3.A.1.135.5
The hetrodimeric ABC transporter, TM287/TM288.  The 2.9-Å crystal structure has been solved in the inward-facing state. The two nucleotide binding domains (NBDs) remain in contact through an interface involving conserved motifs that connect the two ATP hydrolysis sites.  AMP-PNP binds to a degenerate catalytic site which deviates from the consensus sequence in the same positions as the eukaryotic homologs, CFTR (TC# 3.A.1.202.1) and TAP1-TAP2 (TC# 3.A.1.209.1) (Hohl et al. 2012).  The structural basis for allosteric crosstalk (positive cooperativity) between the two ATP binding sites has been studied (Hohl et al. 2014).  The two NBDs exhibit unexpected differences and flexibility (Bukowska et al. 2015). It exports daunomycin and the nonfluorescent 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein-acetoxymethylester (BCECF-AM) (Hohl et al. 2012). Timachi et al. 2017 observed hydrolysis-independent closure of the NBD dimer, further stabilized as the consensus site nucleotide is committed to hydrolysis.