Molecular Transport Through Blood-Brain Barrier Pores€¦ · Blood Brain Barrier Claudin-5 cis...
Transcript of Molecular Transport Through Blood-Brain Barrier Pores€¦ · Blood Brain Barrier Claudin-5 cis...
Molecular Transport through Blood-Brain Barrier PoresFlaviyan Jerome Irudayanathan and Shikha Nangia
Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse NY 13244, United States
Simulations were carried in the GPU nodes available at TACC STAMPEDE HPC cluster hosted and
supported by the Extreme Science and Engineering Discovery Environment (XSEDE). This research work
is funded by NSF CAREER CBET-1453312 and Syracuse University.
Acknowledgement1. Günzel, D. and A.S.L. Yu, 93, 525-569, (2013).
2. Krause, G., et al., Biomembranes, 1778, 631-645, (2008).
3. Piontek, J., et al., FASEB. 22, 146-158, (2008).
4. Suzuki, H., et al., Science, 344, 304-307, (2014).
5. Ohtsuki, S., et al., Journal of Cellular Physiology, 210,81-86, (2007).
6. Rossa, J., et al., Ann. New York Academy of Sciences, 1257, 59-66, (2012).
7. Rossa, J., et al., Journal of Biological Chemistry, 289(11), 7641-53, (2014).
8. Irudayanathan, F., et al., Journal of Physical Chemistry B, 120 (1), 77-88, (2016).
References
IntroductionThe brain is protected from harmful invasions by the molecular interface of
blood brain barrier (BBB). The BBB is critical in maintaining the homeostasis of
the central nervous system. Claudin-5 membrane proteins constitute tight
junctions (TJ) that act as gatekeepers of molecular transport in the BBB. These
tight junctions only allow ~2% of biologically relevant molecules to enter the
brain.(1-4) A vast majority of life saving drugs are denied access into the CNS.
This selective permeability is the largest hurdle in treating CNS diseases such
as Alzheimer's disease, Parkinson’s disease, and cancers originating in the
brain.(5-8)
Methods High accuracy homology modeling with crystal structure as
templates
Atomistic molecular dynamics with CHARMM36 force field
Coarse grained molecular dynamics for ~200 μs
Reverse transformation and characterization of dimer
interfaces
Molecular docking and characterization to elucidate the
pore structure
Atomistic monomer CG monomerClaudin-5 Monomer
Simulation Details
Claudin-5 Lipid Water Ions
The TJ assembly across two large membrane patches, which represent neighboring cells.
20 µs snapshot
System componentsSystem setup
Claudin Interactions
Small Molecules
Blood Brain Barrier
Claudin-5 cis assembly Four main dimeric interfaces were
observed in claudin-5 cis assembly
that matched with experimental
findings from independent labs (8).
Orientation analysis was used to
generate probability density of dimers
distributions in claudin-5. Single point mutation were performed,
similar to the experiments performed
by Rossa et al (7).
We identified that the population of
Dimer B is affected by this mutation,
hence we propose that Dimer B is
involved in forming TJ pores.
Using molecular docking approach we arrived at possible trans interaction interface
formed by the different dimers.
We discovered that both dimers B and D form pore like assembly when docked
Pore I formed by dimer D is 9.0±1.5 Å in diameter and is similar to the model
previously published (5)
Simulation snapshotsPore Structure Pore II Dynamics
Pro
ba
bility
de
ns
ity
Conclusions
ξ (nm)
PM
F k
ca
l/m
ol
Pore II based on Dimer B
Pore I based on Dimer D
Identified four different dimeric interfaces of which two form pores.
Characterized the pore structure and molecular transport through the pore.
From the PMF calculations it is evident that glucose experiences ~6.5
kcal/mol energy barrier to translocate through the claudin-5 pore II
Water on the other hand is able to translocate with no significant energy
barrier
Detailed characterization of the transport of other small molecules and ions
will help us unravel the molecular underpinnings of the claudin-5 pores
These findings are very significant in understanding the blood-brain barrier
tight junction and the nature of its molecular selectivity.
Pore II formed by dimer B has 9.5 ± 2.0 Å diameter.
The excluded volume of the Pore II is wide enough to allow small molecule
transport.
We further confirmed the existence of the trans interactions as observed in the
pore models using CG simulations
To demonstrate the transport characteristics of the pore we performed steered
molecular dynamics simulation of α-D-Glucose and water molecule through pore II.
Dimer conformations