Targeting Specific PDZ Domains of PSD-95 Structural Basis for Enhanced Affinity and Enzymatic Stability of a Cyclic Peptide

AbstractA cyclic peptide, Tyr-Lys-c[-Lys-Thr-Glu(βAla)-]-Val, incorporating a β-Ala lactam side chain linker and designed to target the PDZ domains of the postsynaptic density protein 95 (PSD-95), has been synthesized and structurally characterized by NMR while free and bound to the PDZ1 domain of PSD-95. While bound, the lactam linker of the peptide makes a number of unique contacts outside the canonical PDZ binding motif, providing a novel target for PDZ-domain specificity as well as producing a 10-fold enhancement in binding affinity. Additionally, the cyclization greatly enhances the enzymatic stability, increasing the duration that the peptide inhibits the association between PSD-95 and glutamate receptors, effectively inhibiting the clustering of kainate receptors for over 14 hr after application. Highly specific regulation of kainate receptor action may provide a novel route for treatment of drug addiction and epilepsy

Inhibition of N-Methyl-D-aspartate-induced Retinal Neuronal Death by Polyarginine Peptides Is Linked to the Attenuation of Stress-induced Hyperpolarization of the Inner Mitochondrial Membrane Potential

It is widely accepted that overactivation of NMDA receptors, resulting in calcium overload and consequent mitochondrial dysfunction in retinal ganglion neurons, plays a significant role in promoting neurodegenerative disorders such as glaucoma. Calcium has been shown to initiate a transient hyperpolarization of the mitochondrial membrane potential triggering a burst of reactive oxygen species leading to apoptosis. Strategies that enhance cell survival signaling pathways aimed at preventing this adverse hyperpolarization of the mitochondrial membrane potential may provide a novel therapeutic intervention in retinal disease. In the retina, brain-derived neurotrophic factor has been shown to be neuroprotective, and our group previously reported a PSD-95/PDZ-binding cyclic peptide (CN2097) that augments brain-derived neurotrophic factor-induced pro-survival signaling. Here, we examined the neuroprotective properties of CN2097 using an established retinal in vivo NMDA toxicity model. CN2097 completely attenuated NMDA-induced caspase 3-dependent and -independent cell death and PARP-1 activation pathways, blocked necrosis, and fully prevented the loss of long term ganglion cell viability. Although neuroprotection was partially dependent upon CN2097 binding to the PDZ domain of PSD-95, our results show that the polyarginine-rich transport moiety C-R(7), linked to the PDZ-PSD-95-binding cyclic peptide, was sufficient to mediate short and long term protection via a mitochondrial targeting mechanism. C-R(7) localized to mitochondria and was found to reduce mitochondrial respiration, mitochondrial membrane hyperpolarization, and the generation of reactive oxygen species, promoting survival of retinal neurons

Role of PLEXIND1/TGFβ signaling axis in pancreatic ductal adenocarcinoma progression correlates with the mutational status of KRAS

PLEXIND1 is upregulated in several cancers, including pancreatic ductal adenocarcinoma (PDAC). It is an established mediator of semaphorin signaling, and neuropilins are its known coreceptors. Herein, we report data to support the proposal that PLEXIND1 acts as a transforming growth factor beta (TGFβ) coreceptor, modulating cell growth through SMAD3 signaling. Our findings demonstrate that PLEXIND1 plays a pro-tumorigenic role in PDAC cells with oncogenic KRAS (KRASmut). We show in KRASmut PDAC cell lines (PANC-1, AsPC-1,4535) PLEXIND1 downregulation results in decreased cell viability (in vitro) and reduced tumor growth (in vivo). Conversely, PLEXIND1 acts as a tumor suppressor in the PDAC cell line (BxPC-3) with wild-type KRAS (KRASwt), as its reduced expression results in higher cell viability (in-vitro) and tumor growth (in vivo). Additionally, we demonstrate that PLEXIND1-mediated interactions can be selectively disrupted using a peptide based on its C-terminal sequence (a PDZ domain-binding motif), an outcome that may possess significant therapeutic implications. To our knowledge, this is the first report showing that (1) PLEXIND1 acts as a TGFβ coreceptor and mediates SMAD3 signaling, and (2) differential roles of PLEXIND1 in PDAC cell lines correlate with KRASmut and KRASwt status

Dual role of the exocyst in AMPA receptor targeting and insertion into the postsynaptic membrane

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102104/1/emboj7601065.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102104/2/emboj7601065-sup-0001.pd

Chemically modified peptide scaffolds target the CFTR-associated ligand PDZ domain.

PDZ domains are protein-protein interaction modules that coordinate multiple signaling and trafficking pathways in the cell and that include active therapeutic targets for diseases such as cancer, cystic fibrosis, and addiction. Our previous work characterized a PDZ interaction that restricts the apical membrane half-life of the cystic fibrosis transmembrane conductance regulator (CFTR). Using iterative cycles of peptide-array and solution-binding analysis, we targeted the PDZ domain of the CFTR-Associated Ligand (CAL), and showed that an engineered peptide inhibitor rescues cell-surface expression of the most common CFTR disease mutation ΔF508. Here, we present a series of scaffolds containing chemically modifiable side chains at all non-motif positions along the CAL PDZ domain binding cleft. Concordant equilibrium dissociation constants were determined in parallel by fluorescence polarization, isothermal titration calorimetry, and surface plasmon resonance techniques, confirming robust affinity for each scaffold and revealing an enthalpically driven mode of inhibitor binding. Structural studies demonstrate a conserved binding mode for each peptide, opening the possibility of combinatorial modification. Finally, we diversified one of our peptide scaffolds with halogenated substituents that yielded modest increases in binding affinity. Overall, this work validates our approach and provides a stereochemical foundation for further CAL inhibitor design and screening

The use of peptide as novel antibiotic development against the bacterial ribosome

International audienc

Electron density of chemically modified peptides.

<p>A) Prior to ligand modeling, positive electron density was observed in <i>F</i>_O – <i>F</i>_C difference maps, as illustrated here (contour level: 2σ) for the halogenated substituents attached to the Lys side chain at P⁻¹. B) After iterative rounds of refinement and model building, final 2<i>F</i>_O – <i>F</i>_C electron density maps (contour level: 1σ) showed excellent agreement with the model, as shown here for the corresponding P⁻¹ side chains. The final refined peptide structures are shown as stick figures and colored by atom/position (C = light blue for P⁻¹ or black for other positions, O = blue, F = sky blue, N = red, Br = dark red). The van der Waals surface of CALP is shown in gray. The substituents are indicated as follows: Tfa, trifluoroacetic acid; FB, 4-fluorobenzoic acid; BB, 4-bromobenzoic acid.</p

Differential stereochemical and electrostatic environments at each modifiable position.

<p>The electrostatic potential surface map of CALP is shown, rendered at ±10 k_BT/e (negative surface in red, positive surface in blue). Boxes and labels (S⁻¹, S⁻², etc.) indicate an approximate area that chemical modifications could bind when attached to the lysine N_ζ moiety at that position. Overlap in accessible area suggests a possible region for side-chain cyclization. Peptide backbones are shown as black C_α traces, with acetyl-lysine residues shown as sticks and colored by position. Non-carbon atoms are colored separately: O = blue, N = red.</p