Basic Residues at Position 11 of α-Conotoxin LvIA Influence Subtype Selectivity between α3β2 and α3β4 Nicotinic Receptors via an Electrostatic Mechanism.

Understanding the determinants of α-conotoxin (α-CTX) selectivity for different nicotinic acetylcholine receptor (nAChR) subtypes is a prerequisite for the design of tool compounds to study nAChRs. However, selectivity optimization of these small, disulfide-rich peptides is difficult not only because of an absence of α-CTX/nAChR co-structures but also because it is challenging to predict how a mutation to an α-CTX will alter its potency and selectivity. As a prototypical system to investigate selectivity, we employed the α-CTX LvIA that is 25-fold selective for the α3β2 nAChR over the related α3β4 nAChR subtype, which is a target for nicotine addiction.

Synthesis and Biological Activity of Novel α-Conotoxins Derived from Endemic Polynesian Cone Snails.

α-Conotoxins are well-known probes for the characterization of the various subtypes of nicotinic acetylcholine receptors (nAChRs). Identifying new α-conotoxins with different pharmacological profiles can provide further insights into the physiological or pathological roles of the numerous nAChR isoforms found at the neuromuscular junction, the central and peripheral nervous systems, and other cells such as immune cells. This study focuses on the synthesis and characterization of two novel α-conotoxins obtained from two species endemic to the Marquesas Islands, namely and .

Direct Transformation of N-Protected α,β-Unsaturated γ-Amino Amides into γ-Lactams through a Base-Mediated Molecular Rearrangement.

Here, we are reporting a single-step transformation of -protected α,β-unsaturated γ-amino amides into 5,5-disubstituted γ-lactams through a base-mediated new molecular rearrangement. In contrast to the known N- to C(O) cyclization of saturated γ-amino acids into corresponding γ-lactams, the new rearrangement involves the cyclization between N-terminal C- to C-terminal amide N. The cyclization process was initiated by the migration of double bond from α,β → β,γ position.

Impact of substituent effects on the design of β-sheet mimetics and β-double helices from (E)-vinylogous γ-amino acid oligomers.

Here we report the design, single crystal conformations, impact of the substituents and structural differences of two structurally important motifs, β-sheets and β-double helices. Though β-sheets are common structural motifs in protein structures, β-double helices are not common in proteins and peptides. We found that both β-sheet mimetics and β-double helices can be constructed from the homooligomers of α,β-unsaturated γ-amino acids.

Design of Helical Peptide Foldamers through α,β → β,γ Double-Bond Migration.

The direct transformation of nonhelical α,γ-hybrid peptides composed of alternating α- and E-vinylogous amino acids into 12-helical structures through a base-mediated α,β → β,γ double-bond migration is reported. The conformations of double-bond-migrated new 12-helices were studied in single crystals and in solution. Instructively, the 12-helices reported here were found to be acid labile, and they completely break down into the corresponding amino acid derivatives upon treatment with acids.

Structural Dimorphism of Achiral α,γ-Hybrid Peptide Foldamers: Coexistence of 12- and 15/17-Helices.

Here, novel 12-helices in α,γ-hybrid peptides composed of achiral α-aminoisobutyric acid (Aib) and 4-aminoisocaproic acid (Aic, doubly homologated Aib) monomers in 1:1 alternation are reported. The 12-helices were indicated by solution and crystal structural analyses of tetra- and heptapeptides. Surprisingly, single crystals of the longer nonapeptide displayed two different helix types: the novel 12-helix and an unprecedented 15/17-helix.

Non-classical Helices with cis Carbon-Carbon Double Bonds in the Backbone: Structural Features of α,γ-Hybrid Peptide Foldamers.

The impact of geometrically constrained cis α,β-unsaturated γ-amino acids on the folding of α,γ-hybrid peptides was investigated. Structure analysis in single crystals and in solution revealed that the cis carbon-carbon double bonds can be accommodated into the 12-helix without deviation from the overall helical conformation. The helical structures are stabilized by 4→1 hydrogen bonding in a similar manner to the 12-helices of β-peptides and the 310 helices of α-peptides.