Hydrogen bond plays an important role in stability, dynamics and function of protein. Most of backbone hydrogen bonds are well wrapped by nonpolar groups of side chains. However, there are a small portion of hydrogen bonds vulnerable to water attack. Those under-wrapped hydrogen bonds, termed as "dehydron", are sensitive to the change in the local electrostatic environment. Dehydrons constitute a hot spot for protein interactions. They have been identified as structural marker for protein association, proteamic connectivity and protein-ligand binding. The effects of dehydrons on protein hydration shell are assessed by studying the mobility of hydration water. Calculation of water residence times of all residues reveals that dehydrons enhance the water mobility and promote the most intense loosening of hydration shell. Targeting loose hydration shells induced by dehydrons provides a powerful strategy in rational drug design.