In proteins, aromatic amino acid side chains are often engaged in noncovalent π interactions such as π–π, cation−π, and CH−π interactions contributing to protein stability, protein–ligand interactions, catalysis, and self-assembly. Tryptophan (Trp) holds a unique place in biology for a multitude of reasons. It is the largest of all twenty amino acids in the translational toolbox. Its side chain is indole, which is aromatic with a binuclear ring structure, whereas those of Phe, Tyr, and His are single-ring aromatics. In part due to these elaborate structural features, the biosynthetic pathway of Trp is the most complex and the most energy-consuming among all amino acids. Essential in the animal diet, Trp is also the least abundant amino acid in the cell, and one of the rarest in the proteome. In most eukaryotes, Trp is the only amino acid besides Met, which is coded for by a single codon, namely UGG. Due to the large and hydrophobic π-electron surface area, its aromatic side chain interacts with multiple other side chains in the protein, befitting its strategic locations in the protein structure. Here you can see an example showing how a Tryptophan residue is use to stabilize a protein-protein interaction, exemplified by the crystal structure of NS2B-NS3 protease from Zika Virus (PDB code: 7H25)

#protein #interaction #molecularart #tryptophan #zika #virus #complex

Structure rendered with @proteinimaging, post-processed with @stylar.ai_official and depicted with @corelphotopaint