In this paper first-principles calculations of Ni（111）/α-Al2O3（0001） interfaces have been performed, and are compared with the preceding results of the Cu （111）/α-Al2O3（0001） interface [2004 Phil. Mag. Left....In this paper first-principles calculations of Ni（111）/α-Al2O3（0001） interfaces have been performed, and are compared with the preceding results of the Cu （111）/α-Al2O3（0001） interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu（111）/α Al2O3（0001） interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni（111）/α-A1203（0001） interfaces is similar to that in the corresponding Cu（111）/α- Al2O3（0001） interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively.展开更多
P-glycoprotein(ABCB1)is the first discovered mammalian member of the large family of ATP binding cassette(ABC)transporters.It facilitates the movement of compounds(called allocrites)across membranes,using the energy o...P-glycoprotein(ABCB1)is the first discovered mammalian member of the large family of ATP binding cassette(ABC)transporters.It facilitates the movement of compounds(called allocrites)across membranes,using the energy of ATP binding and hydrolysis.Here,we review the thermodynamics of allocrite binding and the kinetics of ATP hydrolysis by ABCB1.In combination with our previous molecular dynamics simulations,these data lead to a new model for allocrite transport by ABCB1.In contrast to previous models,we take into account that the transporter was evolutionarily optimized to operate within a membrane,which dictates the nature of interactions.Hydrophobic interactions drive lipid-water partitioning of allocrites,the transport process’s first step.Weak dipolar interactions(including hydrogen bonding,π-π stacking,and π-cation interactions)drive allocrite recognition,binding,and transport by ABCB1 within the membrane.Increasing the lateral membrane packing density reduces allocrite partitioning but enhances dipolar interactions between allocrites and ABCB1.Allocrite flopping(or reorientation of the polar part towards the extracellular aqueous phase)occurs after hydrolysis of one ATP molecule and opening of ABCB1 at the extracellular side.Rebinding of ATP re-closes the transporter at the extracellular side and expels the potentially remaining allocrite into the membrane.The high sensitivity of the steady-state ATP hydrolysis rate to the nature and number of dipolar interactions,as well as to the dielectric constant of the membrane,points to a flopping process,which occurs to a large extent at the membrane-transporter interface.The proposed unidirectional ABCB1 transport cycle,driven by weak dipolar interactions,is consistent with membrane biophysics.展开更多
基金supported by Qianjiang Talent Project of Zhejiang Province of China (Grant No 2007R10028)the Science Foundation of Zhejiang Sci-Tech University (ZSTU) in China (Grant No 0613271-Y)Science Foundation of Zhejiang Province of China(Grant No Y407188)
文摘In this paper first-principles calculations of Ni（111）/α-Al2O3（0001） interfaces have been performed, and are compared with the preceding results of the Cu （111）/α-Al2O3（0001） interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu（111）/α Al2O3（0001） interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni（111）/α-A1203（0001） interfaces is similar to that in the corresponding Cu（111）/α- Al2O3（0001） interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively.
基金Stiftung zur Forderung der biologischen Forschung,Basel,Switzerland.
文摘P-glycoprotein(ABCB1)is the first discovered mammalian member of the large family of ATP binding cassette(ABC)transporters.It facilitates the movement of compounds(called allocrites)across membranes,using the energy of ATP binding and hydrolysis.Here,we review the thermodynamics of allocrite binding and the kinetics of ATP hydrolysis by ABCB1.In combination with our previous molecular dynamics simulations,these data lead to a new model for allocrite transport by ABCB1.In contrast to previous models,we take into account that the transporter was evolutionarily optimized to operate within a membrane,which dictates the nature of interactions.Hydrophobic interactions drive lipid-water partitioning of allocrites,the transport process’s first step.Weak dipolar interactions(including hydrogen bonding,π-π stacking,and π-cation interactions)drive allocrite recognition,binding,and transport by ABCB1 within the membrane.Increasing the lateral membrane packing density reduces allocrite partitioning but enhances dipolar interactions between allocrites and ABCB1.Allocrite flopping(or reorientation of the polar part towards the extracellular aqueous phase)occurs after hydrolysis of one ATP molecule and opening of ABCB1 at the extracellular side.Rebinding of ATP re-closes the transporter at the extracellular side and expels the potentially remaining allocrite into the membrane.The high sensitivity of the steady-state ATP hydrolysis rate to the nature and number of dipolar interactions,as well as to the dielectric constant of the membrane,points to a flopping process,which occurs to a large extent at the membrane-transporter interface.The proposed unidirectional ABCB1 transport cycle,driven by weak dipolar interactions,is consistent with membrane biophysics.
