Genome-wide analysis of Saccharomyces cerevisiae identifies cellular processes affecting intracellular aggregation of Alzheimer's amyloid-β42: importance of lipid homeostasis

Amyloid-β (Aβ)-containing plaques are a major neuropathological feature of Alzheimer's disease (AD). The two major isoforms of Aβ peptide associated with AD are Aβ40 and Aβ42, of which the latter is highly prone to aggregation. Increased presence and aggregation of intracellular Aβ42 peptides is an early event in AD progression. Improved understanding of cellular processes affecting Aβ42 aggregation may have implications for development of therapeutic strategies. Aβ42 fused to green fluorescent protein (Aβ42-GFP) was expressed in ∼4600 mutants of a Saccharomyces cerevisiae genome-wide deletion library to identify proteins and cellular processes affecting intracellular Aβ42 aggregation by assessing the fluorescence of Aβ42-GFP. This screening identified 110 mutants exhibiting intense Aβ42-GFP-associated fluorescence. Four major cellular processes were overrepresented in the data set, including phospholipid homeostasis. Disruption of phosphatidylcholine, phosphatidylserine, and/or phosphatidylethanolamine metabolism had a major effect on intracellular Aβ42 aggregation and localization. Confocal microscopy indicated that Aβ42-GFP localization in the phospholipid mutants was juxtaposed to the nucleus, most likely associated with the endoplasmic reticulum (ER)/ER membrane. These data provide a genome-wide indication of cellular processes that affect intracellular Aβ42-GFP aggregation and may have important implications for understanding cellular mechanisms affecting intracellular Aβ42 aggregation and AD disease progression.

The selective enzymatic synthesis of lipophilic esters of swainsonine

The potent and specific inhibitor of Golgi alpha-mannosidase II, swainsonine (SW) has been isolated in high yield from Swainsona procumbens and derivatised by regiospecific enzymatic reactions. In this study the regioselectivity of three commercially available enzymes, subtilisin Carlsberg, porcine pancreatic lipase (PPL) and Candida cylindracea lipase was determined for the acylation of swainsonine in predominantly anhydrous organic medium. The use of subtilisin in pyridine facilitated the single step synthesis of 2-O-butyryl-SW in a 23% yield, whilst catalysis by PPL in tetrahydrofuran gave 2-O-butyryl-SW (6%) and 1,2-di-O-butyryl-SW (31%).