Implication of an Asp residue in the ribonucleolytic activity of hirsutellin A reveals new electrostatic interactions at the active site of ribotoxins

► Most of the active site residues of ribotoxins are conserved in hirsutellin A. ► No residue in the catalytic triad is essential for the specific activity of HtA. ► D40 of HtA appears to be unique within the active site of ribotoxins. ► Spatial relationships among active site residues are crucial for optimal activity. ► There is not direct correlation between ribonucleolytic activity and cytotoxicity.