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. 2017 May 24;10:154. doi: 10.3389/fnmol.2017.00154

FIGURE 5.

FIGURE 5

Membrane-bound helical periodicity of the amphipathic motif is altered around glycine 116. (A) Continuous-wave EPR analysis of full-length wild-type CPX-1 singly labeled with MTSL at residues 110–136. Shown is the insertion depth parameter Φ, related to the ratio of accessibility to O2 and to NiEDDA as Φ = ln(ΠO2/ΠNiEDDA). Increasing Φ values indicate deeper immersion into the membrane. The blue line indicates the best fit to a cosine function with a fixed periodicity of 3.6 amino acids per turn (i.e., that expected for an ideal alpha helix). (B) Helical wheel diagram for the proposed amphipathic region of wild-type CPX-1. Residues are color coded according to their hydrophobicity as hydrophobic (black), neutral (white), polar (yellow), negatively charged (red), and positively charged (blue). The wild-type sequence does not appear amphipathic when modeled as a canonical alpha-helix. (C) Same data as shown in (A) but with residue 116 omitted. The blue line again indicates the best fit to a cosine function with a fixed periodicity of 3.6 amino acids per turn. (D) Helical wheel diagram for the proposed amphipathic region of the CTD with glycine 116 omitted. Removal of this residue results in a clear amphipathic character. Helical wheel plots were generated using the HELNET program suite (Jones et al., 1992). Gly116 is shown in bold and marked with a Δ, which also marks its location when omitted.