Dear Gerard and James, Thank you very much for the suggestions. My data was collected at APS. Yesterday, an expert in my institution kindly inspected my raw data and pointed out to me that my data are indeed severely anisotropic in the b direction. He also recommended me to cut the data to 3.27 A (or lower). I took his advise and tried refining the data with a resolution of 3.27 A. I found that it indeed reduced the values of Rwork/Rfree too much more reasonable window (0.264/0.322, respectively). I will try improving the quality of my crystals and hope to collect better data sets.
I am a new comer to protein crystallography. I appreciate all for giving me valuable advises. Sincerely, Khoa Pham
