Fig 1.
Structure comparison of MAP30 and Momordin.
(A) MAP30 and (B) Momordin as viewed towards their respective active-sites, with key residues discussed in the text highlighted as follows: catalytic-site (green), Mn+2-binding site (yellow), and on the active-site-distal face, the ribosome-binding site (cyan) with the c11-P peptide-interacting Tyr residue (magenta). (C) Sequence alignment of MAP30 and Momordin with residues highlighted as above. Note that the structures for both MAP30 (PDB: 1D8V, 1CF5) and Momordin (PDB: 1MOM, 1AHA) are all missing 23 N-terminal residues. The C-terminal 19 residues are shown in the nuclear magnetic resonance structure of MAP30 (PDB: 1D8V) but not in the X-ray crystal structures of either protein. The N-terminal residues were missing, and C-terminal residues were present, on both proteins employed here.
Fig 2.
SARS-CoV-2 inhibition by MAP30 and Momordin.
Viral inhibition and cell viability as a function of concentration of MAP30 and Momordin, either without (A and B) or with (C and D) a C-terminally appended Tat cell penetration peptide, as assessed in the A549 NLRV assay. The results from this and other assays are summarized in Table 1.
Table 1.
Viral inhibition and cytotoxicity values of MAP30 and Momordin.
Fig 3.
Assessment of SARS-CoV-2 inhibition by MAP30, MAP30.Y70A, and MAP30.K171, K215 in the A549 NLRV assay. The Y70A active-site mutation abrogates both viral inhibition and cytotoxicity. The MAP30.K171, K215 ribosome-binding-site mutations result in an increase of both the IC50 and CC50 values, while the selectivity index (SI = CC50/IC50) remains the same.
Fig 4.
Comparison of MAP30 and Momordin active-site faces.
(A-C) MAP30, TCS, and Momordin represented as hydrophobicity surfaces (blue, charged; orange, hydrophobic; white, neutral), (D-F) as charge surfaces (blue, basic; red, acidic; white, neutral), and (G-I) with residues scored as important by Evolutionary Trace shown in red. PDB codes and percent sequence identity to MAP30 as indicated. Ricin (PDB: 1APG, 30.5%) and Saporin (PDB: 1QI7, 23.5%) gave similar patterns (not shown). The binding groove with the catalytic site at the center is located between the two arrows in (A). The regions of the previously identified Mn+2 and Zn+2 binding areas are indicated in (D).
Fig 5.
Comparison of MAP30 and Momordin ribosome-binding-site faces.
(A-C) MAP30, TCS, and Momordin represented as hydrophobicity surfaces (blue, charged; orange, hydrophobic; white, neutral), (D-F) as charge surfaces (blue, basic; red, acidic; white, neutral), and (G-I) with residues scored as important by Evolutionary Trace shown in red. PDB codes and percent sequence identity to MAP30 as indicated. Ricin (PDB: 1APG, 30.5%) and Saporin (PDB: 1QI7, 23.5%) gave similar patterns (not shown). The c11-P peptide bound to TCS, and aligned to MAP30 and Momordin, is shown in magenta. The C-terminal end of the peptide is bound in a hydrophobic groove common to all the proteins (A-C) and the N-terminal end, with acidic resides D2, D3, and D4 (indicated by the arrow in D), likely interacts with a basic region on MAP30 but not the corresponding acidic region on Momordin (D and F). The hydrophobic groove (indicated by a dashed arrow in G), and particularly Y164 in MAP30 and Y166 in Momordin, appear to be important (G and I).