Substrate recognition in Bacillus anthracis sortase B beyond its canonical pentapeptide binding motif and use in sortase-mediated ligation.

Sortases are critical cysteine transpeptidases that facilitate the attachment of proteins to the cell wall in Gram-positive bacteria. These enzymes are potential targets for novel antibiotic development, and versatile tools in protein engineering applications. There are six classes of sortases recognized, yet class A sortases (SrtA) are the most widely studied and utilized.

Structures of Streptococcus pyogenes class A sortase in complex with substrate and product mimics provide key details of target recognition.

The cell wall is a critical extracellular barrier for bacteria and many other organisms. In bacteria, this structural layer consists of peptidoglycan, which maintains cell shape and structural integrity and provides a scaffold for displaying various protein factors. To attach proteins to the cell wall, Gram-positive bacteria utilize sortase enzymes, which are cysteine transpeptidases that recognize and cleave a specific sorting signal, followed by ligation of the sorting signal-containing protein to the peptidoglycan precursor lipid II (LII).