Cooperative, ATP-dependent association of the nucleotide binding cassettes during the catalytic cycle of ATP-binding cassette transporters.

摘要: ATP-binding cassette (ABC) transporters harvest the energy present in cellular ATP to drive translocation of a structurally diverse set solutes across membrane barriers eubacteria, archaebacteria, and eukaryotes. The positively cooperative ATPase activity (Hill coefficient, 1.7) model soluble known structure, MJ0796, fromMethanococcus jannaschii indicates that at least two binding sites participate catalytic reaction. Mutation base E171Q, produced can bind but not efficiently hydrolyze ATP. equivalent mutation (E179Q) homologous cassette, MJ1267, had an identical effect. Both mutant cassettes formed dimers presence ADP, indicating is first coupled transport cycle through domain association non-hydrolyzable nucleotides adenosine 5′-(β,γ-imino)triphosphate 5′-3-O-(thio)triphosphate were poor analogues terms their ability promote dimerization. Moreover, inclusion MgCl2, substitution KCl for NaCl, or alterations polarity side chain all weakened ATP-dependent dimer, suggesting electrostatic interactions are critical Thus, upon hydrolysis bound release product, both conformational changes apart, providing second opportunity couple free