Returning to the previous discussion, we've had luck crystallizing several proteins with a His-tag. We've used both N-terminal and C-terminal his tags, and have had success with both of them. In one of our structures, the his tag actually formed an interface for crystal packing.
We have also tried using the "Tagzyme" kit to remove the tags of our proteins that were not crystallizing. We found that cleavage of the His-tag with Tagzyme was very unsuccessful for our proteins. Kathleen
