Transmembrane helix 7 in the Na+/dicarboxylate cotransporter 1 is an outer helix that contains residues critical for function

► TM7 of the Na+/dicarboxylate cotransporter 1 is likely to be an outer helix. ► Gly-356 was inhibited by MTSET but could not be labeled by the bulkier MTSEA-biotin. ► Phe-336 and Phe-339 are important for substrate turnover or selectivity. ► TM7 contains functionally important residues; cysteine mutants had reduced activity independent of protein expression.