page_title: Glycan-protein interactions
section_title: Binding with aromatic rings
hierarchical_section_title: Glycan-protein interactions / Binding with aromatic rings
caption_attribution_description: English: The schematic representation of CH-pi interactions including key physical characteristics: the angle from the normal (theta) and a distance from the C-atom to the plane of the ring (here, distance from C to X)
context_page_description: Glycan-Protein interactions represent a class of biological intermolecular interactions that occur between free or protein-bound glycans and their cognate binding partners. Together with protein-protein interactions, they form a mechanistic basis for many essential cell processes, especially for cell-cell interactions and host-cell interactions. For instance, SARS-CoV-2, the causative agent of COVID-19, employs its extensively glycosylated spike protein to bind to the ACE2 receptor, allowing it to enter host cells. The spike protein is a trimeric structure, with each subunit containing 22 N-glycosylation sites, making it an attractive target for vaccine search.
  Glycans, a generic name for monosaccharides and oligosaccharides, represent one of the major post-translational modification of proteins contributing to the enormous biological complexity of life. Indeed, three different hexoses could theoretically produce from 1056 to 27,648 unique trisaccharides in contrast to only 6 peptides or oligonucleotides formed from 3 amino acids or 3 nucleotides respectively.
context_section_description: The chemical intuition suggests that the glycan-binding sites may be enriched in polar amino acid residues that form non-covalent interactions, such as hydrogen bonds, with polar carbohydrates. Indeed, a statistical analysis of carbohydrate-binding pockets shows that aspartic acid and asparagine residues are present twice as often as would be predicted by chance. Surprisingly, there is an even stronger preference for aromatic amino acids: tryptophan has a 9-fold increase in prevalence, tyrosine a 3-fold one, and histidine a 2-fold increase. It has been shown that the underlying force is the  interaction between the aromatic  system and the  in carbohydrate as shown in Figure 1. The  interaction is identified if the °, the  distance (distance from  to ) is less than 4.5Å.
caption: Figure 1. The schematic representation of 
    
      
        
          C
          H
          −
          π
        
      
      {\displaystyle CH-\pi }
    
   interactions
exif: {}