An evolutionarily conserved glycine-tyrosine motif forms a folding core in outer membrane proteins
Fig 9
The folding of OmpX in vivo and in vitro.
Highlighted in white spheres in both folding models are where similarities between the two folding processes may be present. In vivo: The BAM and Skp-assisted folding of OmpX into the OM. (A) OmpX is held in a flexible, relatively packed state by the Skp complex. (B) Recognition of the β-signal by the BAM complex leads to its release from Skp, and delivery to the BAM Complex. Possible interactions between the periplasmic leaflet and the β -signal and region 73–82 may also occur. (C) The BAM-assisted folding and insertion of OmpX into the OM is stabilized by the G112-Y80 motif by aligning strands 5 and 6. (D) OmpX is released from the BAM complex, and the fully-folded protein is thermally stabilized by the G112-Y80 motif. In vitro: (B) OmpX is expected to be extended in 8M urea compared to the Skp-bound form. Residual secondary structure and micelle interactions are present in the β-signal and region 73–82. (C) Upon urea dilution, OmpX will collapse and simultaneously fold into the DHPC micelle. This process is mediated by Y80G-Y112 motif, which kinetically increases the speed of folding by aligning strands 5 and 6. Strands 1 and 8 come together after folding of the protein core, followed by loop formation and a stable hydrogen bond network. (D) The final structure is thermally stabilized by the G112-Y80 motif.