Inhibitor binding mode and allosteric regulation of Na+-glucose symporters

Paola Bisignano,Matthew P Jacobson,Chakrapani Kalyanaraman,Michael Grabe,Chiara Ghezzi,Nicholas F Polizzi,Hyunil Jo,Rosmarie Friemann,Thorsten Althoff,Ernest M Wright

doi:10.1038/s41467-018-07700-1

Abstract

Sodium-dependent glucose transporters (SGLTs) exploit sodium gradients to transport sugars across the plasma membrane. Due to their role in renal sugar reabsorption, SGLTs are targets for the treatment of type 2 diabetes. Current therapeutics are phlorizin derivatives that contain a sugar moiety bound to an aromatic aglycon tail. Here, we develop structural models of human SGLT1/2 in complex with inhibitors by combining computational and functional studies. Inhibitors bind with the sugar moiety in the sugar pocket and the aglycon tail in the extracellular vestibule. The binding poses corroborate mutagenesis studies and suggest a partial closure of the outer gate upon binding. The models also reveal a putative Na+ binding site in hSGLT1 whose disruption reduces the transport stoichiometry to the value observed in hSGLT2 and increases inhibition by aglycon tails. Our work demonstrates that subtype selectivity arises from Na+-regulated outer gate closure and a variable region in extracellular loop EL5.

Highlights

Our approach was to carefully construct structural models of hSGLT1 and hSGLT2 based on the crystal structures of two bacterial homologs, vSGLT and SiaT, dock the sodium-dependent glucose transporter (SGLT) inhibitors into the homology models, and compare the docking poses with functional studies on SGLT mutant transporters
Our results reveal that the inhibitors bind to the Na+-bound, outward-facing conformation of hSGLT1 and hSGLT2 with the glucose moiety of the inhibitor in the sugar binding site and the aglycon tail in the external vestibule
The inhibitor binding site is remarkably similar for hSGLT1 and hSGLT2 in that the glucose moiety of the inhibitor, phlorizin and dapagliflozin, overlaps the glucose binding site (Figs. 1 and 2)

Summary

Introduction

Approved hSGLT2 inhibitors—glucosides containing a sugar moiety connected to an aromatic tail referred to as an aglycon—were shown to reduce heart failure hospitalization rates by 35% compared to other diabetes treatments while cutting deaths from any cause by 32%4. While very promising, these drugs are not free from side effects[5], and the lack of knowledge concerning the molecular determinants of action poses a barrier to developing new chemotypes with an improved therapeutic window.

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