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The iron-transport glycoprotein transferrin has recently been shown to serve as a potent inhibitor of Aβself-association. Although this novel, to our knowledge, inhibitory function of transferrin is of potential therapeutic interest for the treatment of Alzheimer’s disease, the underlying mechanism is still not fully understood. Although it has been shown that the Fe(III) sequestration by transferrin reduces oxidative damage and Aβaggregation, it is not clear whether transferrin is also able to inhibit Aβself-association through direct binding of Aβ. Here, using saturation transfer and off-resonance relaxation NMR spectroscopy, we show that transferrin inhibits Aβaggregation also by preferentially binding Aβoligomers and outcompeting Aβmonomers that would otherwise cause the growth of the Aβoligomers into larger assemblies. This inhibitory mechanism is different from the iron-sequestration model, but it is qualitatively similar to a mechanism previously proposed for the inhibition of Aβself-association by another plasma and cerebrospinal fluid protein, i.e.,human serum albumin. These results suggest that Aβmonomer competition through direct Aβoligomer binding might be a general strategy adopted by proteins in plasma and cerebrospinal fluid to prevent Aβaggregation.

Human serum albumin (HSA) is not only a fatty acid and drug carrier protein, it is also a potent inhibitor of Aβself-association in plasma. However, the mechanism underlying the inhibition of Aβfibrillization by HSA is still not fully understood. We therefore investigated the Aβ-HSA system using a combined experimental strategy based on saturation transfer difference (STD) NMR and intrinsic albumin fluorescence experiments on three Aβpeptides with different aggregation propensities (i.e., Aβ(12–28), Aβ(1–40), and Aβ(1–42)). Our data consistently show that albumin selectively binds to cross-β-structured Aβoligomers as opposed to Aβmonomers. The HSA/Aβoligomer complexes have KDvalues in the micromolar to submicromolar range and compete with the further addition of Aβmonomers to the Aβassemblies, thus inhibiting fibril growth (“monomer competitor” model). Other putative mechanisms, according to which albumin acts as a “monomer stabilizer” or a “dissociation catalyst”, are not supported by our data, thus resolving previous discrepancies in the literature regarding Aβ-HSA interactions. In addition, the model and the experimental approaches proposed here are anticipated to have broad relevance for the characterization of other systems that involve amyloidogenic peptides and oligomerization inhibitors.

Three eremophilane sesquiterpenes (1, 2, and 3) were isolated from Penicillium roquefortiDAOM 232127, and their structures were established. The new (3S)-3-acetoxyeremophil-1(2),7(11),9(10)-trien-8-one (3) is a likely biosynthetic precursor of PR toxin. 1-Hydroxyeremophil-7(11),9(10)-dien-8-one (1) is related to the immunosuppressant cuspidatol. The application of semihyphenated LC-MS-SPE/NMR to rapidly identify, purify, and elucidate the structures of 1, 2, and 3is described.