(N\)-acetylaceous, high- mannose \(N\)-glycans} & Anti phytophagous and/or \(N\)-acetyl-b-glucose & \multirow{3}{*}{[184; 185; 186]} \\  & & & & \\ \hline \multirow{3}{*}{Ricin-B family} & Nucleus, cytoplasm, vacuolar & Gal, GalNAc, glycans & Anti phytophagous and/or \(N\)-acetyl-b-glucose & \multirow{3}{*}{[187; 188]} \\  & & & contain sialic acid & herbivorous animals \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._cell surface of the gastric mucosa to mediate _H. pylori_ infection. Among several lectins in _H. pylori_ outer membrane, the blood group antigen-binding adhesin (BabA) and the lacdiNAc-binding adhesin (LabA) are well studied.