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Disulfide Bond and Topological Isomerization of the Conopeptide PNID: Disulfide Bonds with a Twist.

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Title:Disulfide Bond and Topological Isomerization of the Conopeptide PNID: Disulfide Bonds with a Twist.
Authors:Espiritu, Michael J.
Contributors:Molecular Biosciences & Bioeng (department)
Keywords:Peptides
Conotoxins
Isomers
Topology
Nuclear Magnetic Resonance
Date Issued:May 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:Despite decades of research, efficient and accurate peptide and protein folding remains to be a
problematic feat. This is largely due to difficulty in determining ubiquitous folding
characteristics among diverse peptide sequences and in establishing an overarching theme in the
folding process. Thus it is critical to the advancement of knowledge on the topic that novel
sequences and frameworks of peptides continue to be studied. Conotoxins have proven to be
excellent subjects of study as they are small, bioactive, and their activity is often highly
dependent on achieving an appropriate fold. 􀁆/􀁏-Conotoxins have garnered significant interest
due to their selective and inhibitory properties at the norepinephrine transporter (NET) (1,2).
Here we present a novel 􀁆/􀁏-conotoxin, PnID, which unlike the previously reported members of
this class, is expressed as two native disulfide isomers within the venom duct extract of Conus
pennaceus. Additionally, synthetic production of this peptide resulted in one ribbon isomer and
two distinct topological globular isomers (named PnID Isomer B and PnID Isomer RevB), in
which their formation was later found to be individually controlled by the sequential order in
which their two disulfide bonds were selectively formed. Only one of the globular isomers, PnID
B, demonstrated a small amount activity at the monoamine transporters. The ribbon isomer,
PnID A showed inhibition of the NET, with and IC50 of 10 μM. A second globular isomer (with
reversed topology) PnID RevB, was separately produced and demonstrated no comparative
inhibition. NMR analysis and structure calculations revealed that the occurrence of these novel
topological isomers maybe due to a difference in two properties: (1) disulfide bond orientation,
with retention of same connectivity and (2) backbone flexibility. A critical turn between residues
5-8 within PnID appears to be largely affected by disulfide bond formation, where the more
active topology, PnID Isomer B possesses an increased chance of forming a 􀁊-turn, similar to the
turn seen in 􀁆-conotoxin MrIA, whereas the inactive isomer, PnID Isomer RevB, appears to have
a higher tendency to form an α-turn. The implication that disulfide bond connectivity alone may
not be enough information for the efficient synthetic reproduction of all Conus derived toxins is
novel and wide impacting; this then requires closer scrutiny to the physical orientation of
disulfide bonds in respect to each other. These findings implicate how pharmacological
selectivity and/or specificity may be influenced by the synthetic strategy in sequential selective
disulfide bond formation. We believe these findings could have implications on the future of
synthetically produced and rationally designed peptide drugs to enhance receptor-targeting
selectivity and/or specificity.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017.
URI/DOI:http://hdl.handle.net/10125/62553
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Molecular Biosciences and Bioengineering


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