Membrane topology of the colicin E1 channel using genetically encoded fluorescence.

The membrane topology of the colicin E1 channel domain was studied by fluorescence resonance energy transfer (FRET). The FRET involved a genetically encoded fluorescent amino acid (coumarin) as the donor and a selectively labeled cysteine residue tethered with DABMI (4-(dimethylamino)phenylazophenyl-4'-maleimide) as the FRET acceptor. The fluorescent coumarin residue was incorporated into the protein via an orthogonal tRNA/aminoacyl-tRNA synthetase pair that allowed selective incorporation into any site within the colicin channel domain. Each variant harbored a stop (TAG) mutation for coumarin incorporation and a cysteine (TGT) mutation for DABMI attachment. Six interhelical distances within helices 1-6 were determined using FRET analysis for both the soluble and membrane-bound states. The FRET data showed large changes in the interhelical distances among helices 3-6 upon membrane association providing new insight into the membrane-bound structure of the channel domain. In general, the coumarin-DABMI FRET interhelical efficiencies decreased upon membrane binding, building upon the umbrella model for the colicin channel. A tentative model for the closed state of the channel domain was developed based on current and previously published FRET data. The model suggests circular arrangement of helices 1-7 in a clockwise direction from the extracellular side and membrane interfacial association of helices 1, 6, 7, and 10 around the central transmembrane hairpin formed by helices 8 and 9.

A microwave-assisted synthesis of (S)-N-protected homoserine γ-lactones from L-aspartic acid.

A three-pot preparation of (S)-N-protected homoserine γ-lactones is presented. Conversion of N-protected L-aspartic acid to an oxazolidinone is followed by selective reduction/acid-catalyzed cyclization to deliver the lactones. Microwave irradiation proved valuable for improving the latter reaction steps in some cases.

Nucleophilic attack of 2-sulfinyl acrylates: a mild and general approach to sulfenic acid anions.

An increasing number of reactions of sulfenic acid anions are being demonstrated in the literature. As such, mild, general and reliable means for the generation of sulfenates are due. In the current paper, an addition/elimination of 2-sulfinyl acrylates using various nucleophiles is demonstrated and evaluated as a protocol for alkane- and arenesulfenate generation. Cyclohexanethiolate, methoxide and n-butyllithum each exhibit some merit for the reaction, and the thiolate is established as a mild, selective and effective reagent to release sulfenates from 2-sulfinyl acrylates. The stereospecificity of the addition/elimination of each nucleophile is recognized, and an explanation for the specificity is offered for thiolate and methoxide.

Diastereoselective alkylations of a protected cysteinesulfenate.

To further understand stereoselection in the alkylation of sulfenate anions, a protected cysteinesulfenate was generated in THF solution at low temperature. Introduction of a reactive alkylating agent brings about a cysteinyl sulfoxide in 51-75% yield, with diastereomeric ratios at the sulfinyl group ranging from 83:17 to 95:5. An internally complexed lithium counterion is proposed to account for the stereoselectivity.

Bis(2-bromo-benz-yl) tris-ulfide.

The title mol-ecule, C(14)H(12)Br(2)S(3), lies on a crystallographic twofold rotation axis which bis-ects the S-S-S angle. The dihedral angle between the two symmetry-related benzene rings is 89.91 (9)°. In terms of hybridization principles, the S-C-C angle is slightly larger than expected.

Monoclinic modification of N-[(1,1-dimethyl-ethoxy)carbon-yl]-3-[(R)-prop-2-en-1-ylsulfin-yl]-(R)-alanine ethyl ester at 200†(1) K.

In the monoclinic polymorph of the title compound, C(13)H(23)NO(5)S, inter-molecular N-H⋯O hydrogen bonds link mol-ecules into one-dimensional chains along [100]. The atoms of the terminal propenyl group are disordered over two sets of sites with refined occupancies of 0.69 (2) and 0.31 (2).

Triclinic modification of N-[(1,1-di-methyl-ethoxy)carbon-yl]-3-[(R)-prop-2-en-1-ylsulfin-yl]-(R)-alanine ethyl ester at 120†(1) K.

There are two independent mol-ecules in the asymmetric unit of the title compound, C(13)H(23)NO(5)S. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds link mol-ecules into two independent one-dimensional chains along [100]. The crystal studied was found to be a non-merohedral twin with a ratio of 0.615 (6):0.385 (1) for the refined components. At 200 (1) K [Singh et al. (2009 ▶). Acta Cryst. E65, o1385-o1386] the crystal structure of the title compound contains one disordered mol-ecule in the asymmetric unit of a monoclinic unit cell.

Synthesis and activity of a novel diether phosphonoglycerol in phospholipase-resistant synthetic lipid:peptide lung surfactants().

This paper reports the chemical synthesis and purification of a novel phospholipase-resistant C16:0, C16:1 diether phosphonoglycerol with structural analogy to ester-linked anionic phosphatidylglycerol (PG) in endogenous pulmonary surfactant. This diether phosphonoglycerol (PG 1) is studied for phospholipase A(2) (PLA(2)) resistance and for surface activity in synthetic exogenous surfactants combined with Super Mini-B (S-MB) peptide and DEPN-8, a previously-reported diether phosphonolipid analog of dipalmitoyl phosphatidylcholine (DPPC, the major zwitterionic phospholipid in native lung surfactant). Activity experiments measured both adsorption and dynamic surface tension lowering due to the known importance of these surface behaviors in lung surfactant function in vivo. Synthetic surfactants containing 9 : 1 DEPN-8:PG 1 + 3% S-MB were resistant to degradation by PLA(2) in chromatographic studies, while calf lung surfactant extract (CLSE, the substance of the bovine clinical surfactant Infasurf®) was significantly degraded by PLA(2). The 9 : 1 DEPN-8:PG 1 + 3% S-MB mixture also had small but consistent increases in both adsorption and dynamic surface tension lowering ability compared to DEPN-8 + 3% S-MB. Consistent with these surface activity increases, molecular dynamics simulations using Protein Modeller, GROMACS force-field, and PyMOL showed that bilayers containing DPPC and palmitoyl-oleoyl-PC (POPC) as surrogates of DEPN-8 and PG 1 were penetrated to a greater extent by S-MB peptide than bilayers of DPPC alone. These results suggest that PG 1 or related anionic phosphono-PG analogs may have functional utility in phospholipase-resistant synthetic surfactants targeting forms of acute pulmonary injury where endogenous surfactant becomes dysfunctional due to phospholipase activity in the innate inflammatory response.