Poster presentation

1. Results (cont.)Results
Probing the active site of atypical butyrylcholinesterase with V-agents and V-agent analogs
Anastasia Neuman
Mentored by Dr. Tamara Otto
Graph 1: Spontaneous reactivation of aBuChE inhibited with OP nerve agents
VX and VR. Uninhibited aBuChE is shown (control; closed circles). Standard
error bars are shown.
Graph 2: Spontaneous reactivation of inhibited aBuChE with analogs V1, V2,
V3, V4, and V5. Uninhibited aBuChE is shown (control; closed circles).
Standard error bars are shown.
Figure 2: Molecular modeling of VR-inhibited aBuChE. A. P(+) isomer. B. P(-) isomer.
Protein backbone is shown in gray. Tyrosine 334 and water molecules are also depicted.
Dashed line between uppermost water molecule and gold phosphorus in B. shows a distance
of 5.91 angstroms.
Conclusions
The purpose of this project was to gain understanding of the
spontaneous reactivation of aBuChE. The aBuChE was inhibited with
nerve agents VX and VR. Surprisingly, VR-inhibited aBuChE was able to
undergo spontaneous reactivation (Graph 1). This reactivation was also
observed when aBuChE was inhibited by V3; however little to no
reactivation was detected with analogs V1, V2, V4, and V5 (Graph 2 and
Figure 1). The individual VR and V3 stereoisomers were examined for
the ability to inhibit the enzyme (Table 1). In each case, both
stereoisomers showed signs of reactivation but the P(+) isomer
reactivated more quickly than the P(-) isomer. Three-dimensional
molecular modeling studies revealed a network of water molecules within
three angstroms of the phosphorus atom in the P(+) VR isomer that was
not observed in the P(-) VR isomer modeling (Figure 2). These
molecules may play a part in reactivation. The residue tyrosine 334 (Tyr
334) undergoes a large movement between the models of the two
isomers and may be responsible for maintaining this network of water
molecules. Tyr 334 may be of interest for site-directed mutagenesis
studies to elucidate the mechanism of reactivation.
References
Mumford, H., Docx, C. J., Price, M. E., Green, A. C., Tatterstall, J. E., & Armstrong S. J.,
(2012). Human plasma-derived BuChE as a stoichiometric bioscavenger for treatment of
nerve agent poisoning. Chemico-Biological Interactions 203(1). doi: 10.1016/j.cbi.2012.08.018
Pezzementi, L., Nachon, F., & Chatonnet, A. (2011) Evolution of Acetylcholinesterase and
Butyrylcholinesterase in the Vertebrates: An Atypical Butyrylcholinesterase from the
Medaka Oryzias latipes. PLoS ONE 6(2): e17396.doi:10.1371/journal.pone.0017396
Acknowledgements
I would like to thank Dr. Tamara Otto, Rich Sweeney, Mrs. Linda McDonough, and the
Bioscavenger group at MRICD.
Introduction
When organophosphorus (OP) nerve agents enter the bloodstream,
they covalently bind to the active site serine of acetylcholinesterase
(AChE) and inhibit the enzyme. This inhibition prevents AChE from
hydrolyzing the neurotransmitter acetylcholine, resulting in multi-organ
failure and death. Human butyrylcholinesterase (BuChE) has been
recognized as a stoichiometric bioscavenger because it can bind to nerve
agent, thereby preventing the agent from exiting the bloodstream and
inhibiting AChE (Mumford et al., 2011). Atypical BuChE (aBuChE)
from the medaka Oryzias latipes is an intermediate form between AChE
and BuChE (Pezzementi, Nachon, & Chatonnet, 2011). This enzyme has
the potential to become a plausible bioscavenger if it can bind to nerve
agents. After analysis of aBuChE with a panel of nerve agents, it was
discovered that aBuChE spontaneously reactivates after inhibition with
the nerve agent VR and analog V3. The purpose of this project was to
probe the active site of aBuChE using a panel of five V-agent analogs to
better understand the mechanism(s) responsible for reactivations.
Elucidation of the mechanism responsible for reactivation may increase
the potential of aBuChE as a bioscavenger.
Analog t1/2 (hours)
VR Racemic 6.5 ± 0.07
VR P(+) 5.7 ± 0.2
VR P(-) 10.2 ± 1.4
V3 Racemic 5.5 ± 0.2
V3 P(+) 2.5 ± 0.04
V3 P(-) 4.0 ± 0.4
A. B.
Materials and Methods
VX N
S
P
O
O
V1 O
P
O
S
N
V2 O
P
O
S
N
V5 O
P
O
S
N
V4 O
P
O
S
N
VR
O
P
O
S
N
V3
O
P
O
S
N
Spontaneous Reactivation of Agent-Inhibited aBuChE
Spontaneous Reactivation of Analog-Inhibited aBuChE
Control
VR Racemic
VX Racemic
0 500 1000 1500
Time (min)
125
100
75
50
25
0
%Reactivation
0 500 1000 1500
Time (min)
125
100
75
50
25
0
%Reactivation
Control
V1 Racemic
V2 Racemic
V3 Racemic
V4 Racemic
V5 Racemic
Figure 1: Chemical structures of VX, VR, and V-
agent analogs.
Table 1: Half-time reactivation
rates (t1/2) of aBuChE.
Expression of aBuChE
The cDNA encoding aBuChE as well as an empty vector, pcDNA3.1
(control), were transfected into Human Embryonic Kidney 293T cells
using Lipofectamine™ 2000. Cells were incubated at 37 °C in a CO2
incubator for 48 hours. Cells were lysed in 100 mM KPO4, 1 M NaCl,
1% Triton X-100, pH 7.4 for 5 min at room temperature. Extracts were
centrifuged at 20,000g for 20 min, and the supernatants were stored at
-20 °C.
Reactivation of aBuChE
For nerve agent inhibition and reactivation studies, 1 µL nerve agent
was added to 50 µL whole cell lysate and incubated for 10 min at room
temperature. After incubation, samples were passed over a gel-filtration
column to remove unbound nerve agent. Twenty µL of the sample was
diluted in 1480 µL KPO4, pH 7.4 in a 96 well-plate and placed in the
Biomek Robot for monitoring. Samples were mixed with substrate
containing 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and
propionylthiocholine (PtCh) and the rate of hydrolysis of PtCh was
monitored at A412 in a spectrophotometer. Readings were taken every 30
minutes for 3 hours followed by every 4 hours for 20 hours.