Polyglutamine peptides form protofibrils composed by beta-sheets.The aggregation of these protofibrils causes amyloidosis.It was not yet clear how polyglutamine chains aggregate and form beta-sheets.For probing polyglutamine conformation in the beta-sheets,we performed all-atom molecular dynamics simulations on pairs of the polyglutamine fragments in explicit water which consist of 10 repeated glutamine residues from parallel,perpendicular,and anti-parallel initial conditions.Our results shows that the simulation formed anti-parallel beta-sheets and the number of beta-bridges increased gradually.It indicates that polyglutamine dimer prefer anti-parallel beta-sheet conformation than parallel conformation.This agrees well with previous researches by experiments and a coarse-grained molecular dynamics simulation.A free-energy barrier was also found at the structures with no beta-bridge,which makes the transformation between parallel and anti-parallel beta-sheets difficult.