Solution-NMR characterization of outer-membrane protein A from E. coli in lipid bilayer nanodiscs and detergent micelles.

ABSTRACT: X-ray crystallography and solution NMR of detergent-reconstituted OmpA (outer membrane protein A from E. coli) had shown that this protein forms an eight-stranded transmembrane ?-barrel, but only limited information was obtained for the extracellular loops. In NMR studies of OmpA in two different detergent micelles, "NMR-invisible" amino acid residues in-between the extracellular loops and the ?-barrel prevented complete structural characterization. Here, we show that this NMR-invisible ring around the ?-barrel of OmpA is also present in lipid bilayer nanodiscs and in mixed micelles with a third detergent, thus suggesting that the implicated rate processes have a functional role rather than representing an artifact of the protein reconstitution. In addition to sequence-specific NMR assignments for OmpA in the nanodiscs, the present results are based on a protocol of micro-coil TROSY- and CRINEPT-type NMR diffusion measurements for studying the hydrodynamic properties and the foldedness of [(2)H,(15)N]-labeled membrane proteins in nanodiscs. This protocol can be applied under conditions closely similar to those used for NMR structure determinations or crystallization trials.

SUBMITTER: Susac L 

PROVIDER: S-EPMC4105301 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature