The formation of β-amyloid fibrils is a critical step in the pathogenesis of Alzheimer's disease. This study shows that a pentapeptide ligand, KLVFF (corresponding to Aβ 16-20), can bind to full-length Aβ and prevent its assembly into amyloid fibrils. Alanine scanning revealed that amino acids Lys16, Leu17, and Phe20 are critical for binding and inhibition of Aβ fibril formation. A mutant Aβ molecule with these residues substituted had a significantly reduced ability to form amyloid fibrils, suggesting that Aβ 16-20 serves as a binding sequence during polymerization and fibril formation. The KLVFF peptide may serve as a lead compound for developing agents that inhibit Aβ amyloidogenesis in vivo. Alzheimer's disease is characterized by the deposition of amyloid in the brain. The basic component of amyloid is a peptide called Aβ, a proteolytic fragment of the Alzheimer amyloid precursor protein (APP). Aβ amyloid is central to the pathogenesis of Alzheimer's disease, but the pathophysiological consequences of amyloid deposition are unclear. However, it has been suggested that Aβ polymers and amyloid are toxic to neurons, causing neurodegeneration. Previous studies indicate that Aβ polymerization in vivo and in vitro is a specific process involving interactions between binding sequences in the Aβ peptide. A rational pharmacological approach to prevent amyloid formation would be to use drugs that specifically interfere with Aβ-Aβ interactions and polymerization. The study hypothesized that ligands capable of binding to and blocking such sequences might inhibit amyloid fibril formation. The strategy was to identify binding sequences in Aβ and synthesize a peptide ligand based on their primary structures. The study identified binding sequences in the Aβ molecule using systematic synthesis of short peptides. The minimum length of an identified binding sequence was determined by truncating the peptide. Critical residues were identified by alanine scanning. These residues were then substituted in an Aβ fragment to determine their importance for Aβ amyloid fibril formation. The study also determined if the identified ligand could inhibit fibril formation of Aβ 1-40. The study used various techniques, including radioligand binding studies, surface plasmon resonance spectroscopy, and electron microscopy, to analyze the binding and polymerization of Aβ. The results showed that the KLVFF peptide could bind to Aβ and inhibit its fibril formation. The study concluded that the KLVFF peptide may serve as a lead compound for developing agents that inhibit Aβ amyloidogenesis in vivo.The formation of β-amyloid fibrils is a critical step in the pathogenesis of Alzheimer's disease. This study shows that a pentapeptide ligand, KLVFF (corresponding to Aβ 16-20), can bind to full-length Aβ and prevent its assembly into amyloid fibrils. Alanine scanning revealed that amino acids Lys16, Leu17, and Phe20 are critical for binding and inhibition of Aβ fibril formation. A mutant Aβ molecule with these residues substituted had a significantly reduced ability to form amyloid fibrils, suggesting that Aβ 16-20 serves as a binding sequence during polymerization and fibril formation. The KLVFF peptide may serve as a lead compound for developing agents that inhibit Aβ amyloidogenesis in vivo. Alzheimer's disease is characterized by the deposition of amyloid in the brain. The basic component of amyloid is a peptide called Aβ, a proteolytic fragment of the Alzheimer amyloid precursor protein (APP). Aβ amyloid is central to the pathogenesis of Alzheimer's disease, but the pathophysiological consequences of amyloid deposition are unclear. However, it has been suggested that Aβ polymers and amyloid are toxic to neurons, causing neurodegeneration. Previous studies indicate that Aβ polymerization in vivo and in vitro is a specific process involving interactions between binding sequences in the Aβ peptide. A rational pharmacological approach to prevent amyloid formation would be to use drugs that specifically interfere with Aβ-Aβ interactions and polymerization. The study hypothesized that ligands capable of binding to and blocking such sequences might inhibit amyloid fibril formation. The strategy was to identify binding sequences in Aβ and synthesize a peptide ligand based on their primary structures. The study identified binding sequences in the Aβ molecule using systematic synthesis of short peptides. The minimum length of an identified binding sequence was determined by truncating the peptide. Critical residues were identified by alanine scanning. These residues were then substituted in an Aβ fragment to determine their importance for Aβ amyloid fibril formation. The study also determined if the identified ligand could inhibit fibril formation of Aβ 1-40. The study used various techniques, including radioligand binding studies, surface plasmon resonance spectroscopy, and electron microscopy, to analyze the binding and polymerization of Aβ. The results showed that the KLVFF peptide could bind to Aβ and inhibit its fibril formation. The study concluded that the KLVFF peptide may serve as a lead compound for developing agents that inhibit Aβ amyloidogenesis in vivo.