(613a) Elucidating Mechanisms of Substrate Transport in Membrane Transporters 

Understanding the exchange of biological molecules across the phospholipid bilayer is of fundamental interest to the scientific community. In particular, transporters from the major facilitator superfamily (MFS) are involved in the transport of a wide spectrum of substrates across biomembranes and play a pivotal role in multiple physiological processes. Despite intense investigation, only few MFS proteins from six subfamilies have been structurally elucidated. Computational investigations have provided tremendous insights in the structure and function of these transporters. However, large scale unbiased simulations that could provide a molecular view of the complete transport cycle have not been reported. Here, we report development and application of novel computational methods for (a) enhanced unbiased sampling of the conformational landscape of membrane transporters and (b) optimal design of experimental probes for membrane protein dynamics. We demonstrate the application of these methods to investigate the transport cycle of the following membrane transporters: peptide transporter PepT_SO, nitrate transporter AtNRT1.1 and Sugar Transporter OsSWEET2b. These proteins have only one available crystal structure. Our results provide for the first time, the complete transport cycle of these key transporters including key conformational states along the transport pathway using large scale (100's of microseconds) molecular dynamics simulations.