Crystallizing transmembrane peptides in lipidic mesophases

Abstract

Structure determination of membrane proteins by crystallographic means has been facilitated by crystallization in lipidic mesophases. It has been suggested, however, that this so-called in meso method, as originally implemented, would not apply to small protein targets having </=4 transmembrane crossings. In our study, the hypothesis that the inherent flexibility of the mesophase would enable crystallogenesis of small proteins was tested using a transmembrane pentadecapeptide, linear gramicidin, which produced structure-grade crystals. This result suggests that the in meso method should be considered as a viable means for high-resolution structure determination of integral membrane peptides, many of which are predicted to be coded for in the human genome.

Figure 1

Cartoon representation of the events proposed to take place during the crystallization of linear gramicidin from the lipidic cubic mesophase. Lollipop-shaped objects represent the lipid monoolein, gramicidin dimers are colored purple, and the aqueous medium is shaded blue. See text for details. Adapted from Cherezov et al. (4).

Figure 2

Structure of gramicidin obtained using crystals grown in meso. (A and C) Molecular structures of intertwined gramicidin dimers and (D–F) crystal packing arrangement. Alternate layers in panels D and E are colored red and blue to highlight Type I packing. Individual monomers in panels A and C are colored red and blue for clarity. (B) Crystals of gramicidin growing in meso (scale bar, 80 μm).