Structure of AMH bound to AMHR2 provides insight into a unique signaling pair in the TGF-ß family.

Anti-Müllerian hormone (AMH), or Müllerian-inhibiting substance, is a protein hormone that promotes Müllerian duct regression during male fetal sexual differentiation and regulation of folliculogenesis in women. AMH is a member of the transforming growth factor beta (TGF-ß) family, which has evolved to signal through its own dedicated type II receptor, AMH receptor type II (AMHR2). Structures of other TGF-ß family members have revealed how ligands infer specificity for their cognate receptors; however, it is unknown how AMH binds AMHR2 at the molecular level. Therefore, in this study, we solved the X-ray crystal structure of AMH bound to the extracellular domain of AMHR2 to a resolution of 2.6Å. The structure reveals that while AMH binds AMHR2 in a similar location to Activin and BMP ligand binding to their type II receptors, differences in both AMH and AMHR2 account for a highly specific interaction. Furthermore, using an AMH responsive cell-based luciferase assay, we show that a conformation in finger 1 of AMHR2 and a salt bridge formed by K534 on AMH and D81/E84 of AMHR2 are key to the AMH/AMHR2 interaction. Overall, our study highlights how AMH engages AMHR2 using a modified paradigm of receptor binding facilitated by modifications to the three-finger toxin fold of AMHR2. Furthermore, understanding these elements contributing to the specificity of binding will help in the design of agonists or antagonists or the selection of antibody therapies.

Rivastigmine is a potent inhibitor of acetyl- and butyrylcholinesterase in Alzheimer's plaques and tangles.

Acetylcholinesterase and butyrylcholinesterase activities emerge in association with plaques and tangles in Alzheimer's disease. These pathological cholinesterases, with altered properties, are suggested to participate in formation of plaques. The present experiment assessed the ability of rivastigmine, a clinically utilized agent that inhibits acetylcholinesterase and butyrylcholinesterase activities, to inhibit cholinesterases in plaques and tangles. Cortical sections from cases of Alzheimer's disease were processed using cholinesterase histochemistry in the presence or absence of rivastigmine. Optical densities of stained sections were utilized as a measure of inhibition. The potency of rivastigmine was compared with those of other specific inhibitors. Optimum staining for cholinesterases in neurons and axons was obtained at pH 8.0. Cholinesterases in plaques, tangles and glia were stained best at pH 6.8. Butyrylcholinesterase-positive plaques were more numerous than acetylcholinesterase-positive plaques. Rivastigmine inhibited acetylcholinesterase in all positive structures in a dose-dependent manner (10(-6)-10(-4) M). However, even at the highest concentration, faint activity remained. In contrast, rivastigmine resulted in complete inhibition of butyrylcholinesterase in all structures at 10(-5) M. Rivastigmine was equipotent to the specific acetylcholinesterase inhibitor BW284C51 and more potent than the butyrylcholinesterase inhibitors iso-OMPA and ethopropazine. In conclusion, rivastigmine is a potent inhibitor of acetylcholinesterase and a more potent inhibitor of butyrylcholinesterase in plaques and tangles. Unlike other cholinesterase inhibitors tested, rivastigmine inhibited cholinesterases in normal and pathological structures with the same potency. Thus, at the therapeutic concentrations used, rivastigmine is likely to result in inhibition of pathological cholinesterases, with the potential of interfering with the disease process.