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