Casecidin 15

Introduction: More than half of the world's population is infected with Helicobacter pylori, which may cause gastritis, peptic ulcer and even gastric cancer. The World Health Organization (WHO) has announced that H. pylori infection is a class I carcinogen and hence eradication of it is highly important. Bovine milk contains caseins, which can be digested by various enzymes in the human stomach to produce antibacterial peptides. Material and methods: This study used in vitro methods to extract anti-H. pylori peptides from caseins by the gastric protease pepsin under environments with similar pH values to those found in the human stomach. The molecular weights and sequences of the peptides were identified by MALDI-TOF mass spectrometry and MS/MS Ion Search, respectively. Antibacterial activity tests were performed to calculate the minimum inhibitory concentration (MIC90) of the extracts. Results: The findings of this study revealed that the major products of bovine milk casein digestion by pepsin are casecidin 17 and β-casein 207-224. The extracts produced promising anti-H. pylori effects with the lowest MIC90 found at pH values of 1.5 and 2.0. Conclusions: This study identified the anti-H. pylori effects of casecidin 17 and β-casein 207-224, which may help in developing therapeutic agents to modulate the effect of antibiotics on H. pylori infections.

Aims: To isolate and characterize peptides from bovine colostrum with antimicrobial activity. Methods and results: Three peptides were purified from fresh colostrum by a range of chromatographic methods using antimicrobial activity against Escherichia coli DH5alpha to screen for the most active fractions. Two peptides, with antimicrobial activity, casecidin 17 and casecidin 15, were identical to sequences in the C-terminal of bovine beta-casein (YQEPVLGPVRGPFPIIV and YQEPVLGPVRGPFPI) and had corresponding molecular masses of 1881.00 and 1669.06 Da, respectively. The third peptide was the known peptide isracidin which has a mass of 2763.80 Da and sequence of RPKHPIKHQGLPQEVLNENLLRF. Casecidin 17 and casecidin 15 had identical minimal inhibition concentrations (MICs) against E. coli DPC6053 of 0.4 mg ml(-1). Structural modelling suggested amphiphilic structures having identical inhibitory and structural properties. The MIC value of isracidin against E. coli DPC6053 was 0.2 mg ml(-1). Conclusions: This study shows the presence of three antimicrobial peptides in colostrum which may contribute to a bioprotective role to limit pathogen contamination. Furthermore, the discovery of casecidin 17 and 15 may provide the basis for novel antimicrobial peptide design. Significance and impact of the study: This is the first study to characterize peptides with antimicrobial activity present in fresh bovine colostrum.