Ester protein crosslinks

Ester bonds between threonine and glutamine sidechains can form covalent cross-links between polypeptide chains. First observed in repetitive domains of a putative surface-anchored adhesin of Clostridium perfringens (Gram positive), analysis of sequences suggested "that these intramolecular ester bonds are a widespread and common feature of cell surface adhesion proteins in Gram-positive bacteria". In the examples studied, the Thr-Gln ester bonds occur between the first and last beta strands of immunoglobulin-like domains, increasing thermal stability and resisance to proteases. The structures containing such ester crosslinks "have in common is that they are very long and thin but also subject to large mechanical shear stresses and protease-rich environments".

Ester crosslinks have also been observed between serine and the carboxy termini of proteases (see examples below). These are formed autocatalytically. Similar ester crosslinks exist in proteases in which ester intermediates in the catalytic process have been trapped (see examples below).

ExamplesExamples

• 4ni6 Repeat domain 1 of Clostridium perfringens CPE0147 surface-anchored adhesin.
• 4mkm Repeat domains 1 & 2 of Clostridium perfringens CPE0147 surface-anchored adhesin.

Other Protein CrosslinksOther Protein Crosslinks

In addition to the Ester crosslinks discussed above, other covalent cross-links between polypeptide chains include:

• Disulfide bonds
• Isopeptide bonds
• Thioester protein crosslinks
• Lysine-cysteine NOS bonds