PMC

Effect of micasin on B. megaterium. (A) Killing kinetics of micasin. The cells treated with micasin or vancomycin at 5× C_L. The C_L value of vancomycin to B. megaterium is 0.119 μM, which is about twofold higher than that of micasin. Medium is without peptide. (B) Effect of micasin on bacterial membrane integrity. In each run, micasin at 5×, 10× or 20× C_L was added when the basal fluorescence remained constant for 200 s. Vancomycin and meucin-18 (C_L: 0.25 μM) were used as negative and positive control, respectively. (C) Scanning and (D) transmission electron microscopic observations of B. megaterium cells in the absence or presence of micasin. The cells were incubated with micasin at 5× C_L for 90 min at 37 °C. The particle-like materials are indicated by white arrows.

Micasin and RBD interactions. (A) Micasin is docked to the crevice of the RBD receptor−binding motif (RBM) using HEX. Micasin|A represents chain A of the complex and shown in yellow with the γ−core circled; RBD|B represents chain B with RBM engaged in interactions with ACE2 shown in green. (B) The molecular surface of RBD showing the interface occupied by micasin, with the edge colored in red. (C) Residues on RBD making contacts with micasin through hydrogen bonding and hydrophobic interactions are listed here and those also contributing to interactions with ACE2 are colored in red. (D) A hydrogen bond network on the micasin and RBD interface. The complex structure is shown as cartoons in a transparency mode in which involved residues are shown as sticks and colored in yellow for micasin and green for RBD; hydrogen bonds are shown as dashed lines in pink.

Micasin is a thermally stable CSαβ−type defensin. (A) The primary and secondary structures extracted from the structural coordinates of micasin (pdb entry 2LR5). Three disulfide bridges are indicated by lines in blue; α and β represent α−helix and β−strand, respectively. In panels A and B, two subdomains as the N−terminal helix−associated region (HAR) and the C−terminal γ−core region are shown in different colors and circled residues shaded in red and blue represent their contacts with RBD by hydrogen−bonding and hydrophobic interactions, respectively (see ). (B) The ribbon model of micasin resolved from NMR (24). The color scheme is the same as that of panel A. (C) Far−ultraviolet CD spectra of micasin after treated 0–4 days at 50 °C.

Multiple sequence alignment of malpisins. Color codes and symbol notes used here are the same as those in . Pink box indicates the N-terminus of DLPs with variable length. Sequence identity (%) to micasin is shown on the right.