An atomic-force basis for the bacteriolytic effects of granulysin.

While granulysin has been suggested to play an important role in adaptive immune responses against bacterial infections by killing pathogens, and molecular force for protein-protein interaction or protein-bacteria interaction may designate the specific functions of a protein, the molecular-force basis underlying the bacteriolytic effects of granulysin at single-molecule level remains unknown. Here, we produced and purified bactericidal domain of macaque granulysin (GNL). Our bacterial lysis assays suggested that GNL could efficiently kill bacteria such as Listeria monocytogenes. Furthermore, we found that the interaction force between GNL and L. monocytogenes measured by an atomic force microscopy (AFM) was about 22.5 pN. Importantly, our AFM-based single molecular analysis suggested that granulysin might lyse the bacteria not only through electrostatic interactions but also by hydrogen bonding and van der Waals interaction. Thus, this work provides a previous unknown mechanism for bacteriolytic effects of granulysin.