New insights into GluT1 mechanics during glucose transfer

Abstract

Glucose plays a crucial role in the mammalian cell metabolism. In the erythrocytes and endothelial cells of the blood-brain barrier, glucose uptake is mediated by the glucose transporter type 1 (GluT1). GluT1 deficiency or mutations cause severe physiological disorders. GluT1 is also an important target in cancer therapy as it is overexpressed in tumor cells. Previous studies have suggested that GluT1 mediates solute transfer through a cycle of conformational changes. However, the corresponding 3D structures adopted by the transporter during the transfer process remain elusive. In the present work, we first elucidate the whole conformational landscape of GluT1 in the absence of glucose, using long molecular dynamics simulations and show that the transitions can be accomplished through thermal fluctuations. Importantly, we highlight a strong coupling between intracellular and extracellular domains of the protein that contributes to the transmembrane helices reorientation during the transition. The conformations adopted during the simulations differ from the known 3D bacterial homologs structures resolved in similar states. In holo state simulations, we find that glucose transits along the pathway through significant rotational motions, while maintaining hydrogen bonds with the protein. These persistent motions affect side chains orientation, which impacts protein mechanics and allows glucose progression.

Proton Control of Transitions in an Amino Acid Transporter

“…Indeed, the implicit assumption of many MD studies that local conformational changes observed in short simulations can provide insight into global motions has recently been called into question (42). It is clear that very long simulation times are often required, as recently demonstrated for the semiSWEET transporter (43) or the GluT1 transporter (44). Indeed, to study the complete conformation cycle, it would seem likely that the approach of Markov state modeling might be the most appropriate as recently demonstrated with PepT so transporter (45).…”

Proton-control of transitions in an amino-acid transporter

“…Indeed, the implicit assumption of many MD studies that local conformational changes observed in short simulations can provide insight into global motions has recently been called into question (35). It is clear that very long simulation times are often required, as recently demonstrated for the semiSWEET transporter (36) or the GluT1 transporter (37). Indeed, to study the complete conformation cycle, it would seem likely that the approach of Markov State Modelling (MSM) might be the most appropriate as recently demonstrated with PepT so transporter (38).…”

Conformational Transition Pathways in Major Facilitator Superfamily Transporters

“…6,23 The binding of inorganic phosphate facilitates the transition from the IF to OF states, and the replacement of glycerol-3-phosphate reverts the protein back to the IF conformation. 24,25 Molecular dynamics simulations have been a useful tool in the extensive study of proteins and membrane transporters such as GkPOT, 26 GluT1, 27 and GlpT. 28 Unfortunately, due to the short timescales of typical unbiased molecular dynamics simulations, this technique is often incapable of capturing large-scale conformational changes.…”

“…Recent work has shown a complete transition of GluT1 in 1-1.5 µs. 27 For slower IF-OF transitions, we have recently proposed a computational recipe that allows for reconstructing the IF-OF transition of various timescales. 28,31,32 We have recently improved this protocol by employing a Riemannian description of conformational landscape of protein.…”