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Figure 3
Structure of an MBP-SpsB–inhibitor peptide complex. Cartoon diagram showing the overall structure of a representative MBP-SpsB–inhibitor peptide complex. MBP is coloured cyan, SpsB green and the peptide blue. The three-amino-acid linker (Ala-Gly-Ala) between MBP and SpsB is shown in red and the engineered thiol group (MBP Q78C) in yellow (marked with an asterisk). Shown in stick form (green), adjacent to the peptide, are the SpsB catalytic residues Ser36 and Lys77. The N- and C-­termini of the fusion protein are designated N and C, respectively. Disordered loops are shown as dashed lines. The stylized black line shows where the cell membrane would be relative to SpsB and the signal peptide in vivo. The inset shows a view of the thioether bond linking the N-­terminus of the Pep3 peptide (blue) to the engineered cysteine residue (Cys78, yellow) on MBP. Residues are encompassed by 2Fo − Fc electron density contoured at 1.0σ, which is orientated to clearly show the continuous electron density between the peptide and Cys78. The peptide position is not constrained by crystal contacts. There is no interaction between the peptide and any adjacent monomers in the crystal lattice, with the nearest adjacent monomer ∼14 Å from the peptide.

IUCrJ
Volume 3| Part 1| January 2016| Pages 10-19
ISSN: 2052-2525
doi:10.1107/S2052252515019971