Structure of Immune Stimulating Complex Matrices and Immune Stimulating Complexes in Suspension Determined by Small-Angle X-Ray Scattering

Abstract

Immune stimulating complex (ISCOM) particles consisting of a mixture of Quil-A, cholesterol, and phospholipids were structurally characterized by small-angle x-ray scattering (SAXS). The ISCOM particles are perforated vesicles of very well-defined structures. We developed and implemented a novel (to our knowledge) modeling method based on Monte Carlo simulation integrations to describe the SAXS data. This approach is similar to the traditional modeling of SAXS data, in which a structure is assumed, the scattering intensity is calculated, and structural parameters are optimized by weighted least-squares methods when the model scattering intensity is fitted to the experimental data. SAXS data from plain ISCOM matrix particles in aqueous suspension, as well as those from complete ISCOMs (i.e., with an antigen (tetanus toxoid) incorporated) can be modeled as a polydisperse distribution of perforated bilayer vesicles with icosahedral, football, or tennis ball structures. The dominating structure is the tennis ball structure, with an outer diameter of 40 nm and with 20 holes 5-6 nm in diameter. The lipid bilayer membrane is 4.6 nm thick, with a low-electron-density, 2.0-nm-thick hydrocarbon core. Surprisingly, in the ISCOMs, the tetanus toxoid is located just below the membrane inside the particles.

Calculation of Small-Angle Scattering Patterns

“…If the subunits in the model are randomly distributed, the intensity calculation can be again optimized, dividing the histogram into blocks. So, the computational time cost decreases to O[n/num blocks ], where num blocks is the number of blocks [8,72,73].…”

“…The calculation of the scattering intensity was performed using the optimized Debye equation in a slightly different implementation in order to include different contrasts and demonstrate the potential use of this approach. In the figure of the original article is possible see that the histogram approach also permits an easy computation of affine polydispersities [8,73].…”

Saponin Interactions with Model Membrane Systems – Langmuir Monolayer Studies, Hemolysis and Formation of ISCOMs

“…Structure properties were investigated by TEM (transmission electron microscopy), a widely used method for elucidation of ISCOM structures, but also by cryo transmission electron microscopy and atomic force microscopy [128,129]. Other methods for structure elucidation have also been used, such as DLS, to obtain information about particle size and particle size distribution [128]. Özel et al [130] investigated structural details with TEM of stained and dried ISCOMs (l " Fig.…”

“…Generally, the addition of at least 30 % of a phosphoplipid such as phosphatidylcholine is a prerequisite for the formation of ISCOM matrices. Besides cryo-transmission electron micropgraphs of spherical cage-like structures with holes perforating the surface in the range of 40-60 nm, Pedersen et al [128] characterized ISCOM structures by small-angle X-ray scattering (SAXS) as a new method in this field (l " Fig. 17).…”

Propriedades ópticas não lineares de segunda e terceira ordem de coloides magnéticos

“…A intensidade medida foi modelada como o espalhamento de um conjunto de nanopartículas de forma e tamanho característico. Nesse caso, a intensidadeé dada por: [106,107]. Assim, os dados experimentais de intensidade de espalhamento para as amostras MZS e MZC na ausência de campo magnético são mostrados na Fig.…”