Single amino acid mutations in amyloid-beta (A beta) peptides can lead to early onset and increased severity of Alzheimer's disease. An example is the Osaka mutation (A beta(1-40)E22D), which is more toxic than wild-type A beta(1-40). This mutant quickly forms early stage fibrils, one of the hallmarks of the disease, and these fibrils can even seed fibrilization of wild-type monomers. Using molecular dynamic simulations, we show that because of formation of various intra- and intermolecular salt bridges the Osaka mutant fibrils are more stable than wild-type fibrils. The mutant fibril also has a wider water channel with increased water flow than the wild type. These two observations can explain the higher toxicity and aggregation rate of the Osaka mutant over the wild type.