Daniel A. Holdbrook, Shalini Singh, Yeu Khai Choong, Jitka Petrlova, Martin Malmsten, Peter J. Bond, Navin Kumar Verma, Artur Schmidtchen, Rathi Saravanan, Influence of pH on the activity of thrombin-derived antimicrobial peptides, Biochimica et Biophysica Acta (BBA) - Biomembranes, Volume 1860, Issue 11, 2018, Pages 2374-2384, ISSN 0005-2736, https://doi.org/10.1016/j.bbamem.2018.06.002.
Abstract:
The wound environment is characterized by physiological pH changes. Proteolysis of thrombin by wound-derived proteases, such as neutrophil elastase, generates antimicrobial thrombin-derived C-terminal peptides (TCPs), such as HVF18 (HVFRLKKWIQKVIDQFGE). Presence of such TCPs in human wound fluids in vivo, as well as the occurrence of an evolutionarily conserved His residue in the primary amino acid sequence of TCPs, prompted us to investigate the pH-dependent antibacterial action of HVF18, as well as of the prototypic GKY25 (GKYGFYTHVFRLKKWIQKVIDQFGE). We show that protonation of this His residue at pH 5.5 increases the antibacterial activity of both TCPs against Gram-negative Escherichia coli by membrane disruption. Physiological salt level (150 mM NaCl) augments antibacterial activity of GKY25 but diminishes for the shorter HVF18. Replacing His with Leu or Ser in GKY25 abolishes the His protonation-dependent increase in antibacterial activity at pH 5.5, whereas substitution with Lys maintains activity at neutral (pH 7.4) and acidic pH. Interestingly, both TCPs display decreased binding affinities to human CD14 with decreasing pH, suggesting a likely switch in mode-of-action, from anti-inflammatory at neutral pH to antibacterial at acidic pH. Together, the results demonstrate that apart from structural prerequisites such as peptide length, charge, and hydrophobicity, the evolutionarily conserved His residue of TCPs influences their antibacterial effects and reveals a previously unknown aspect of TCPs biological action.
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Funding Info:
This research was supported by the Lee Kong Chian School of Medicine, Nanyang Technological University Singapore Postdoctoral Fellowship 2014 (L0491020) to RS. The authors acknowledge the Lee Kong Chian School of Medicine, Nanyang Technological University Singapore Start-Up Grants (AS and NKV), Singapore Ministry of Education under its Singapore Ministry of Education Academic Research Fund Tier 1 (2015-T1-001-082) (AS/NKV), the Knut and Alice WallenbergFoundation,theSwedishFoundationforStrategicResearch, the Swedish Research Council projects (projects 2012-1883 and 201702341) (AS), project 2016-05157 (MM), and the LEO Foundation Center for Cutaneous Drug Delivery (2016-11-01) (MM).
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The full paper is available for download at the publisher's URL here: https://doi.org/10.1016/j.bbamem.2018.06.002