13C- and1H-NMR. Spectra ofortho-benzoquinones. On the assignment problem in13C spectra

Cysteine modifiers suggest an allosteric inhibitory site on the CAL PDZ domain

Protein-protein interactions have become attractive targets for both experimental and therapeutic interventions. The PSD-95/Dlg1/ZO-1 (PDZ) domain is found in a large family of eukaryotic scaffold proteins that plays important roles in intracellular trafficking and localization of many target proteins. Here, we seek inhibitors of the PDZ protein that facilitates post-endocytic degradation of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR): the CFTR-associated ligand (CAL). We develop and validate biochemical screens and identify methyl-3,4-dephostatin (MD) and its analog ethyl-3,4-dephostatin (ED) as CAL PDZ inhibitors. Depending on conditions, MD can bind either covalently or non-covalently. Crystallographic and NMR data confirm that MD attacks a pocket at a site distinct from the canonical peptide-binding groove, and suggests an allosteric connection between target residue Cys³¹⁹ and the conserved Leu²⁹¹ in the GLGI motif. MD and ED thus appear to represent the first examples of small-molecule allosteric regulation of PDZ:peptide affinity. Their mechanism of action may exploit the known conformational plasticity of the PDZ domains and suggests that allosteric modulation may represent a strategy for targeting of this family of protein-protein binding modules.

An antiproliferative bis-prenylated quinone from the New Zealand brown alga Perithalia capillaris

Bioactivity-directed isolation work on the endemic New Zealand brown alga Perithalia capillaris, seeking anti-inflammatory compounds, led to a new bis-prenylated quinone ( 4). This compound inhibited superoxide production by human neutrophils in vitro (IC 50 2.1 microM), but was more potent at inhibiting proliferation of HL60 cells (IC 50 0.34 microM). Two related bis-prenylated phenols were also isolated, one known ( 2) and one new ( 5), with weaker biological activities. This report extends the examples of bis-prenylated phenols as chemotaxonomic markers for brown algae of the order Sporochnales.

Study of the chemical structures of the photo-cross-linking products between Tyr and the 5-azido-2-nitrobenzoyl residue

Irradiation of N-(tyrosyl)-N'-(5-azido-2-nitrobenzoyl)-1,2-diaminoethane (I) initiates chemical reactions that lead to different products depending on the experimental conditions. All of these products are attributed to the reactions of triplet 4-nitrobenzoyl nitrene (4NBN). The reactions of triplet 4NBN with the tyrosyl residue result in the formation of two distinct products: compound II, which is unstable in aqueous solution, and the stable compound cyclo-[1-(4'-nitro-3'-benzoyl)-2-(aminotyrosyl)-N,N'-ethylenediami ne] (III). The formation of II is detected only in aerobic conditions. The unstable photoproduct II converts almost completely into compound III when its solution is concentrated. The photoproducts II and III have absorption spectra that are close to those of the photolabelled peptides. This finding is important for speculating about the chemical nature of the photomodification products of protein tyrosyl residues by the arylazide group.