Insight into structure‐function relationship in phenol‐soluble modulins using an alanine screen of the phenol‐soluble modulin (PSM) α3 peptide

Abstract

Phenol-soluble modulins (PSMs) are a family of peptides with multiple functions in staphylococcal pathogenesis. To gain insight into the structural features affecting PSM functions, we analyzed an alanine substitution library of PSMα3, a strongly cytolytic and proinflammatory PSM of Staphylococcus aureus with a significant contribution to S. aureus virulence. Lysine residues were essential for both receptor-dependent proinflammatory and receptor-independent cytolytic activities. Both phenotypes also required additional structural features, with the C terminus being crucial for receptor activation. Biofilm formation was affected mostly by hydrophobic amino acid positions, suggesting that the capacity to disrupt hydrophobic interactions is responsible for the effect of PSMs on biofilm structure. Antimicrobial activity, absent from natural PSMα3, could be created by the exchange of large hydrophobic side chains, indicating that PSMα3 has evolved to exhibit cytolytic rather than antimicrobial activity. In addition to gaining insight into the structure-function relationship in PSMs, our study identifies nontoxic PSMα3 derivatives for active vaccination strategies and lays the foundation for future efforts aimed to understand the biological role of PSM recognition by innate host defense.

Structural changes of the ligand and of the receptor alters the receptor preference for neutrophil activating peptides starting with a formylmethionyl group

“…The amino acids of the N-terminus in PSMα2 1-16 are identical to those in PSMα2 1-5 and PSMα2 1-10 , respectively, yet the peptides activate different receptors. It is known from earlier studies that the binding pocket in FPR1 has room for no more than five amino acids [15], and when the charge of an FPR1 selective pentapeptide is reduced, such peptides will interact also with FPR2 [31], even if FPR1 is still the preferred receptor [32]. This means that receptor preference is not determined solely by the amino acids that have access to the presumed agonist binding pocket of the receptor, but in part also by amino acids in the peptide that do not have direct access to the binding pocket.…”

“…Our results obtained using PSMα2 variants suggest that the full-length peptide is required for cytolytic activity on apoptotic neutrophils, but since the N-terminus is the part that is essential for neutrophil activation there is no direct link between the cytolytic and the proinflammatory activities. The lack of cytolytic activity of the C-terminal truncated peptides may be related to a reduced capacity to form a α-helix, although it has been suggested that the α-helicity is not correlated with peptide functions, including cytolytic activity [31]. In line with our findings, a recent study using an alanine substitution screen of PSMα3, a closely related S. aureus modulin, demonstrates that the physicochemical property of the amino acids present in C-terminus of PSMα3 (i.e., Lys6, Lys12, Lys17, Asn21 or Asn22) is crucial for the FPR2 binding capacity [31].…”

“…The lack of cytolytic activity of the C-terminal truncated peptides may be related to a reduced capacity to form a α-helix, although it has been suggested that the α-helicity is not correlated with peptide functions, including cytolytic activity [31]. In line with our findings, a recent study using an alanine substitution screen of PSMα3, a closely related S. aureus modulin, demonstrates that the physicochemical property of the amino acids present in C-terminus of PSMα3 (i.e., Lys6, Lys12, Lys17, Asn21 or Asn22) is crucial for the FPR2 binding capacity [31]. It should be noticed, however, that no change in the receptor preference was described, meaning that all the PSMα3 peptide variants tested preferred FPR2 over FPR1.…”

Amyloid Structures as Biofilm Matrix Scaffolds

“…PSMs can be classified according to their length as ␣-PMSs (20 to 25 amino acids), and ␤-PSMs (43 to 45 amino acids). S. aureus expresses four ␣-PSM peptides encoded in the ␣ psm locus, two ␤-PSM peptides encoded in the ␤ psm locus, and the ␦-toxin encoded within RNAIII, the effector molecule of the Agr system (48). These peptides are exported by an ATP-binding cassette (ABC) transporter with two separate membrane components (PmtB and PmtD) and two separate ATPases (PmtA and PmtC) (49).…”

Comparative Analysis of Mineral Elements and Essential Amino Acids Compositions in <i>Juglans sigillata<i> and <i>J. regia<i> Walnuts Kernels

“…In view of lysine, the high content of lysine negatively influenced the uptake of arginine in vivo (Wu and Meininger, 2002). Lysine residues were essential for both receptor-dependent proinflammatory and receptor-independent cytolytic activities (Cheung et al, 2014). In comparison, the results for the composition of essential amino acid in J. sigillata and J. regia from China were consistent with several published reports including those for Spanish almonds (Calixto et al, 1981), New Zealand hazelnuts (Savage and McNeil, 1998), Turkish Tombul hazelnut (Alasalvar et al, 2003), Chilean hazelnut (Villarroel et al, 1987), almond, pecan, pine nut, and pistachio (Ruggeri et al, 1998).…”