This is a heptapeptide from the N-terminal prion-determining domain of the yeast protein Sup35 that forms amyloid fibrils. The availability of its detailed atomic oligomeric structure makes it a good model for studying the early stage of aggregation. The GNNQQNY dimer forms three stable sheet structures. in-register parallel, off-register parallel, and anti-parallel. The in-register parallel dimer, which is close to the amyloid beta-sheet structure, has few interpeptide hydrogen bonds, making hydrophobic interactions more important and increasing the conformational entropy compared to the anti-parallel sheet.