We have combined electron and X-ray crystallography to study
the MlotiK1 cyclic nucleotide-regulated potassium channel. At a
first level we used electron crystallography to provide direct and
rapid turn-over information on the factors that affect crystal quality.
Crucially, the improvements in the 2D crystal quality were easily
translated into growth of high quality 3D crystals. It may be the
case that the similarities in channel packing in the 2D and 3D crystals
explain the success of this strategy. However, we suggest that
the combination of electron and X-ray crystallography could be explored
as a general approach to define more rapidly the optimal
conditions for crystal growth of membrane proteins.
We also combined electron and X-ray crystallographic information
to better understand the properties of the MlotiK1 channel.
Interestingly, the major hurdle we faced in the use of electron crystallography
was not obtaining 2D crystals but coaxing them to adhere
reliably onto grids in good form. In some instances the
handling of the crystals resulted in their disappearance or drastic
deformation. Further development or refinement of methods for
handling these very fragile samples is required.
Electron crystallography projection maps have allowed us to
uncover structural properties that are dependent on the natural
environment of the MlotiK1 channel, the phospholipid bilayer.
For example, we could only obtain crystals of MlotiK1 in the unli