I have a more general question that's come up in discussion with former colleagues: what's the largest tag that has been co-crystallized with the target protein? I'm specifically wondering about MBP - we've encountered several proteins that would express decently (and, apparently, correctly folded) with a His-MBP tag but crashed out of solution when the tag was cleaved. But I don't think anyone ever tried leaving the tag on for crystallization trials. Or what about GST?
Hey, Nat, (et. al.), Actually, I do know of one example using MBP. Jamie Williamson's lab used an MBP fusion with the L30e protein in both their crystallographic and NMR solution of its complex with RNA. Check out the following, as well as references therein: Chao JA, Williamson JR. (2004) Joint X-ray and NMR refinement of the yeast L30e-mRNA complex. Structure.2004 Jul;12(7):1165-76. Cheers, D.S.
