Department of Biotechnology
inStem (Institute for Stem Cell Science and Regenerative Medicine)

Stochastic steps in secondary active sugar transport.

Publication Type

Research Support, N.I.H., Extramural

Date of Publication

July 5, 2016

Journal

Proceedings of the National Academy of Sciences of the United States of America

Volume/Issue

113/27

ISSN

1091-6490

Secondary active transporters, such as those that adopt the leucine-transporter fold, are found in all domains of life, and they have the unique capability of harnessing the energy stored in ion gradients to accumulate small molecules essential for life as well as expel toxic and harmful compounds. How these proteins couple ion binding and transport to the concomitant flow of substrates is a fundamental structural and biophysical question that is beginning to be answered at the atomistic level with the advent of high-resolution structures of transporters in different structural states. Nonetheless, the dynamic character of the transporters, such as ion/substrate binding order and how binding triggers conformational change, is not revealed from static structures, yet it is critical to understanding their function. Here, we report a series of molecular simulations carried out on the sugar transporter vSGLT that lend insight into how substrate and ions are released from the inward-facing state of the transporter. Our simulations reveal that the order of release is stochastic. Functional experiments were designed to test this prediction on the human homolog, hSGLT1, and we also found that cytoplasmic release is not ordered, but we confirmed that substrate and ion binding from the extracellular space is ordered. Our findings unify conflicting published results concerning cytoplasmic release of ions and substrate and hint at the possibility that other transporters in the superfamily may lack coordination between ions and substrate in the inward-facing state.

Alternate Journal

Proc Natl Acad Sci U S A

PubMed ID

27325773

PubMed Central ID

PMC4941443

Authors

Joshua L Adelman
Chiara Ghezzi
Paola Bisignano
Donald D F Loo
Seungho Choe
Jeff Abramson
John M Rosenberg
Ernest M Wright
Michael Grabe

Keywords

Molecular Dynamics Simulation
Sodium
Markov Chains
Monte Carlo Method
Patch-Clamp Techniques
Sodium-Glucose Transporter 1
Humans
HEK293 Cells
Glucose