The agent responsible for the recent severe acute respiratory syndrome (SARS) outbreak is a previously unidentified coronavirus. While there is a wealth of epidemiological studies, little if any molecular characterization of SARS coronavirus (SCoV) proteins has been carried out. Here we describe the molecular characterization of SCoV E protein, a critical component of the virus responsible for virion envelope morphogenesis. We conclusively show that SCoV E protein contains an unusually short, palindromic transmembrane helical hairpin around a previously unidentified pseudo-center of symmetry, a structural feature which seems to be unique to SCoV. The hairpin deforms lipid bilayers by way of increasing their curvature, providing for the first time a molecular explanation of E protein's pivotal role in viral budding. The molecular understanding of this critical component of SCoV may represent the beginning of a concerted effort aimed at inhibiting its function, and consequently, viral infectivity.

We investigated the structure of the hydrophobic domain of the severe acute respiratory syndrome E protein in model lipid membranes by x-ray reflectivity and x-ray scattering. In particular, we used x-ray reflectivity to study the location of an iodine-labeled residue within the lipid bilayer. The label imposes spatial constraints on the protein topology. Experimental data taken as a function of protein/lipid ratio P/L and different swelling states support the hairpin conformation of severe acute respiratory syndrome E protein reported previously. Changes in the bilayer thickness and acyl-chain ordering are presented as a function of P/L, and discussed in view of different structural models.

Peptides with alternating amino acid configuration provide helical secondary structures that are especially known from the membrane channel and pore-forming gramicidin A. In analogy to this natural D,L-alternating pentadecapeptide, the potential of D,L-alternating peptides for membrane insertion is investigated using the model dodecamer peptide H-(Phe-Tyr)(5)-Trp-Trp-OH. This aromatic peptide is introduced as a novel pore-forming synthetic analogue of gramicidin A. It forms a well-organized homodimer similar to one of the gramicidin A transmembrane motifs. X-ray reflectivity measurements are performed on solid-supported peptide-lipid complexes to obtain information about the influence of the artificial dodecamer peptide on the bilayer parameters. In addition, Fourier-transform infrared (FTIR) and circular dichroism (CD) spectroscopic studies determine the conformational state of H-(Phe-Tyr)(5)-Trp-Trp-OH within the model membrane. Site-specific iodine labeling assists in determining the topology of the membrane-embedded peptide by pinpointing the position of the iodine label within the bilayers.

A technique for direct observation of particle motion under shear in a Langmuir monolayerThe ratio of the rotational and translational drag coefficient of a circular liquid condensed Langmuir monolayer domain moved in different phases is measured. A single domain is fixed at its boundary and forced to undergo combined translational and rotational motion. It is observed, that the drag force is dominated by the viscous dissipation of the three dimensional subphase and affected by the elasticity of the surrounding monolayer phase.

A Langmuir monolayer of methyl octadecanoate in the phase coexistence region liquid expanded/liquid condensed is observed with fluorescence microscopy and mechanically manipulated using optical tweezers. A circular liquid condensed droplet is locally fixed with the tweezers and deformed by hydrodynamic flow of the surroundings. The stationary shape is determined by the competition of the bare line tension λ, dipole and hydrodynamic forces. The dipole contributions to the shape can be accounted for by introducing an effective line tension λeff. At the front of the droplet a wedge angle θ is formed, from which λeff can be deduced. The electrostatic contribution λeff-λ is calculated for the experimental shape in the limit of weak deformations. The range of deformation where this approach holds is determined for a triangular shape.