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. 2019 Jul 16;117(4):751–766. doi: 10.1016/j.bpj.2019.07.011

Figure 2.

Figure 2

Folding KvAP at the solid-liquid interface. (A) The xSLD(z) profile for a KvAP-DM monolayer tethered to the surface of an Si-Ge-Si multilayer substrate is shown. The horizontal dashed lines above and below the abscissa were used to estimate the propagation of errors. (B) The xSLD(z) profiles for an Si-Ge-Si multilayer substrate with only the organic SAM used to tether the KvAP-DM monolayer to its surface (dashed) and for a slightly different Si-Ge-Si multilayer substrate with a KvAP-DM monolayer tethered to its surface (solid) are shown. The xSLD profiles for the multilayer substrates occur for z < 0 Å, whereas those for the SAM or tethered KvAP-DM monolayer occur for z > 0 Å. (C) The xSLD(z) profile for the tethered KvAP-DM monolayer (solid) with estimated errors is shown, compared with the xSLD(z) profile calculated from the x-ray crystal structure for KvAP-DM (dashed). (D) The xSLD(z) profile for the KvAP-POPC membrane after POPC-DM exchange (gray with estimated errors) is shown, compared with the xSLD(z) profiles calculated for the model proposed for KvAP (gray solid) within a phospholipid bilayer environment described in (E), as well as for rotations of 5° (dotted), 10° (black solid), 15° (dashed), and 20° (dash-dot) less than the 90° originally proposed. (E) An illustration is given showing the proposed (31) refolding of the S1 helix to form a four-helix bundle structure for the VSDs and reorientation of the bundle axis relative to the pore axis of KvAP via a rotation of ∼90° upon the transformation from a detergent micelle environment (left side) to a phospholipid bilayer environment (right side). One VSD is shown in the foreground (black) with the PD in the background (gray). (F) Top view and side view (of one subunit) of the 3-D structure proposed for KvAP in a phospholipid bilayer environment from (31) is shown in a ribbon representation (gray), compared with that for a rotation of the VSDs by 10° less (black) than originally proposed. The xSLD(z) profiles are in units of electron density, e−/Å3.