PH-dependent stability of honey bee (Apis mellifera) major royal jelly proteins

Carmen I Mureşan,Anja Buttstedt

doi:10.1038/s41598-019-45460-0

Abstract

Honey bee larval food jelly is a secretion of the hypopharyngeal and mandibular glands of young worker bees that take care of the growing brood in the hive. Food jelly is fed to all larvae (workers, drones and queens) and as royal jelly to the queen bee for her entire life. Up to 18% of the food jelly account for proteins the majority of which belongs to the major royal jelly protein (MRJP) family. These proteins are produced in the hypopharyngeal glands at a pH value of 7.0. Before being fed to the larvae, they are mixed with the fatty acids secreted by the mandibular glands of the worker bees resulting at a pH of 4.0 in the food jelly. Thus, MRJPs are exposed to a broad pH range from their site of synthesis to the actual secreted larval food. We therefore determined the pH-dependent stability of MRJP1, MRJP2 and MRJP3 purified from royal jelly using differential scanning fluorimetry. All MRJPs were much more stable at acidic pH values compared to neutral ones with all proteins showing highest stability at pH 4.0 or 4.5, the native pH of royal jelly.

Highlights

Honey bees (Apis sp.) feed their growing larvae with a special food jelly, a secretion produced by the hypopharyngeal and mandibular glands of nurse worker bees that take care of the brood in the hive[1,2]
(3) Only very recently it has been revealed that the complex of oligoMRJP1 and apisimin binds in addition eight molecules of 24-methylenecholesterol[41] which explains most likely the high hydrophobicity
OligoMRJP1/apisimin appears to have an increased stability compared to monoMRJP1, irrespective of the fact that some hydrophobic residues are already exposed at low temperatures

Summary

Introduction

Honey bees (Apis sp.) feed their growing larvae with a special food jelly, a secretion produced by the hypopharyngeal and mandibular glands of nurse worker bees that take care of the brood in the hive[1,2]. Extreme temperatures reach from 6 °C (bee in the periphery of the winter cluster)[33] to 46 °C (bees with activated flight muscles attacking a wasp)[34] These extreme temperatures might be irrelevant for MRJPs in the food jelly, as the brood is raised at constant temperatures of 34 °C32, but might become important for MRJPs being present in the bee venom, the brain and the hemolymph. Most proteins do have their stability optimum at a pH of 7.0 or 7.5 and only very few proteins are stable at a pH below 4.535 Exactly at these acidic pH values MRJPs need to be stable as they reach their highest incidence in royal jelly at pH 4.0.

Methods

Results

Conclusion