Characterizing the Structure and Oligomerization of Major Royal Jelly Protein 1 (MRJP1) by Mass Spectrometry and Complementary Biophysical Tools

Royal jelly (RJ) triggers the development of female honeybee MRJP1 larvae into queens. This effect has been attributed to the presence of major royal jelly protein 1 (MRJP1) in RJ. MRJP1 isolated from royal jelly is tightly associated with apisimin, a 54-residue alpha-helical peptide that promotes the noncovalent assembly of MRJP1 into multimers. No high-resolution structural data ate available for these complexes, and their binding stoichiometry, remains uncertain. We examined MRJP(1)/apisimin using a range of biophysical techniques. We also investigated the behavior of deglycosylated samples, as well as samples with reduced apisimin content, Our mass spectrometry (MS) data demonstrate that the native complexes predominantly exist in a (MRJP1(4) apisimin(4)) stoichiometry. Hydrogen/deuterium exchange MS reveals that MRJP1 within these complexes is extensively disordered in the range of residues 20-265. Marginally stable secondary structure (likely antiparallel beta-sheet) exists around residues 266-432. These weakly structured regions interchange with conformers that are extensively unfolded, giving rise to bimodal (EX1) isotope distributions; We propose that the native complexes have a "dimer of dimers" quaternary structure in which MRJP1 chains are bridged by apisimin. Specifically, our data suggest that apisimin acts as a linker that forms hydrophobic contacts involving the MRJP1 segment (316)VLFFGLV(322). Deglycosylation produces large soluble aggregates, highlighting the role of glycans as aggregation inhibitors. Samples with reduced apisimin content form dimeric complexes with a (MRJP1(2) apisimin(1)) stoichiometry. The information uncovered in this work will help pave the way toward a better understanding of the unique physiological role played by MRJP1 during queen differentiation.