Topooptical investigations and enzymatic digestions on tissue-isolated amyloid fibrils

The structures and applications of microbial chondroitin AC lyase

As an important glycosaminoglycan hydrolase, chondroitin lyases can hydrolyze chondroitin sulfate (CS) and release disaccharides and oligosaccharides. They are further divided into chondroitin AC, ABC, and B lyases according to their spatial structure and substrate specificity. Chondroitin AC lyase can hydrolyze chondroitin sulfate A (CS-A), chondroitin sulfate C (CS-C), and hyaluronic acid (HA), making it an essential biocatalyst for the preparation of low molecular weight chondroitin sulfate, analysis of the structure of the chondroitin sulfate, treatment of spinal cord injury, and purification of heparin. This paper provides an overview of reported chondroitin AC lyases, including their properties and the challenges faced in industrial applications. Up to now, although many attempts have been adopted to improve the enzyme properties, the most important factors are still the low activity and stability. The relations between the stability of the enzyme and the spatial structure were also summarized and discussed. Also perspectives for remodeling the enzymes with protein engineering are included.

Improving sensitivity of amyloid detection by Congo red stain by using polarizing microscope and avoiding pitfalls

Systemic amyloidosis is a devastating group of disorders for which there is no current cure. The treatment goal is to reduce the burden of amyloidogenic protein precursors. The treatment is only effective if applied early in the disease process before significant and irreversible end organ damage has taken place. Congo red is still the standard stain used in most histopathology laboratories to identify amyloid material in tissues. The identification of Congophilic amyloid material is challenging because of multiple interfering factors. Here we describe improved sensitivity of identifying Congophilic materials in histologic sections using a metallurgical polarized microscope specifically constructed for polarized microscopy. The microscope is equipped with strain-free optics, matching polarizers, dis-integrated compensators, and a circular mobile stage. Compared to a standard clinical microscope, this setup significantly improves sensitivity of identifying amyloid material in Congo red-stained slides. We also describe the deleterious effect of plastic coverslip which can interfere with the ability to examine the slides under polarized light. We present a series of 10 different patients who had cardiac, brain, and salivary gland biopsies that were either equivocal or deemed negative using a standard clinical microscope but were positive using the equipment described above. These samples were confirmed to be positive by other methods including electron microscopy. We conclude that use of the correct equipment is needed before ruling out amyloidosis in tissue sections.

Polarization optical-histochemical characterization and supramolecular structure of carbohydrate fibrils

Topo-optical staining reactions were used to investigate the structures of bacterial cellulose, insect chitosan and alginic acid from brown algae. Polysaccharide complexes, glycosaminoglycans and sulfate groups were presented and demonstrated selectively. Chitosan and alginic acid are structurally similar to glycosaminoglycans (GAGs), which are constituents of human amyloid fibrils. The staining sequences shown can be used as reliable methods for histochemistry with light and polarization microscopy. They will help to clarify the complex protein-polysaccharide structure of amyloid fibrils.

Confocal fluorescence detected linear dichroism imaging of isolated human amyloid fibrils. Role of supercoiling

Amyloids are highly organized insoluble protein aggregates that are associated with a large variety of degenerative diseases. In this work, we investigated the anisotropic architecture of isolated human amyloid samples stained with Congo Red. This was performed by fluorescence detected linear dichroism (FDLD) imaging in a laser scanning confocal microscope that was equipped with a differential polarization attachment using high frequency modulation of the polarization state of the laser beam and a demodulation circuit. Two- and three-dimensional FDLD images of amyloids provided information on the orientation of the electric transition dipoles of the intercalated Congo Red molecules with unprecedented precision and spatial resolution. We show that, in accordance with linear dichroism imaging (Jin et al. Proc Natl Acad Sci USA 100:15294, 2003), amyloids exhibit strong anisotropy with preferential orientation of the dye molecules along the fibrils; estimations on the orientation angle, of around 45°, are given using a model calculation which takes into account the helical organization of the filaments and fibrils. Our data also show that FDLD images display large inhomogeneities, high local values with alternating signs and, in some regions, well identifiable µm-sized periodicities. These features of the anisotropic architecture are accounted for by supercoiling of helically organized amyloid fibrils.

The relevance of the aldehyde bisulfite toluidine blue reaction and its variants in the submicroscopic carbohydrate research

Carbohydrates are chemical compounds that contain only oxygen, hydrogen and carbon. They are classified by their number of sugar units: monosaccharides (such as glucose and fructose), and disaccharides (such as sucrose and lactose) are simple carbohydrates; oligosaccharides and polysaccharides (such as starch, glycogen and cellulose) are complex carbohydrates. Carbohydrates play a crucial role in diverse biological systems [Hricovín M. Structural aspects of carbohydrates and the relation with their biological properties. Curr Med Chem 2004;11:2565-83]. According to Roseman [Sugars of the cell membrane. In: Weissmann G, Clairborn E, editors. Cell membranes. Biochemistry, Cell Biology, Pathology. New York: H. P. Publ. Co; 1975. p. 55-64], two classes of glycoproteins are described. Free glycoproteins are localised in the surface coat of the membranes and form a thick mobile layer, without any association to the membrane itself. Functionally, however, they are located in a close association with the membrane (e.g. in the duodenal mucosa). The other group consists of the membrane glycoproteins, which are integral to the membranes and are located in the outer layer. The oligosaccharide chains are bound to the N-terminal part of proteins, and are situated in the hydrophilic zone. Glycoproteins have diverse functions. They are important in specific receptor functions, in immunological cell destruction and play a significant role in reactions with lectins, antibodies, as well as in cell association and mutual recognition of the cells. This paper focuses on aspects of a summary of polarisation optical investigations and biological functions of the following three groups of carbohydrates: oligosaccharides, glycoproteins and glycosaminoglycans.