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Talk- Sunny Hwang

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Protein-mediated transport of mercuric ions across the bacterial inner membrane

  • cmb seminar
When May 14, 2018
from 11:00 AM to 12:30 PM
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Mercury (Hg) is among the most toxic heavy metals because of its high affinity for sulfhydryl groups in amino acids. Mercury alters the structure of proteins after binding, often leading to a loss of function. Many bacteria take up mercury via members of the mercuric ion (mer) superfamily, i.e., a periplasmic Hg(II)scavenging protein (MerP) and one or more inner membrane­spanning proteins (MerC, MerF, and MerT), which transport Hg(II) into the cytoplasm. In all of these transporters, a pair of cysteine residues is predicted to reside within the inner membrane, with a second pair of cysteines on the cytoplasmic face. However, it is not clear how MerF, one of the smallest gene products known to constitute a transport system, can function as a transporter alone, or if the formation of a multimeric complex is necessary. Also, the effect of the different numbers of transmembrane regions is not known. In this project, we will use all-­atom and coarse-grained molecular dynamics (MD) simulations to provide molecular level insight into mercury transport mechanisms. With all atom simulations, we will investigate the interaction of the periplasmic metallochaperone MerP with the known mercuric ion transporters and MerF, and seek to identify possible pathways between them for transferring the ion. Replica exchange umbrella sampling (REUS), a widely used method to calculate free energy profiles of physical and/or chemical processes along predetermined reaction coordinates, will be used. Coarse grained approaches, in which small groups of atoms are treated as single particles, will allow us to expand the time scales of MD simulations of membranes with dozens of proteins to tens of microseconds. We will use this method to study the self assembly behavior of transmembrane proteins, e.g., homogeneous or heterogeneous formation of dimers and/or multimers. A combination of these two computational approaches will help us elucidate the transport mechanism of Hg(II) across the bacterial cytoplasmic membrane more clearly than is possible to obtain from experimental studies alone.

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