Glutamine-binding　protein　(G1nBp)　is　one　of　the　ligand-specific　periplasmic　binding　proteins　in　the　Escherichia　coli　permease　systems,　predicted　to　play　an　important　role　in　transferring　Gin　from　the　periplasmic　space　to　the　cytoplasmic　space.　In　this　paper,　the　interaction　of　the　key　residues　in　G1nBp　with　the　ligand　Gin　and　the　functional　difference　between　the　two　hinges　in　G1nBp　were　evaluated　through　molecular　dynamics　simulation　sampling,　and　the　binding　free　energy　of　G1nBp　with　Gin　was　calculated　by　the　MM-PBSA　method.　The　results　show　that　the　main　impetus　to　bind　Gin　lies　in　the　van　der　Waals＇(VDW)　interactions　between　Gin　and　Phe13,　Phe50,　Thr118,　Ile69,　as　well　as　the　electrostatic　interactions　between　Arg75,　Thr70,　Asp157,　Gly68,　Lysl15,　Ala67,　His156　and　ligand　Gin.　The　hinge　region　85　similar　to　89　whose　fluctuation　is　larger　than　the　hinge　region　181　similar　to　185　has　a　more　flexibility　which　can　provide　a　structural　basis　to　bind　ligand　Gin,　while　the　main　function　of　the　hinge　region　181　similar　to　185　was　proposed　to　restrict　ligand　Gin　in　the　pocket　of　G1nBp.　It　is　found　that　the　result　predicted　with　the　MM-PBSA　method　agrees　well　with　experimental　data.　The　relationship　between　the　structure　and　function　of　G1nBp　is　well　illustrated,　which　provides　us　with　some　important　structural　information　on　the　open-close　mechanism　of　G1nBp　and　the　transportation　of　Gin.