Team:XJTLU-CHINA/PeptideProduction

Peptide Production

Anti-Microbial Peptide

Anti-microbial peptide (AMP) is a part of the innate immune system of most multi-cellular organisms to counter microbial infections (Margitta and Torsten, 1999). The cationic and amphipathic α-helix structure is the most wildly conformation in those peptides but some hydrophobic α-helical peptides which possess antimicrobial activity. This year we choose three different cationic antimicrobial peptides which encompass α-helical conformation in our project.

Figure 1 shows the molecular mechanism of cationic AMPs α-helical structure. Most of cationic AMPs associate with lipid group of bacteria membrane. The α-helical structure disrupt the packing of lipid molecules such that the membrane becomes leaky (Rocca et al., 1999).

1: The interaction mechanism of cationic α-helical structure of Anti-microbial peptides. The α-helical structure insert into the bacteria Lipid bilayer in aqueous solution. Following insertion of the peptide, the bilayer membrane permeability may be varied.

LL-37

LL-37 is the only cathelicidin-derived antimicrobial peptide found in humans (Dürr, Sudheendra and Ramamoorthy, 2006). Mature LL-37 has 37 amino acid residues starting with two leucines (NH2-LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES-COOH). The peptide is cleaved from a larger protein, hCAP-18 by extracellular proteolysis of proteinase 3 from the C-terminal end of hCAP18 (Patricia, 2010; Ramos, Domingues, and Gama, 2011). The peptide composed of two mainly parts: from residue Leu2 to Leu31 is α-helical structure (Fig 2b) and 6 residues form loop structure (Fig 2a).

Ramos, Domingues, and Gama (2011) also reported that LL-37 has additional roles such as regulating the inflammatory response to wound or infection sites, binding and neutralizing LPS, and wound closure apart from anti-microbial property (Figure 2c).

2a: LL-37 structure and residues（PDB 2K6O）

Figure 2b: LL-37 secondary structure prediction (predicted by http://www.compbio.dundee.ac.uk/jpred/index.html ).

2c: Biological functions of LL-37 (Ramos, Domingues, and Gama, 2011)

GF-17

GF-17 is a high efficiency anti-microbial peptide which modified from LL-37 residue Phe-17 to Val-32 (Fig 3a).

Figure 3a: GF-17 is modified from LL-37. Amino acid residue Gly-16 is modified.

Figure3b: Cartoon view of GF-17 structure (PDB: 2L5M)

Table shows the Minimal Inhibitory concentration (MIC) of Anti-microbial peptides GF-17, GF-18 and their variants. GF-17 was capable of eliminating both Gram-positive and Gram-negative bacteria, such as S. aureus USA300 and E. coli K-12 in vitro (Wang et al., 2011). Additionally, to compare with LL-37, GF-17 has highly efficiency on anti-Staphylococcus aureus biofilm and killing efficiency (Fig 3c, table) ( Mishra et al., 2016; Wang et al., 2011 ).

Table: Antimicrobial activity (MIC in μM) of GF-17, GE-18 and their variants (Wang et al., 2011)

Figure 3c: anti-Staphylococcus aureus Biofilm assay. Two different Staphylococcus aureus strain: USA200 and USA300. The result shows the GF-17 has more efficiency to anti-Staphylococcus aureus Biofilm.( Mishra et al., 2016)