I did my simulation for protein with gromacs the result of RMSF was show flacutaions in protein structure in different area but the DSSP it does not show any change in structure. Why did this happen?
view your average structure (e.g. in VMD or PyMOL) and see if you can associate your fluctuations (you can follow by residue if your dealing with a small protein) ) with any changes in secondary structures. look for dynamic parts as Tobias suggested above