Moonlighting Peptides with Emerging Function

<div><p>Hunter-killer peptides combine two activities in a single polypeptide that work in an independent fashion like many other multi-functional, multi-domain proteins. We hypothesize that emergent functions may result from the combination of two or more activities in a single protein domain and that could be a mechanism selected in nature to form moonlighting proteins. We designed moonlighting peptides using the two mechanisms proposed to be involved in the evolution of such molecules (<em>i.e</em>., to mutate non-functional residues and the use of natively unfolded peptides). We observed that our moonlighting peptides exhibited two activities that together rendered a new function that induces cell death in yeast. Thus, we propose that moonlighting in proteins promotes emergent properties providing a further level of complexity in living organisms so far unappreciated.</p> </div

Antibacterial and mitochondrial swelling activities of Iztli peptides.

<p>The activity for Iztli peptide IP1 (20 µM) (▪ in <b>A</b>, black bars in <b>B</b>) against the bacteria <i>E. coli</i> (DH10B) was tested in two ways: following the optical cell density of the culture at 600 nm (<b>A</b>) and counting the colony forming units (CFU) (<b>B</b>). Three controls are included: LB with no peptide (<b>▪</b> in <b>A</b>, white bars in <b>B</b>)<b>,</b> α-pheromone (25 µM; ▪ in <b>A</b>, gray bars in <b>B</b>) and the six residues at the N-terminus of IP1 (fIP1) (119 µM; ⋄ in <b>A</b>)<b>.</b> The results of 4 experiments are presented for plots in <b>A</b> and <b>B</b>. The bars represent standard deviations. Mitochondrial swelling was followed at 540 nm (<b>C</b>) in the presence of Iztli peptide IP1 (▪ 117 µM); three controls were used: distilled water (<b>▪)</b>, α-pheromone (▪ 160 µM) and fIP1 (⋄ 100 µM), Polyethylene glycol 3.4 kDa was added at 180 seconds. Only the IP1 data is shown here; the 3 other IP peptides display similar activity than IP1.</p

Antifungal activity of Iztli peptides.

<p>The activity of the Iztli peptide IP1 (10 µM) (▪ in <b>A</b>, black bars in <b>B</b>) against the MatA cells from <i>Saccharomyces cerevisiae</i> (BY4741) is presented in two formats: Optical cell density (<b>A</b>) and CFU (<b>B</b>). Cells were grown in YPD. We used three controls: No peptide (<b>▪</b> in <b>A</b>, white bars in <b>B</b>), α-pheromone (10 µM) (▪ in <b>A</b>, gray bars in <b>B</b>) and the six residues at the N-terminus (fIP1) (60 µM) (⋄ in <b>A</b>). The results of 4 experiments are presented for plots in <b>A</b> and <b>B</b>. The error bars represent standard deviations. The strain BY4741 Δ<i>STE2</i> lacking the receptor for the α-pheromone was tested against the Iztli peptides (<b>C</b>): IP1 ▪ 10 µM, IP2 ▪ 10 µM for antifungal activity. For these experiments we used no peptide <b>▪</b> and α-pheromone ▪ (10 µM) as controls.</p