I have solved a structure of a glucose binding protein of CE4 family. When I try to solve the structure using the same CE4 family enzyme as search model, it failed for many case. Finally, I solved the with a same family enzyme used as search model. As soon as I solved the structure, I superposed my final refined model with structures of CE4 family enzymes which did not produce the good molecular replacement solution for my enzyme. I found that all are having (Beta/alpha)7 fold and superpose very well with my model. Whereas, some loop region are not superpose very well. My doubt is why molecular replacement failed thought over-all fold is same?.