Table 1. Expression constructs used in this study.

Name	Expression construct	Experiment
Wild-type SERT	Full-length human SERT with a C-terminal thrombin-GFP-StrepII-His10 tag.	[3H] 5-HT transport assays
∆N72/ ∆C13 SERT	Wild-type SERT modified by deletion of 72 residues on N-term and 13 residues on C-term	Cryo-electron microscopy
ts2-inactive	Full-length SERT with thrombin cleavage sites inserted after Gln76 and Thr618 and carrying the Tyr110Ala, Ile291Ala thermostabilizing mutations with additional mutations of surface-exposed cysteines Cys554, Cys580, and Cys622 to alanine	X-ray crystallography and [3H] citalopram binding assays
ts2-active	Full-length SERT with thrombin cleavage sites inserted after Gln76 and Thr618 and carrying the Ile291Ala, Thr439Ser thermostabilizing mutations with additional mutations of surface-exposed cysteines Cys554, Cys580, and Cys622 to alanine	[3H] citalopram binding assays
Asn177 mutants	Asn177 mutated to either Val, Thr, or Gln in ts2-active background	[3H] citalopram binding assays