Territrem B

Territrem C, a new tremorgenic mycotoxin (C28H32O9; molecular weight, 512.20) was isolated from the chloroform extract of rice cultures of Aspergillus terreus 23-1, which also produces territrems A and B. Isolation, acute toxicity, and some physicochemical properties of territrem C are discussed in this paper. The spectral and chemical evidence indicated that the structural difference between territrem C and territrem B (C29H34O9) was in their phenyl moieties: a 4-hydroxy-3,5-dimethoxy phenyl group in territrem C and a 3,4,5-trimethoxy phenyl group in territrem B. It was also demonstrated that territrem B was obtained by methylation of territrem C with dimethyl sulfate.

Territrem B (TRB) is a fungal metabolite isolated from Aspergillus terreus shown previously to be a potent and irreversible inhibitor of acetylcholinesterase (AChE). In the present study, a number of binding and inhibition assays were carried out to further characterize the inhibitory effect of TRB. The results indicate that the binding of TRB (a) is much more selective than a well characterized selective inhibitor of AChE, BW284C51, (b) adopts a one-to-one stoichiometry with the enzyme, (c) cannot be undone by an AChE-regenerating oxime agent, which contrasts the ability of 8 M urea to release AChE-bound TRB, (d) is enhanced by high concentration NaCl but prevented, unless preincubated, by Triton X-100, and (e) exhibits quasi-first order kinetics with an overall inhibition constant of 0.01 nM(-1) min(-1). Together these results suggest a very different irreversible binding (a noncovalent type) from that of the covalent type, which involves typical irreversible AChE inhibitors such as diisopropylfluorophosphate and neostigmine. According to the prediction of a molecular modeling study, the distinct AChE inhibitory characteristics of TRB may arise from the inhibitor being noncovalently trapped within a unique active-site gorge structure of the enzyme. It was predicted that an optimal TRB. AChE binding would position a narrowing connection of the TRB structure at a constricted area near the entrance of the gorge, thereby providing a structural basis for the observed irreversible binding.

Acetylcholinesterase is a critical enzyme that regulates neurotransmission by degrading the neurotransmitter acetylcholine in synapses of the nervous system. It is an important target for both therapeutic drugs that treat Alzheimer's disease and chemical warfare agents that cripple the nervous system and cause death through paralysis. The enzyme has both catalytic and peripheral sites to which inhibitors may bind. Structures of recombinant human acetylcholinesterase in complex with the natural product inhibitors dihydrotanshinone I and territrem B reveal dihydrotanshinone I binding that is specific to only the peripheral site and territrem B binding that spans both sites and distorts the protein backbone in the peripheral site. These inhibitors may function as important molecular templates for therapeutics used for treatment of disease and protection against nerve agents.