ATP Binding to the Motor Domain from an ABC Transporter Drives Formation of a Nucleotide Sandwich Dimer

Abstract

It has been proposed that the reaction cycle of ATP binding cassette (ABC) transporters is driven by dimerization of their ABC motor domains upon binding ATP at their mutual interface. However, no such ATP sandwich complex has been observed for an ABC from an ABC transporter. In this paper, we report the crystal structure of a stable dimer formed by the E171Q mutant of the MJ0796 ABC, which is hydrolytically inactive due to mutation of the catalytic base. The structure shows a symmetrical dimer in which two ATP molecules are each sandwiched between the Walker A motif in one subunit and the LSGGQ signature motif in the other subunit. These results establish the stereochemical basis of the power stroke of ABC transporter pumps.

The motor domains of ABC-transporters

“…The Rad50cd-like dimer was convincingly shown to be physiologically correct when Hunt and coworkers presented their structure of the MJ0796 dimer with ATP bound as substrate (Smith et al 2002). In order to obtain such a structure, the authors crystallized a mutant of the NBD (E171Q), which shows no detectable ATP hydrolysis of the bound ATP and thus produced a stable dimer.…”

ATP-sensitive K channel channel/enzyme multimer: Metabolic gating in the heart

“…In the structure of the NBD2 monomer of SUR2A [14] as well as other ABC members, the ATP-binding site is exposed, suggesting that the catalytic site can be completed by interaction with another domain [51,66,67]. Evidence of physical proximity of NBDs [68] has hinted that one NBD monomer could complete the binding pocket of the adjacent one.…”

“…However, this finding implicates a different topology of signature and Walker motifs within a NBD dimer, making it difficult to generalize a single dimer structure to all ABC proteins [66]. Furthermore, in the presence of nucleotide, the biochemical or structural evidence of dimer formation was obtained only for Rad50 but not for ABC transporters [41,67]. Implementation of Rad50 architecture as a template for modeling of other ABC structures is limited, since in contrast to conventional ABC transporters Rad50 lacks membrane spanning domains and interacts with nucleotides via regions that are not conserved among ABC proteins [41,67].…”

“…Furthermore, in the presence of nucleotide, the biochemical or structural evidence of dimer formation was obtained only for Rad50 but not for ABC transporters [41,67]. Implementation of Rad50 architecture as a template for modeling of other ABC structures is limited, since in contrast to conventional ABC transporters Rad50 lacks membrane spanning domains and interacts with nucleotides via regions that are not conserved among ABC proteins [41,67]. The most recent crystal structure of MJ0796 obtained with the highest resolution of any NBD nucleotide-sandwich dimer allowed modeling of the SUR1 NBD dimer on the basis of sequence alignment [77].…”

“…External circle (clear elements) represents the second binding pocket comprised by the counterparts of NBD1 and NBD2. The scheme is developed based on sequence alignment between NBDs of SUR and MJ0796 protein [67,77]. In the compartmentalized cellular environment changes in cellular energetics can be transmitted over diffusion barriers, amplified and decoded as a signal by membrane metabolic sensor which triggers adaptive response adjusting energy demand and preserving, thereby, cellular well-being.…”