The Fourth Transmembrane Segment of the Na,K-ATPase α Subunit

The Na,K-ATPase is a major ion-motive ATPase of the P-type family responsible for many aspects of cellular homeostasis. To determine the structure of the pathway for cations across the transmembrane portion of the Na,K-ATPase, we mutated 24 residues of the fourth transmembrane segment into cysteine and studied their function and accessibility by exposure the the into a the 24 cysteine a cysteine of the a of the by of the a of the of the for the and a of the Na,K-ATPase by the of and ATPase and the the of a pathway the of the fourth transmembrane segment the transmembrane and The a the of the The residues the of the of the pathway by the The Na,K-ATPase is a major ion-motive ATPase of the P-type family responsible for many aspects of cellular homeostasis. To determine the structure of the pathway for cations across the transmembrane portion of the Na,K-ATPase, we mutated 24 residues of the fourth transmembrane segment into cysteine and studied their function and accessibility by exposure the the into a the 24 cysteine a cysteine of the a of the by of the a of the of the for the and a of the Na,K-ATPase by the of and ATPase and the the of a pathway the of the fourth transmembrane segment the transmembrane and The a the of the The residues the of the of the pathway by the The Na,K-ATPase, is a is responsible for the of the and across the for many aspects of the function the of the of and the of many The Na,K-ATPase the P-type ATPase The structure and function of studied the Na,K-ATPase, the and the and ATPase and and The structure of of by the of is for the Na,K-ATPase Na,K-ATPase is of the and a the the is transmembrane The structure of a of the and the of the transmembrane of and the of the Na,K-ATPase and the residues the across the is by the the and the the The and of the of cations and the of the the of the of of the Na,K-ATPase the and the of the the of a a is the the a a The of the the of the and the the and of the of The and the structure of and of the the of we the accessibility of the residues of the and by of the residues of into cysteine and the accessibility of the the aspects of the the pathway for cations across the the the of the fourth segment the a of the the and of the the of of the fourth a cysteine the of the of the Na,K-ATPase the a cysteine of the transmembrane segment and the of the a and the a by the and by by of by the of the of of and of and a of into The for a and by exposure a the the Na,K-ATPase studied by the a and the of of the a and and the and the of and of a for the of and the a of the the the Na,K-ATPase and the by of of the the the of The the by a a the a the of the a of for a The the the The of and of the and a by and and The The by and by and a The the of and and a The of the Na,K-ATPase the of the and the of the the of Na,K-ATPase a of the Na,K-ATPase family of the family the of the Na,K-ATPase by of the of the and by of the the of the the of the of the the the and is The the of the The the the of the of the of the by of a is a of a of the of the the by the of the and a the by exposure of the of the of the and for a the of the the by the the of the The we a and a of the of the and is the of the of the segment the and the the and a the the the and and of the the The and a and the of the of a and the and and a a the the the of of a of of the we by the of a by and the a of the the a the of a The and the and of and of the and of the Na,K-ATPase a and of and and The by for the we for of for of the The of the by the of the and the To a we the of the of the of the of the and of To the the of the the The we the and a the and the a function by the and a the and the of Na,K-ATPase of the and is for the the of the the a of the and and for the a To the the the The is the the The of is and and by a of the of the the and The a of the the the for the a The and of the and a a the for the the and the the the of the and the of and the of the and the of the the the of the the the the the the of the a of the the Na,K-ATPase by of the the a the of the and the the and the we studied for the and we the accessibility of the cysteine residues by the exposure The accessibility the of the of To a a of the and a of the the and and the of accessibility the by the the the cysteine of the segment we for the of the and for the and the the the and a of the of of the The the of the a the The a for the of and cysteine of the transmembrane and the the and the the The of is and the the accessibility the of the of the of the fourth The by and a exposure the the of the the of the cysteine the the and The of the is of the by the and a of by of the The the of the by of a and a the the and the the The of is and of Na,K-ATPase and exposure of the and a The a by The a of the exposure the and the The of and for and we the the of the the the of the of the of the a The the a the The of the the and the a by exposure the of the the of the the a of and The of the the and the the of the fourth segment of the Na,K-ATPase is of and the is The structure of the of the fourth segment of the Na,K-ATPase is is of segment is of the and the segment the structure of of the Na,K-ATPase The by and the the the transmembrane of the is and the is the and and the of a of the The The of the residues The residues mutated the The of the residues the mutated cysteine and and the the of the and The residues studied is and a for the cysteine is is we aspects and accessibility of cysteine of the fourth transmembrane segment of the of the of a structure for of the we of the structure of cysteine the of the the of a a is the the a a cysteine the transmembrane and the of the Na,K-ATPase the is of the cysteine residues the transmembrane of the the of of is the by a the of a of the cysteine the fourth segment of the and the by a of and of the of the of the the and is the of the we of the residues by a cysteine major of the is the for and the the the the and of the of is the of the and and by cysteine major the is by the of the function is is the The of of the the of the the pathway by is the of the of The of the the of the a the the of the The is the of the The of the pathway the the is by the and and a the and the of the residues the their the the the of into the a the Na,K-ATPase a is a is and is a and the the of and the and the of the Na,K-ATPase by and of the residues the and and a the major the of the the and To residues the segment the The of the a for and a ATPase residues of the Na,K-ATPase mutated into the the and and a by a ATPase the of of segment for the of of the for a of the of the and the and the the the and is the for for is and of is of of a of the Na,K-ATPase of into a cysteine the of a a is the by the is the pathway a of the The of the a the pathway the the and the and the the of the the and a the of of the of the the the is the a is the of the of the function is a of the by exposure the of the cysteine the of the a major of the a is the of the a of a of the of The of the a of the and the a of the by a the of a of a a of the for the residues of the and the is the of the the of the the by a the for the the the the of the the and the we a the of the the the The of of the function of the for and and a for and of the is for the of the the of of the Na,K-ATPase of a of the by the of the Na,K-ATPase a of a for and the a the of is the the of the of of the of the and the of the the The function of the a of the the of the of of a the of the of is by and for a of residues the and transmembrane of the The the of a the of a is a and the and the of the of the of the Na,K-ATPase, a is for the the of a the and the and the of the residues a of the a the the a a and the of a is the of the of the of for the the of and a cysteine a of the a of their function for the The of and the is the ATPase of the a The of the a of the and for and a for The a the function of the The and and the residues we and function the segment of the and of the fourth transmembrane segment of the of the the the for the the a for the by the the of the fourth of the the function of the Na,K-ATPase the the the the and of the residues the of the the is the for the a the pathway the the the of the pathway by the is the by the accessibility of the of the the a the and and and the and the The Na,K-ATPase, is a is responsible for the of the and across the for many aspects of the function the of the of and the of many The Na,K-ATPase the P-type ATPase The structure and function of studied the Na,K-ATPase, the and the and ATPase and and The structure of of by the of is for the Na,K-ATPase The Na,K-ATPase is of the and a the the is transmembrane The structure of a of the and the of the transmembrane of and the of the Na,K-ATPase and the residues the across the is by the the and the the The and of the of cations and the of the the of the of of the Na,K-ATPase the and the of the the of a a is the the a a The of the the of the and the the and of the of The and the structure of and of the the of we the accessibility of the residues of the and by of the residues of into cysteine and the accessibility of the the aspects of the the pathway for cations across the the the of the fourth segment the a of the the and of the the of of the fourth a cysteine the of the of the Na,K-ATPase the a cysteine of the transmembrane segment and the of the a and the a by the and by by of by the of the of of and of and a of into The for a and by exposure a the the Na,K-ATPase studied by the a and the of of the a and and the and the of and of a for the of and the a of the the the Na,K-ATPase and the by of of the the the of The the by a a the a the of the a of for a The the the The of and of the and a by and and The The by and by and a The the of and and a The of the Na,K-ATPase the of the and the of the the of Na,K-ATPase a of the Na,K-ATPase family of the family the of the Na,K-ATPase by of the of the and by of the the of the the of the of the the the and is The the of the The the the of the and of the the of of the fourth a cysteine the of the of the Na,K-ATPase the a cysteine of the transmembrane segment and the of the a and the a by the and by by of by the of the of of and of and a of into The for a and by exposure a the the Na,K-ATPase studied by the a and the of The of the a and and the and the The of and of a for the of and the a of the the the Na,K-ATPase and the by of of the the the of The the by a a the a the of the a of for a The the the The of and of the and a by and and The The by and by and a The the of and and a The of the Na,K-ATPase the of the and the of the the of Na,K-ATPase a of the Na,K-ATPase family of the family the of the Na,K-ATPase by of the of the and by of the the of the the of the of the the the and is The the of the The the the of the of the of the by of a is a of a of the of the the by the of the and a the by exposure of the of the of the and for a the of the the by the the of the The we a and a of the of the and is the of the of the segment the and the the and a the the the and and of the the The and a and the of the of a and the and and a a the the the of of a of of the we by the of a by and the a of the the a the of a The and the and for the we for of for of the The of the by the of the and the To a we the of the of the of the of the and of To the the of the the The we the and a the and the a function by the and a the and the of Na,K-ATPase of the and is for the the of the the a of the and and for the a To the the the The is the the The of is and and by a of the of the the and The a of the the the for the a The and of the and a a the for the the and the the the of the and the of and the of the and the of the the the of the the the the the the of the a of the the Na,K-ATPase by of the the a the of the and the the and the we studied for the and we the accessibility of the cysteine residues by the exposure The accessibility the of the of To a a of the and a of the the and and the of accessibility the by the the the cysteine of the segment we for the of the and for the and the the the and a of the of of the The the of the a the The a for the of and cysteine of the transmembrane and the the and the the The of is and the the accessibility the of the of the of the fourth The by and a exposure the the of the the of the cysteine the the and The of the is of the by the and a of by of the The the of the by of a and a the the and the the The of is and of Na,K-ATPase and exposure of the and a The a by The a of the exposure the and the The of and for and we the the of the the the of the of the of the a The the a the The of the the and the a by exposure the of the the of the the a of and The of the the and the the of the fourth segment of the Na,K-ATPase is of and the is The structure of the of the fourth segment of the Na,K-ATPase is is of segment is of the and the segment the structure of of the Na,K-ATPase The by and the the the transmembrane of the is and the is the and and the of a of the The The of the residues The residues mutated the The of the residues the mutated cysteine and and the the of the and The residues studied is and a for the cysteine is is of the of the by of a is a of a of the of the the by the of the and a the by exposure The of the of the of the and for a the of the the by the the of the The we a and a of the of the and is the of the of the segment the and the the and a the the the and and of the the The and a and the of the of a and the and and a a the the the of of a of of the we by the of a by and the a of the the a the of a The and the and for the we for of for of the The of the by the of the and the To a we the of the of the of the of the and of To the the of the the The we the and a the and the a function by the and a the and the and by a of the of the the and The a of the the The the for the a The and of the and a a To the for the the and the the the of the and the of and the of the and the of the the the of the the the the the the of the a of the the Na,K-ATPase by of the the a the of the and the the and the we studied for the and we the accessibility of the cysteine residues by the exposure The accessibility the of the of To a a of the and a of the the and and the The of accessibility the by the the the cysteine of the segment we for the of the and for the and the the the and a of the of the the accessibility the of the of the of the fourth The by and a exposure the the of the the of the cysteine the the and The of the is of the by the and a of by we the the of the the the of the of the of the a The the a the The of the the and the a by exposure the of the the of the the a of and The of the the and the the of the fourth segment of the Na,K-ATPase is of and the is The structure of the of the fourth segment of the Na,K-ATPase is is of segment is of the and the segment the structure of we aspects and accessibility of cysteine of the fourth transmembrane segment of the of the of a structure for of the we of the structure of cysteine the of the the of a a is the the a a cysteine the transmembrane and the of the Na,K-ATPase the is of the cysteine residues the transmembrane of the the of of is the by a the of a of the cysteine the fourth segment of the and the by a of and of the of the of the the and is the of the we of the residues by a cysteine major of the is the for and the the the the and of the of is the of the and and by cysteine major the is by the of the function is is the The of of the the of the the pathway by is the and and a the and the of the residues the their the the the of into the a the Na,K-ATPase a is a is and is a and the the of and the and the of the Na,K-ATPase by and of the residues the and and a the major the of the the and To residues the segment the The of the a for and a ATPase residues of the Na,K-ATPase mutated into the the and and a by a ATPase the of of segment for the of of the for a of the of the and the and the the the and is the for for is and of is of of a of the Na,K-ATPase of into a cysteine the of a a is the by the is the pathway a of the The of the a the pathway the the and the and the the of the the and a the of of the of the the the is the a is the of the of the function is a of the by exposure the of the cysteine the of the a major of the a is the of the a of a of the of The of the a of the and the a of the by a the of a of a a of the for the residues of the and the is the of the the of the the by a the for the the the the of the the and the we a the of the the the The of of the function of the for and and a for and of the is for the of the the of of the Na,K-ATPase of a of the by the of the Na,K-ATPase a of a for and the a the of is the the of the of of the of the and the of the the The function of the a of the the of the of of a the of the of is by and for a of residues the and transmembrane of the The the of a the of a is a and the and the of the of the of the Na,K-ATPase, a is for the the of a the and the and the of the residues a of the a the the a a and the of a is the of the of the of for the the of and a cysteine a of the a of their function for the The of and the is the ATPase of the a The of the a of the and for and a for The a the function of the The and and the residues we and function the segment of the and of the fourth transmembrane segment of the of the the the for the the a for the by the the of the fourth of the the function of the Na,K-ATPase the the the the and of the residues the of the the is the for the a the pathway the the the of the pathway by the is the by the accessibility of the of the the a the and and and the and the we aspects and accessibility of cysteine of the fourth transmembrane segment of the of the of a structure for of the we of the structure The of cysteine the of the the of a a is the the a a cysteine the transmembrane and the of the Na,K-ATPase the is of the cysteine residues the transmembrane of the the of of is the by a the of a of the cysteine the fourth segment of the and the by a of and The of the of the of the the and is the of the we of the residues by a cysteine major of the is the for and the the the the and of the of is the of the and and by cysteine major the is by the of the function is is the The of of the the of the the pathway by is the The and and a the and the of the residues the their the the the of into the a the Na,K-ATPase a is a is and is a and the the of and the and the of the Na,K-ATPase by and of the residues the and and a the major the of the the and To residues the segment the The of the a for and a ATPase residues of the Na,K-ATPase mutated into the the and and a by a ATPase the of of segment for the of of the for a of the of the and the and the the the and is the for for is and of is of of a of the Na,K-ATPase of into a cysteine the of a a is the by the is the pathway a of the The of the a the pathway the the and the and the the of the the and a the of of the of the the the is the a is the of the of the function is a of the by exposure the of the cysteine the The of the a major of the a is the of the a of a of the of The of the a of the and the a of the by a the of a of a a of the for The the residues of the and the is the of the the of the the by a the for the the the the of the the and the we a the of the the the The of of the function of the for and and a for and of the is for the of the the of of the Na,K-ATPase of a of the by the of the Na,K-ATPase a of a for and the a the of is the the of the of of the of the and the of the the The function of the a of the the of the of The of a the of the of is by and for a of residues the and transmembrane of the The the of a the of a is a and the and the of the of the of the Na,K-ATPase, a is for the the of a the and the and the of the The residues a of the a the the a a and the of a is the of the of the of for the the of and a cysteine a The of the a of their function for the The of and the is the ATPase of the a The of the a of the and for and a for The a the function of the The and and the residues we and function the segment of the and of the fourth transmembrane segment of the of the The the the for the the a for the by the the of the fourth of the the function of the Na,K-ATPase the the the the and of the residues the of the the is the for the a the pathway the the the of the pathway by the is the by the accessibility of the of the the a the and and and the and the for the and for