The compressibility effects on the evolution of mixing layers are characterized using flow topology, which is classified according to the Q-criterion. Conditional statistical analysis of DNS data shows that strain-dominated regions are more effective in the redistribution of turbulent stresses and hence, produce more turbulent kinetic energy than vortex-dominated regions. As compressibility effects increase, the vortex-dominated fraction of the flow field increases, resulting in an overall suppression of turbulence. Further, we establish a relation between turbulent energy production and orientation of helical streamlines, which are observed in the neighborhood of vortex-dominated regions. Vortex vectors are used to describe the orientation of these vortical structures and streamlines. With increasing Mach number, the vortical structures become more aligned in the streamwise direction. Such streamlines are associated with lower values of energy production. Thus, the change in orientation of the vortical structures or helical streamlines directly reflects the suppression of turbulent kinetic energy production by compressibility.