Cation- interaction (represented as yellow cone) between side chain of Lys4 of Mtb GS carrying net positive charge and aromatic rings of PA. (a) Simultaneous formation of H-bond (represented as green dotted line) is observed between -NH2 group of Lys4 of Mtb GS and O-atom at C-7 position of DAMC; (b) interaction of 7-AMC with crystal structure of Mtb GS; (c) interaction of 7-NH-AMC with the crystal structure of Mtb GS. Cation- interaction occurs when the distance between a positively ionisable atom and the centroid of an aromatic ring is equal to or less than 4.0 , and the angle between the normal vector of the plane and the vector between the ionisable atom and the centroid is equal to or greater than 45° and less than 90° [30]. All the three interactions are in the permissible limits of the cation- interaction (as labeled in the figure).