A novel constrained peptide epitope derived from Αβ, wherein the eptitope comprises the amino acid sequence SNK, related antibody compositions and methods of use. An isolated antibody that specifically binds to a cyclic peptide comprising the conformational epitope which comprises the amino acid sequence SNK and corresponding to a solvent-exposed, antibody accessible knuckle region of oligomeric Αβ is described. An antigenic peptide comprising an epitope having a constrained cyclic configuration, which comprises the amino acid seqeuence SNK and corresponding to a solvent-exposed, antibody accessible knuckle region of oligomeric Αβ is also described. Methods of treating, preventing and diagnosing Alzheimers disease are also described.
