The saposins are small, membrane-active proteins that exist in both soluble and lipid-bound states. Saposin A has roles in sphingolipid catabolism and transport and is required for the breakdown of galactosylceramide by β-galactosylceramidase. In the absence of lipid, saposin A adopts a closed monomeric apo conformation typical of this family. To study a lipid-bound state of this protein, we determined the crystal structure of saposin A in the presence of detergent to 1.9 Å resolution. The structure reveals two chains of saposin A in an open conformation encapsulating 40 internally bound detergent molecules organized in a highly ordered bilayerlike hydrophobic core. The complex provides a high-resolution view of a discoidal lipoprotein particle in which all of the internalized acyl chains are resolved. Saposin A lipoprotein discs exhibit limited selectivity with respect to the incorporated lipid, and can solubilize phospholipids, sphingolipids, and cholesterol into discrete, monodisperse particles with mass of approximately 27 kDa. These discs may be the smallest possible lipoprotein structures that are stabilized by lipid self-assembly.protein-lipid complex | X-ray crystallography | molecular dynamics | Krabbe disease

Saposin D is a sphingolipid activator protein required for the lysosomal breakdown of ceramide to a fatty acid and sphingosine by acid ceramidase. The crystal structure of saposin D has been determined in two different crystal forms, resulting in a total of six crystallographically independent views of this small 80-amino-acid protein. All of the structures are highly similar and reveal the monomeric form of the saposin fold previously seen in the crystal structures of saposins A and C. Saposin D is slightly more compact than the related saposins A and C owing to a slight repositioning of the 'stem' and 'hairpin' regions of the protein.

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MScases causes problems during complementary SEM/EDS analyses when the sample is not transferred onto a different sample holder with regard to minimization of risk of its damage, loss or contamination. Therefore monocrystalline silicon plates with indicated conductivity of 5 Ω.cm -1 were tested in practice. This value is sufficient for SEM (based on measurements -carbon conductive strips specially intended for SEM have the conductivity of approx. 500 kΩ and higher). The plates with thickness of 300µm (±15µm) can also be used for subsequent direct FTIR analysis even in transmission mode, without the need of plate exchange. A method employing the image analysis system was introduced for precise sample adjustment for microdiffraction and the choice of the area to be measured. The trace of the primary beam on a fluorescent disc was scanned for different angles 2theta and subsequently saved as binary overlay images. A camera reads the live image of the sample through the focusing microscope and the operator can choose a spot for the analysis in ergonomic conditions (the second monitor was placed directly into the diffractometer chamber). This procedure is very convenient for heterogeneous samples, various abrasions, etc.The system is further used for quantitative drug analysis. Both Rietveld method or method with the scale factor and the RIR (Reference Intensity Ratio) values (also called I/Ic values) are used. The results are cross-checked by standard methods of organic analysis (GCMS, FTIR), XRD analysis, in addition, enables precise phase analysis of inorganic components.

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