Membrane proteins and large protein complexes are notoriously difficult to study with X-ray crystallography, not least because they are often very difficult, if not impossible, to crystallize, but also because their very nature means they are highly flexible. The result is that when a structure can be obtained it is often of low resolution, ambiguous and reveals a mosaic-like spread of protein domains that sometimes create more puzzles than they solve. [Schröder, Levitt & Brunger. (2014), Acta Cryst. D70, 2241-2255; doi: 10.1107/S1399004714016496 ]
