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
P-glycoprotein(P-gp or ABCB1)is a member of the broad family of ABC transporters.P-gp participates in the establishment of physiological barriers limiting cellular access of a large number of toxic compounds.It thus p...P-glycoprotein(P-gp or ABCB1)is a member of the broad family of ABC transporters.P-gp participates in the establishment of physiological barriers limiting cellular access of a large number of toxic compounds.It thus plays important roles in the pharmacokinetics of these compounds.Cancer cells and cells infected by viruses exploit the presence of P-gp to fend off drug treatment,rendering them multidrug-resistant.Overcoming multidrug resistance caused by expression of ABC transporters has gained increasing attention in the field of drug development.Recently,studies of P-gp,especially from structural investigations by both cryo-electron microscopy and X-ray crystallography,have provided high-resolution mechanistic details for the function of this transporter.Structures with increasing resolution and accuracy in various substrate-and inhibitor-bound forms are available for analysis and a consensus on the mechanism of substrate polyspecificity is emerging.The use of new structural information may aid development of P-gp inhibitors as well as compounds that may bypass P-gp action.展开更多
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.
基金This work was supported by the Intramural Research Program of the National Institutes of Health,National Cancer Institute,Center for Cancer Research.
文摘P-glycoprotein(P-gp or ABCB1)is a member of the broad family of ABC transporters.P-gp participates in the establishment of physiological barriers limiting cellular access of a large number of toxic compounds.It thus plays important roles in the pharmacokinetics of these compounds.Cancer cells and cells infected by viruses exploit the presence of P-gp to fend off drug treatment,rendering them multidrug-resistant.Overcoming multidrug resistance caused by expression of ABC transporters has gained increasing attention in the field of drug development.Recently,studies of P-gp,especially from structural investigations by both cryo-electron microscopy and X-ray crystallography,have provided high-resolution mechanistic details for the function of this transporter.Structures with increasing resolution and accuracy in various substrate-and inhibitor-bound forms are available for analysis and a consensus on the mechanism of substrate polyspecificity is emerging.The use of new structural information may aid development of P-gp inhibitors as well as compounds that may bypass P-gp action.