Antibacterial activity of major royal jelly proteins of the honeybee (Apis mellifera) royal jelly

Major royal jelly proteins (MRJPs) are the protein components in royal jelly (RJ). MRJPs 1-7 are detected in the honeybee Apis mellifera RJ. Although A. mellifera MRJP (AmMRJP) 2 exhibited antibacterial activity, the other MRJPs with antimicrobial activities in A. mellifera RJ remains largely unknown. Here, we compared the antibacterial activity of recombinant AmMRJPs 1-7 expressed in baculovirus-infected insect cells. Antibacterial assays of recombinant AmMRJPs 1-7 against the gram-negative bacterium Escherichia coli revealed that AmMRJPs 2-5 and 7 exhibited antibacterial activity, whereas AmMRJPs 1 and 6 displayed almost no antibacterial activity. Consistent with the antibacterial activity of AmMRJPs, AmMRJPs 2-5 and 7 are bound to bacterial cell walls. These results indicated that AmMRJPs 2-5 and 7 contribute directly to the antibacterial property of RJ, suggesting that MRJPs play a role in the antimicrobial property of RJ.