Hi Dr Echols,
Thank you for the suggestions. I ran the refinement again with default settings + Rigid body+ Simulated annealing (Cartesian) + Optimize X-ray/stereochemistry weight. And the statistics improved! See below:
R-work=0.2348, R-free=0.2855, Bonds=0.003, Angles=0.919.
Ramachandran outliers: 2.5%, Ramachandran favored: 88.1%.
Rotamer outliers: 10%, c-beta outliers: 0
clashscore: 9.06, overall score: 2.84
Now, I am wondering whether there is any suggestion about what to try and check next to further refine the structure. Thank you so much!