Royal jelly (RJ) is a well-known functional and medicinal food for human health promotion. Major royal jelly proteins (MRJPs), which are the major protein components in RJ, exhibit antimicrobial activities. However, the identities of the MRJPs of RJ responsible for its antioxidant effects have remained unclear. Here, we report that honeybee (Apis cerana) MRJP 2 (AcMRJP2) acts as an antimicrobial and antioxidant agent in RJ. Using recombinant AcMRJP2, which was produced in baculovirus-infected insect cells, we established the antimicrobial and antioxidant roles of MRJP 2. AcMRJP2 bound to the surfaces of bacteria, fungi, and yeast, which then induced structural damage in the microbial cell walls and led to a broad spectrum of antimicrobial activities. AcMRJP2 protected mammalian and insect cells via the direct shielding of the cell against oxidative stress, which led to reduced levels of caspase-3 activity and oxidative stress-induced cell apoptosis, followed by increased cell viability. Moreover, AcMRJP2 exhibited DNA protection activity against reactive oxygen species (ROS). Our data indicate that AcMRJP2 could play a crucial role as an antimicrobial agent and antioxidant in RJ, suggesting that MRJP 2 is a component responsible for the antimicrobial and antioxidant activities of RJ.

Major royal jelly proteins (MRJPs), important protein components of bee royal jelly (RJ) and exclusive nourishments for queen, exhibit various biological and pharmacological activities. RJ is one of the most studied bee products, but the crucial roles for MRJP2 as an antimicrobial and antioxidant agents remain largely unknown. Here we demonstrated the antimicrobial and antioxidant functions of the Asiatic honeybee (Apis cerna) MRJP2 (AcMRJP2). Recombinant AcMRJP2 of approximately 53 kDa was expressed in baculovirus-infected insect cells, and it exhibited antimicrobial activity against bacteria, fungi, and yeast via binding to microbial surfaces and inducing structural damage in microbial cell walls. AcMRJP2 protected mammalian and insect cells against oxidative damage through shielding of cell membranes. Interestingly, AcMRJP2 exhibited DNA protection activity and DPPH radical-scavenging activity. Altogether, our data demonstrated that AcMRJP2 functions as antimicrobial and antioxidant agents.

Major royal jelly proteins (MRJPs) are important protein components of bee royal jelly (RJ) and exhibit various biologicaland pharmacological activities. The antimicrobial activities of royalisins and the jelleines contained within MRJP 1 andMRJP 2 in RJ have been elucidated. However, the antimicrobial effects of other bee RJ MRJPs remain largely unknown.In this study, we demonstrated that the Asiatic honeybee (Apis cerana) MRJP 4 (AcMRJP4) exhibits antimicrobial activitiesagainst bacteria, fungi, and yeast. Recombinant AcMRJP4 was expressed as a 63-kDa protein in baculovirus-infected insectcells. However, some of the recombinant AcMRJP4 proteins were cleaved into two fragments (i.e., 48-kDa (AcMRJP4-48)and 15-kDa (AcMRJP4-15) proteins) by the proteolytic cleavage of the C-terminus of the recombinant AcMRJP4. Interestingly,AcMRJP4, AcMRJP4-48, and AcMRJP4-15 exhibited antimicrobial activities, with AcMRJP4-15 exhibiting the highestantimicrobial activity, followed by AcMRJP4. AcMRJP4-15, which is a hydrophilic peptide with 88 amino acid residuesthat contains a high content of Asn and positively charged amino acids, induced structural damage in the cell walls ofthe assayed bacteria, fungi, and yeast. Altogether, our data demonstrated that AcMRJP4 functions as an antimicrobial agent.

The native human saliva obtained through the centrifugation of whole saliva showed characteristic salivary protein complex (SPC) peaks in gel filtration high performance liquid chromatography (HPLC) using Superose 12 column1,2). In the previous study the SPC peaks in chromatography were explored to know their composition and functions by different detection methods, but still the nature of SPCs was not clearly elucidated so far. In this study the SPC peaks were examined by direct antibody interaction in order to target different antimicrobial and protective proteins distributed in the SPCs via gel filtration HPLC. As the SPC peak shape and migration speed can be changed by antibody binding to specific proteins of SPC, it was found that mucin1 is evenly distribution in all SPCs, while PRPs are more abundant in the late dominant SPC than the early dominant SPC and also in the intermediated SPCs. Most of antimicrobial proteins including lysozyme, LL-37, lactoferrin, β-defensin-1, -2, -3, IgA, mucocidin, and α1-antitrypsin were more abundant in the late dominant SPC than the early dominant SPC, while histatin showed relatively even distribution in all SPCs. Therefore, it was presumed that the late dominant SPC containing abundant antimicrobial and protective proteins could be applied as a biomarker to measure the defensive potential of whole saliva in oral diseases.

In the previous molecular cloning study from human salivary gland cDNA l ibrary a novel clone (C77-091) was known as a candidate gene for antimicrobial protein by GenBank database search and RNA in situ hybridization. This study is aimed to identify the molecular characteristics of C77-091 protein, which showed an antimicrobial activity on E.coli, thereby named as salivary antimicrobial protein (SAMP). SAMP consisted of a typical hydrophobic amino acid rich domain in the N-terminus, a cluster of basic amino acids, carbohydrate attachment site, a possible transglutaminase catalyzed cross-linking site, and multiple consensus sequences of phosphorylation site in the C-terminus. Western blot analysis of human organs and tissue with the monospecific antibody to the synthetic SAMP peptide showed strong interacting protein from the extracts from submandibular gland and parotid saliva but absent in the mixed saliva, and the immunohistochemical staining detected a strong positive regions in the secretory granules in the luminal cytoplasm of interlobular ductal cells of salivary gland. The SAMP was also distributed in the human sebaceous gland and prostate. These data suggest that C77-091 named SAMP gene is a novel antimicrobial protein in human salivary gland, which may play a role for the innate immunity by protecting and stabilizing the mucosal epithelium to maintain homeostasis of oral mucosa.