The Dolphin Proline-Rich Antimicrobial Peptide Tur1A Inhibits Protein Synthesis by Targeting the Bacterial Ribosome

Abstract

Proline-rich antimicrobial peptides (PrAMPs) internalize into susceptible bacteria using specific transporters and interfere with protein synthesis and folding. To date, mammalian PrAMPs have so far been identified only in artiodactyls. Since cetaceans are co-phyletic with artiodactyls, we mined the genome of the bottlenose dolphin Tursiops truncatus, leading to the identification of two PrAMPs, Tur1A and Tur1B. Tur1A, which is orthologous to the bovine PrAMP Bac7, is internalized into Escherichia coli, without damaging the membranes, using the inner membrane transporters SbmA and YjiL/MdM. Furthermore, like Bac7, Tur1A also inhibits bacterial protein synthesis by binding to the ribosome and blocking the transition from the initiation to the elongation phase. By contrast, Tur1B is a poor inhibitor of protein synthesis and may utilize another mechanism of action. An X-ray structure of Tur1A bound within the ribosomal exit tunnel provides a basis to develop these peptides as novel antimicrobial agents.

Search for Shorter Portions of the Proline‐Rich Antimicrobial Peptide Fragment Bac5(1–25) That Retain Antimicrobial Activity by Blocking Protein Synthesis

“…PrAMPs( such as Bac5) remaine xtended, with significant polyproline II helix content, [4a, 16] also due to the characteristic prolinep attern with repeated Pro-Pro pairs. Because all the peptides analyzed in this study displayed very similarC Ds pectra despite different antimicrobial activity,t his structurala spectd oes not appear to play an important role in the antibacterial activity of Bac5f ragments.B ac5 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), the only peptide that shows as lightly different CD spectrum, is also the only inactive fragment, but this correlation may just be coincidental. However,t he structuration (if any) of Bac5(1-25) fragments did not result in permeabilizing the bacterial membranes, as they are all completely nonlytic molecules, like the parental Bac5(1-25).…”

“…No dramatic changes in the CD spectra were observed as ac onsequence of the shortening of Bac5(1-25), or changing the solvent polarity (i.e.,i ntroducing SDS micelles or trifluoroethenol). Slight changes were detected only for Bac5 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) with respect to the other peptides, because this shortest fragment was the only one displaying am arked positive peak at 195 nm under all the conditions tested.…”

“…[6] Moreover, PrAMPsa lso have significant antimicrobiala ctivity againstp athogens that lack SbmA, such as Pseudomonas aeruginosa,e xploiting as econdary lytic mechanism of action. [10] Moreover,i th as been demonstrated that Bac5(1-25) is the most active Bac5 fragment against E. coli,w hile the lack of antimicrobial activity of the shorter Bac5 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) [9][10] is due to poor inhibitory activity toward protein synthesis. Native PrAMPs have been modified to expand their therapeutic index andr ange of activity,toi ncrease their stability and permanencei nt he body,o rt oo btain smaller and therefore less expensive molecules whilestill retaining the antimicrobial potential of the original peptide.…”

BioSAXS measurements reveal that two antimicrobial peptides induce similar molecular changes in Gram-negative and Gram-positive bacteria

“…There is a large variety of structures and sequences of AMPs and in recent years it has become clear that there are also a variety of targets (Le et al, 2017). Today, there is a huge body of literature regarding AMPs, however there is only few articles published on target validation, pharmacological and safety studies (Czaplewski et al, 2016;Greber and Dawgul, 2017;Mardirossian et al, 2018a;Schmitt et al, 2010). This contributes to the fact that only a few AMPs are enrolled in clinical studies.…”

“…In the last two decades of AMP research it has become clear that these molecules have multiple biological activities, including antimicrobial, antiparasitic, anticancer and immunomodulatory properties (Mahlapuu et al, 2016). In the same time period multiple bacterial targets of AMPs were discovered (Brogden, 2005), for example binding to RNA, DNA or histones (Cho et al, 2009;Hale and Hancock, 2007;Kobayashi et al, 2000;Xie et al, 2011) blocking DNA-dependent enzymes (Hilpert et al, 2010;Marchand et al, 2006), blocking the synthesis of important outer membrane proteins (Carlsson et al, 1991), binding to the chaperon DnaK and the ribosome (Knappe et al, 2016;Krizsan et al, 2015;Mardirossian et al, 2018b) and lipid 2 (de Leeuw et al, 2010;Schmitt et al, 2010). In addition, the effect of such peptides on blood components was studied (Yu et al, 2015).…”