Biological tissue exhibits an absorbance minimum in the near-infrared between 700 and 900 nm that permits deep penetration of light. Molecules that undergo photoisomerization in this bio-optical window are highly desirable as core structures for the development of photopharmaceuticals and as components of chemical-biological tools. We report the systematic design, synthesis, and testing of an azobenzene derivative tailored to undergo single-photon photoswitching with near-infrared light under physiological conditions. A fused dioxane ring and a methoxy substituent were used to place oxygen atoms in all four ortho positions, as well as two meta positions, relative to the azobenzene N═N double bond. This substitution pattern, together with a para pyrrolidine group, raises the pK of the molecule so that it is protonated at physiological pH and absorbs at wavelengths >700 nm. This azobenzene derivative, termed DOM-azo, is stable for months in neutral aqueous solutions, undergoes trans-to-cis photoswitching with 720 nm light, and thermally reverts to the stable trans isomer with a half-life near 1 s.

T20 (generic name: Enfuvirtide, brand name: Fuzeon) is the only FDA-approved HIV fusion inhibitor that is being used for treatment of HIV/AIDS patients who have failed to respond to current antiretroviral drugs. However, it rapidly induces drug resistance in vitro and in vivo. On the basis of the structural and functional information of anti-HIV peptides from a previous study, we designed an HIV fusion inhibitor named CP32M, a 32-mer synthetic peptide that is highly effective in inhibiting infection by a wide range of primary HIV-1 isolates from multiple genotypes with R5-or dual-tropic (R5X4) phenotype, including a group O virus (BCF02) that is resistant to T20 and C34 (another anti-HIV peptide). Strikingly, CP32M is exceptionally potent (at low picomolar level) against infection by a panel of HIV-1 mutants highly resistant to T20 and C34. These findings suggest that CP32M can be further developed as an antiviral therapeutic against multidrug resistant HIV-1.drug-resistance ͉ gp41 ͉ peptide ͉ six-helix bundle

Human immunodeficiency virus type 1 (HIV-1) entry into the host cell involves a cascade of events and currently represents one of most attractive targets in the search for new antiviral drugs. The fusion-active gp41 core structure is a stable six-helix bundle (6-HB) folded by its trimeric N-terminal heptad repeat (NHR) and C-terminal heptad repeat (CHR). Peptides derived from the CHR region of HIV-1 gp41 are potent fusion inhibitors that target the NHR to block viral and cellular membrane fusion in a dominant negative fashion. However, all CHR peptides reported to date are derived primarily from residues 628 to 673 of gp41; little attention has been paid to the upstream sequence of the pocket binding domain (PBD) in the CHR. Here, we have identified a motif ( 621 QIWNNMT 627 ) located at the upstream region of the gp41 CHR, immediately adjacent to the PBD ( 628 WMEWEREI 635 ). Biophysical characterization demonstrated that this motif is critical for the stabilization of the gp41 6-HB core. The peptide CP621-652, containing the 621 QIWNNMT 627 motif, was able to interact with T21, a counterpart peptide derived from the NHR, to form a typical 6-HB structure with a high thermostability (thermal unfolding transition [T m ] value of 82°C). In contrast, the 6-HB formed by the peptides N36 and C34, which has been considered to be a core structure of the fusion-active gp41, had a T m of 64°C. Different from T-20 (brand name Fuseon), which is the first and only HIV-1 fusion inhibitor approved for clinical use, CP621-652 could efficiently block 6-HB formation in a dose-dependent manner. Significantly, CP621-652 had potent inhibitory activity against HIV-1-mediated cell-cell fusion and infection, especially against T-20-and C34-resistant virus. Therefore, our works provide important information for understanding the core structure of the fusion-active gp41 and for designing novel anti-HIV peptides.The entry of human immunodeficiency virus type 1 (HIV-1) into target cells is mediated by the attachment of its envelope (Env) glycoprotein to cell surface receptors. The Env glycoprotein, a type I transmembrane protein, is originally synthesized as a single, glycosylated, polyprotein precursor, gp160, which is believed to assemble a trimeric structure in the endoplasmic reticulum and is subsequently cleaved by a cellular protease to yield a surface subunit, gp120, and a transmembrane subunit, gp41 (23, 53). gp120 is responsible for virus binding to its cell receptor, CD4, and a coreceptor (CRR5 or CXCR4). gp41 mediates membrane fusion of the virus with the target cell (45). Like other type I transmembrane proteins, the gp41 molecule consists of extracellular, transmembrane, and cytoplasmic domains (Fig. 1A). Its extracellular domain (ectodomain) contains four major functional regions: a hydrophobic, glycine-rich fusion peptide (FP), an N-terminal heptad repeat (NHR) (or HR1), a C-terminal heptad repeat (CHR) (or HR2), and a tryptophan-rich region. Both the NHR and CHR contain 4-3 repeats of hydrophobic amino acids predicted to f...

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Short peptides that have the ability to form stable alpha-helices in solution are rare, and a number of strategies have been used to produce them, including the use of metal chelation to stabilize folding of the backbone. However, no example exists of a structurally well-defined helix stabilized exclusively through metal ion chelation. Conantokins (con)-G and -T are short peptides that are potent antagonists of N-methyl-D-aspartate receptor channels. While con-G exhibits no helicity alone, it undergoes a structural transition to a helical conformation in the presence of a variety of multivalent cations, especially Mg2+ and Ca2+. This complexation also results in antiparallel dimerization of two peptide helices in the presence of Ca2+, but not Mg2+. A con-T variant, con-T[K7gamma], displays very similar behavior. We have solved the crystal structures of both Ca2+/con-G and Ca2+/con-T [K7gamma] at atomic resolution. These structures clearly show the nature of the metal-dependent dimerization and helix formation and surprisingly also show that the con-G dimer interface is completely different from the con-T[K7gamma] interface, even though the metal chelation is similar in the two peptides. This represents a new paradigm in helix stabilization completely independent of the hydrophobic effect, which we define as the "metallo-zipper."