When one considers the interplay between spontaneous and explicit symmetry breaking in finite charge density systems, one can observe the metal-insulator phase transition when the spontaneous superstructure is formed on top of the explicitly broken state. This goes under the name of "pinning of charge density wave" and eventually can lead to the formation of a Mott insulator, when the pinning gets strong. I will discuss the examples of this phenomenon in holographic models with periodic inhomogeneous and helical homogeneous lattices. The insulating state formed in these holographic models turns out to be quite interesting: firstly it is gapless and inherits the scaling features of the near horizon geometry; secondly, it demonstrates strong suppression of conductivity even for weak explicit translational symmetry breaking, which goes beyond the usual picture of the conductivity being governed by the momentum relaxation rate.