Synthesis And Properties Of The Minic Bovini Lactoferrin-based Antibacterial Peptides

Because of the bacteria resistance to antibiotics, antibacterial peptides will gradually take place of the antibiotics. Bovini Lactoferricin-Based Antibacterial Peptides (BLFB) have broad-spectrum antibacterial activity without toxicity to eukaryotic cells. It is important significance and practical value to understand the factors and mechanism.The main contents of this paper includes the following points:1. Based on the orginal peptides (FKCRRWQWRM), seventeen kinds of new peptides rich in tryptophan were synthesized by Fmoc Solid-phase Strategy. Hexapeptide:KKWAWK, KKWWWK, KWQWKK, RWQWRK, KKWQWK; Octapeptide:KKWQWKHL, WKWWWKWL, KWQWKKAK, KKWQWKWL, WKWQWKWL, KKWWWKWL, KKWWWKHL, KKWWWWWL, KWWWWKWL; Decapeptide:LHKKWQWKHL, KKWQWKHLHL; Dodecapeptide:LHLHKKWQWKHL.The above seventeen antibacterial peptides have not been reported.2. The peptides were analysed and purified by Reverse Phase HPLC, the purity of the obtained products was bigger than90%. The seventeen antibacterial peptides were characterized by ESI-MS.3. The MIC values of the eighteen peptides against Escherichia coli and staphylococcus aureus were determined by Standard Trace Dilution Method.(1) The MIC values of KKWWWKWL and KKWWWWWL to Escherichia coli and Staphylococcus aureus were both smaller than the MIC value of the FKCRRWQWRM. This indicates that three or more consecutive tryptophans in the peptides were helpful to increase the antibacterial activity.(2) The MIC values of the hexapeptides were bigger than500μg/mL. The antibacterial activity was weak when the peptide chain was short.(3) The MIC values of LHKKWQWKHL and LHLHKKWQWKHL against Escherichia coli were100μg/mL and27μg/mL, this result shows that the increase of the number of amino acid that tends to form a-helical structure at N termine was helpful to increase the antibacterial activity, while it was useless at C termine.(4) The grand average of hydropathicity was in the range from1.0to1.5, the peptides have obvious antibacterial actvity.4. The interaction of the seven peptides with CT-DNA was determined by ultraviolet absorption spectrometry and fluorescence spectroscopy.(1) LHLHKKWQWKHL, LHKKWQWKHL and KKWQWKHLHL can strongly combine with DNA. The DNA-binding modes might be intercalation or groove interaction as well as electrostatic mode. DNA can obviously quench the fluorescence of the three peptides, the quenching costant were3.76×105L·mol-1,8.8×104L-mol-1,8.3×104L-mol-1, respectively. This could be due to the long peptides chain tending to form a-helical structure and the aromatic groups from tryptophan and histidine easy to bind DNA.(2) The DNA-binding of the octapeptides was followed by KKWQWKHL> WKWQWKWL>KKWQWKWL> KKWWWKWL. KKWWWKWL could interact with DNA by electrostatic mode, while the others were combined with DNA by insert or groove mode.