Crystallization of Escherichia coli maltoporin in the trigonal space group R3

Maltoporin is an outer-membrane protein that forms a β-barrel composed of three monomers and ensures the transport of maltose and maltodextrin in Gram-negative bacteria. Previously, the crystallization of Escherichia coli or Salmonella typhimurium maltoporin has been achieved in the presence of a mixture of the detergents β-decylmaltoside and dodecyl nonaoxyethylene. These crystals all belonged to the orthorhombic space group C222₁ and gave rise to several structures of maltoporin in complex with different carbohydrates determined at resolutions between 3.2 and 2.4 Å. Here, the crystallization of E. coli maltoporin in a new crystal form is reported; the crystals belonged to the trigonal R3 space group and diffracted to 1.9 Å resolution. These crystals were obtained using n-dodecyl-β-D-maltoside as a detergent. Crystals with a lens or pyramidal morphology could be obtained using sitting or hanging drops, respectively, and despite their very different shapes they presented the same space group and very similar unit-cell parameters.