Structural insight into the substrate recognition and transport mechanism of the human LAT2–4F2hc complex
Renhong Yan, Jiayao Zhou, Yaning Li, Jianlin Lei, Qiang Zhou
Abstract
The l -type amino acid transporters (LATs) mediate neutral amino acids and thyroid hormones across membrane 1 , 2 , 3 , 4 , 5 . LAT2, which is mainly expressed in kidney and small intestine, has a broader substrate range than LAT1, including small amino acids 6 , 7 , 8 , 9 . LAT1 or LAT2 are the light chains of the heterodimeric amino acid transporters (HATs), which are composed of a light chain and a heavy chain. The 4F2 cell-surface antigen heavy chain (4F2hc) is the heavy chain for LAT1 and LAT2, playing roles in plasma membrane localization of LATs 4 and required for the stability and the transport activity of HATs 10 . The first cryo-EM structures of the human LAT1–4F2hc complex had been solved recently, but the native substrates bound structure of HATs still remains unknown. Here, we report the cryo-EM structures of the human LAT2–4F2hc complex bound with substrate Leu or Trp at resolution of 2.9 or 3.4 Å, respectively. These structures exhibit an inward-open conformation, similar to that of the human LAT1–4F2hc complex. The substrates Leu and Trp are all bound at the bottom of the inner pocket of the transporter, while Trp might adopt two different binding modes. Structural analysis and biochemical assays provide important basis for the working mechanism of HATs, especially by elucidating the substrate-binding mechanism.