Protein and lipid interactions of mammalian antibacterial peptides

<p>Gene-encoded antibacterial peptides are multifunctional effector molecules and play an important role in host innate immunity. Upon stimulation, the mature active peptides are released from inactive precursors. Cathelicidins constitute a family of antibacterial peptides, which share a conserved N-terminal cathelin-like region followed by a variable C-terminal antibacterial domain.</p><p>In addition to its antibacterial activity, LL-37, the only cathelicidin found in human, is cytotoxic at concentrations higher than the bactericidal concentration. An LL-37 binding protein was purified from human plasma and identified as apolipoprotein A-I (apoA-I). A KD value of 0.6-2.4 µM for the interaction between LL-37 and apoA-1 was determined, and this translates to approximately 90% scavenging of LL-37 at physiological apoA-I plasma concentrations. In an inhibition zone assay, apoA-I gave 50 % of the inhibition attained by plasma, and addition of anti-apoA- I IgG to plasma partly restored the LL-37 antibacterial activity. This suggested that apoA-I can modulate the concentration of free LL- 37, thereby preventing cytotoxic effects.</p><p>Porcine cathelicidin prophenin (PF) and an 18-residue fragment thereof (PF-18) were found in organic extracts of lung tissues and also in a porcine surfactant preparation. Structure analysis by mass spectrometry revealed a mixture of variant forms of prophenin, including 79-residue PF-1, 80-residue PF-2 with N-terminal Gln and 80residue PF-2 with N-terminal pyroglutamic acid.</p><p>The antibacterial activity of LL-37 and PF were affected by different factors. PF was more active at lower salt concentrations. In the presence of surfactant preparations, the activity of LL-37 and PF-18 against group B stretptoccoci (GBS) were inhibited in a dose-dependent manner, which was likely to be caused by peptide binding to surfactantlipids.</p><p>From human granulocytes obtained after treatment with granulocyte-colony stimulating factor (G-CSF) and cortisol, several histone fragments were isolated which exhibited activity against B. megateriumin Bm11 Among these, two Cterminal histone H1A fragments were characterised, corresponding to Lys152-Lys222 and Lys167-Lys222, and both were modified by conjugation of the C-terminal carboxyl group of the tripeptide Arg-Gly-Gly to the side chain amino group of Lys222 via an isopeptide bond. The C-terminal tripeptide Arg- Gly-Gly corresponds uniquely to the three C-terminal residues of ubiquitin. This is the first evidence for ubiquitination of histone H1A.</p><p>The interpretation of the tandem mass spectra leading to characterisation of the histone H1A modification was aided by a knowledge of the gas-phase ion chemistry leading to the proline effect. From studies of proline rich PF it was suggested that cleavage of Pro-Pro and Pro- Xxx amide bonds proceeds with the formation of (protonated) substituted diketopiperazines or cyclic peptides as the N-terminal fragments and (protonated) peptides as the C-terminal fragments.</p><h3>List of scientific papers</h3><p>I. Wang Y, Agerberth B, Lothgren A, Almstedt A, Johansson J (1998). "Apolipoprotein A-I binds and inhibits the human antibacterial/cytotoxic peptide LL-37." J Biol Chem 273(50): 33115-33118 <br><a href="https://pubmed.ncbi.nlm.nih.gov/9837875">https://pubmed.ncbi.nlm.nih.gov/9837875</a><br><br></p><p>II. Wang Y, Griffiths WJ, Curstedt T, Johansson J (1999). "Porcine pulmonary surfactant preparations contain the antibacterial peptide prophenin and a C-terminal 18-residue fragment thereof." FEBS Lett 460(2): 257-262 <br><a href="https://pubmed.ncbi.nlm.nih.gov/10544246">https://pubmed.ncbi.nlm.nih.gov/10544246</a><br><br></p><p>III. Wang Y, Johansson J, Griffiths WJ (2000). "Characterisation of variant forms of prophenin: mechanistic aspects of the fragmentation of proline-rich peptides." Rapid Commun Mass Spectrom 14(23): 2182-2202 <br><a href="https://pubmed.ncbi.nlm.nih.gov/11114029">https://pubmed.ncbi.nlm.nih.gov/11114029</a><br><br></p><p>IV. Wang Y, Johansson J, Griffiths WJ, (2000). "Antibacterial activitiy of the cathelicidins prophenin (62-79)and LL-37 in the presence of a lung surfactant preparation." (Manuscript)</p><p>V. Wang Y, Griffiths WJ, Jörnvall H, Agerberth B, Johansson J (2001). "Antibacterial peptides in stimulated human granulocytes: Characterisation of ubiquitinated histone H1A." (Submitted)</p>