4X2S:
reference: Transport domain unlocking sets the uptake rate of an aspartate transporter., Akyuz N, Georgieva ER, Zhou Z, Stolzenberg S, Cuendet MA, Khelashvili G, Altman RB, Terry DS, Freed JH, Weinstein H, Boudker O, Blanchard SC, Nature. 2015 Feb 5;518(7537):68-73. doi: 10.1038/nature14158. PMID: 25652997

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