Thioester bonds between cysteine and glutamine sidechains can form covalent cross-links between polypeptide chains. An accurate estimate of the number of thioester bonds in the PDB may not be available (see Protein crosslinks#Thioester Crosslinks). A search for "thioester" in Proteopedia yields >500 hits.
- Thioester bonds in complement proteins C3 and C4 are involved in tagging pathogens for destruction by the immune system, via the alternate complement activation pathway. Example: 2b39.
- Thioester bonds occur in thioester domains (TED) of Gram-positive bacteria, where they are thought to mediate covalent adhesion of bacteria to host cells[1][2], or to participate in bacterial conjugation involved in antibiotic resistance[3]. Many surface proteins of Gram-positive bacteria are predicted to contain TED as well as isopeptide and ester cross-links. This family of proteins is termed TIE proteins for thioester, isopeptide, ester proteins[2]. Examples: 2xi9, 6fwy.
- In a dramatic example, the pilus tip adhesin of Streptococcus pyogenes forms dimers in the presence of spermidine, a di-amine that forms thiopeptide bonds with the Gln211 residues in two adhesin protein chains, illustrated in 4c0z[4].
