1. Cyclization and Derivatization of the Potassium Channel Antagonist Tertiapin (TPNQ)
Vinay K. Menon* and Jon-Paul Bingham
Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, Honolulu, HI
• Fluorescent tagging of the bioengineered Cyclic TPNQ allows its absorption to be
traced through the body of the insect (i.e. GI absorption, systemic circulation and
binding at ROMK1 - later work)
• The fluorescent molecule (DyLight©) is conjugated to peptides via the Staudinger
reaction, that involves the phosphine group (R3P) of the fluorophore and an azide
group (N3) on the peptide chain
• This reaction results in a stable peptide bond between the fluorophore and the
peptide
• TPNQ is a stable derivative of a 21 amino acid peptide toxin extracted from
the European honey bee (Apis mellifera)
• Potent antagonist of the renal outer medullary potassium channel
(ROMK1) (Kd1.3nM)
• Other peptide inhibitors of ROMK1, like the scorpion toxin Lq2, has a Kd of
only 400nM
• ROMK1 Channel
• ATP-dependent inward rectifying potassium channel
• Insects: Found in an agricultural pest, the Fall Armyworm
(Spodoptera frugiperda)
• TPNQ’s high selectivity for ROMK1 and the presence of ROMK1 in S.
frugiperda make it a strong candidate for use as an insecticide
• Objective: Synthesize an orally stable form of TPNQ in order to enable
future use as an insecticide or therapeutic agent
ALCNCNRIIIPHQCWKKCGK-NH2
Figure 1. Sequence of TPNQ
Introduction
• Peptides are quickly degraded by enzymatic activity in the GI tract
destroying any potential therapeutic ability (Figure 2)
• Backbone cyclized peptides diminish the effect of degradative enzymes
enabling delivery of small molecules (i.e. drugs) to specific cells (Figure 3)
• Hypothesis: Cyclic TPNQ should show more resistance to digestive
enzymes than their linear counterparts
• http://www.cdc.gov/nchs/fastats/kidney-disease.htm
• http://www.cdc.gov/stroke/facts.htm
• http://www.aces.edu/pubs/docs/A/ANR-1019/ANR-1019.pdf
• http://ainfo.cnptia.embrapa.br/digital/bitstream/item/35507/1/Yield-
impact.pdf
References
The Benefit of Cyclic Peptides
+H3N R4R2 R3R1 COOHE E
R4
R2
R3
R1
E
ER4
R2
R3
R1
R4
R2
R3
R1
Figure 2. Enzymatic degradation of linear peptide
Figure 3. Enzymatic degradation of cyclic peptide
Fluorescent Tagging
Figure 4. Simplified schematic of fluorophore addition
H
N
R1
O
P
PhPh
O
OCH3
Lys-N3
H
N
R1
O
P
PhPh
O
H
N Lys
O *CLICK*
*CLICK*
Figure 5. Reaction mechanism of fluorophore addition via
the Staudinger reaction, also known as “click chemistry”
• In order to isolate the target peptide from impurities and side-products, crude
solutions are run through a reverse-phase high pressure liquid chromatography (RP-
HPLC) machine, which separates different molecules from each other based on how
they interact with a hydrophobic column
Figure 6. RP-HPLC chromatogram of pure linear reduced TPNQ
Results - Peptide Purification
• The mass of purified products are then confirmed using an
electrospray mass spectrometer (ES-MS)
• The dominant peaks in the spectra are compared to the
calculated mass of the target peptide
Results - Peptide Characterization
Figure 7. ES-MS spectra of TPNQ
Peptide Peptide Fluorophore
*CLICK*
*CLICK*
Fluorophore
Charge States Expected Mass (Da) Observed Mass (Da)
+0 (Parent Mass) 3080.5 Not observed
+1 3081.5 Not observed
+2 1541.25 Not observed
+3 1027.8 Not observed
+4 771.125 772.2
+5 617.1 618.1
+4 Charge State
+5 Charge State
RT = 38.084 min
S
SS
S
H2NCOOH
N
H
O
Analysis
Cyclization
Oxidation
Linear Reduced
Peptide
Cyclic Reduced
Peptide
Cyclic Oxidized
Peptide
• Fall Armyworm infestations cause $300-500 million in damage annually to
corn, alfalfa, soybean, cotton, and most vegetable crops
• Other synthetic insecticides are made from harsh chemicals that destroy crops
and beneficial insects and pollute the soil
• Since to bioengineered Cyclic TPNQ is a peptide composed of naturally
occurring amino acids, it would specifically target and kill the pest and then
breakdown into recyclable amino acids
Impact
A280
-0.05
0.00
0.05
0.10
Minutes
30.00 35.00 40.00 45.00 50.00
Column: Phenomenex C18
Size: 1 x 250 mm
Mobile phase:
A=0.1% TFA
B=90% MeCN, 0.08% TFA
Flow: 0.1 mL/min
Detection: UV 280 nm
% Solvent A
% Solvent B
Bioengineered Cyclic TPNQ
Fall Armyworm
(Spodoptera frugiperda)
Apis mellifera