Structure of the mammalian antimicrobial peptide Bac7(1–16) bound within the exit tunnel of a bacterial ribosome

Abstract

Proline-rich antimicrobial peptides (PrAMPs) produced as part of the innate immune response of animals, insects and plants represent a vast, untapped resource for the treatment of multidrug-resistant bacterial infections. PrAMPs such as oncocin or bactenecin-7 (Bac7) interact with the bacterial ribosome to inhibit translation, but their supposed specificity as inhibitors of bacterial rather than mammalian protein synthesis remains unclear, despite being key to developing drugs with low toxicity. Here, we present crystal structures of the Thermus thermophilus 70S ribosome in complex with the first 16 residues of mammalian Bac7, as well as the insect-derived PrAMPs metalnikowin I and pyrrhocoricin. The structures reveal that the mammalian Bac7 interacts with a similar region of the ribosome as insect-derived PrAMPs. Consistently, Bac7 and the oncocin derivative Onc112 compete effectively with antibiotics, such as erythromycin, which target the ribosomal exit tunnel. Moreover, we demonstrate that Bac7 allows initiation complex formation but prevents entry into the elongation phase of translation, and show that it inhibits translation on both mammalian and bacterial ribosomes, explaining why this peptide needs to be stored as an inactive pro-peptide. These findings highlight the need to consider the specificity of PrAMP derivatives for the bacterial ribosome in future drug development efforts.

Structural snapshot of cytoplasmic pre-60S ribosomal particles bound by Nmd3, Lsg1, Tif6 and Reh1

“…First, these factors might test-drive the tunnel as a form of quality control. Second, the presence of their C termini along the entire path of the tunnel might help prevent potential translation inhibitors—for example, the tunnel-targeting antimicrobial peptides produced by insects and mammals 41,42 —from accessing the tunnel.…”

Characterization of the active fragments of Spodoptera litura Lebocin‐1

“…Bovine Bac7 1‐35 binds to bacterial ribosomal proteins (Mardirossian et al, ). Bac7 1‐35 , Pyrrhocoricin, Metalnikowin and two oncocin derivatives block the peptide exit tunnel of 70S ribosome and interfere with the translation initiation (Gagnon et al, ; Seefeldt et al, ). In the future, it will be important to identify the targets of the active fragment to uncover the antimicrobial mechanisms.…”

The Effect of Selective D- or Nα-Methyl Arginine Substitution on the Activity of the Proline-Rich Antimicrobial Peptide, Chex1-Arg20

“…Among these peptides, the class of proline-rich AMPs (PrAMPs) possess a unique multi-modal mechanism of action against pathogens and display potent activity against Gram-negative bacteria (Otvos et al, 2005; Czihal et al, 2012; Guida et al, 2015). These actions include membrane rupture (Li et al, 2014), inhibition of the bacterial shock heat protein DnaK (Kragol et al, 2001; Scocchi et al, 2009), blockade of bacterial ribosomal protein expression (Krizsan et al, 2014; Roy et al, 2015; Seefeldt et al, 2015, 2016; Goldbach et al, 2016), and immunostimulatory activity (Ostorhazi et al, 2011). Recently, a PrAMP and other AMPs were impregnated into nanofibers or hydrogels for the potential treatment of skin injuries in general and battlefield burns (Mateescu et al, 2015; Sebe et al, 2016).…”