Conformational changes in MetNI: steered molecular dynamic studies of the methionine ABC transporter with and without substrates

ATP-binding cassette (ABC) transporters are integral membrane proteins that utilised energy from ATP hydrolysis to translocate substrates across the membrane. In addition to the common nucleotide-binding domains (NBDs) and transmembrane domains (TMDs), the methionine ABC transporter has C-terminal regulatory domains (C2 domains) that belong to ACT protein family. When the amount of methionine in the cell is high, the transport stops. This phenomenon is called trans-inhibition. To understand how a trans-inhibited protein returns to an uninhibited, resting state, we performed steered molecular dynamic simulations with and without the substrates. From the simulations, we observed some important conformational changes in the whole ABC transporter, including the constriction in the translocation pathway in the TMDs and approach of the NBDs. However, the C2 domains behaved differently in two types of the simulations. These findings might help to explain the relationship of the conformational changes of the C2 domains with the rearrangements of the NBDs or TMDs, and provide a way to understand the trans-inhibition from an opposite direction.