Citrullinated human and murine MOG35-55 display distinct biophysical and biochemical behavior

The peptide spanning residues 35 to 55 of the protein myelin oligodendrocyte glycoprotein (MOG) has been studied extensively in its role as a key autoantigen in the neuroinflammatory autoimmune disease multiple sclerosis. Rodents and nonhuman primate species immunized with this peptide develop a neuroinflammatory condition called experimental autoimmune encephalomyelitis, often used as a model for multiple sclerosis. Over the last decade, the role of citrullination of this antigen in the disease onset and progression has come under increased scrutiny. We recently reported on the ability of these citrullinated MOG35-55 peptides to aggregate in an amyloid-like fashion, suggesting a new potential pathogenic mechanism underlying this disease. The immunodominant region of MOG is highly conserved between species, with the only difference between the murine and human protein, a polymorphism on position 42, which is serine in mice and proline for humans. Here, we show that the biophysical and biochemical behavior we previously observed for citrullinated murine MOG35-55 is fundamentally different for human and mouse MOG35-55. The citrullinated human peptides do not show amyloid-like behavior under the conditions where the murine peptides do. Moreover, we tested the ability of these peptides to stimulate lymphocytes derived from MOG immunized marmoset monkeys. While the citrullinated murine peptides did not produce a proliferative response, one of the citrullinated human peptides did. We postulate that this unexpected difference is caused by disparate antigen processing. Taken together, our results suggest that further study on the role of citrullination in MOG-induced experimental autoimmune encephalomyelitis is necessary.

Design and Synthesis of Quenched Activity-based Probes for Diacylglycerol Lipase and α,β-Hydrolase Domain Containing Protein 6

Diacylglycerol lipases (DAGL) are responsible for the biosynthesis of the endocannabinoid 2-arachidonoylglycerol. The fluorescent activity-based probes DH379 and HT-01 have been previously shown to label DAGLs and to cross-react with the serine hydrolase ABHD6. Here, we report the synthesis and characterization of two new quenched activity-based probes 1 and 2, the design of which was based on the structures of DH379 and HT-01, respectively. Probe 1 contains a BODIPY-FL and a 2,4-dinitroaniline moiety as a fluorophore-quencher pair, whereas probe 2 employs a Cy5-fluorophore and a cAB40-quencher. The fluorescence of both probes was quenched with relative quantum yields of 0.34 and 0.0081, respectively. The probes showed target inhibition as characterized in activity-based protein profiling assays using human cell- and mouse brain lysates, but were unfortunately not active in living cells, presumably due to limited cell permeability.