The carbohydrate composition of human serum amyloid P component

Evolution of a supergene that regulates a trans-species social polymorphism

Supergenes are clusters of linked genetic loci that jointly affect the expression of complex phenotypes, such as social organization. Little is known about the origin and evolution of these intriguing genomic elements. Here we analyse whole-genome sequences of males from native populations of six fire ant species and show that variation in social organization is under the control of a novel supergene haplotype (termed Sb), which evolved by sequential incorporation of three inversions spanning half of a 'social chromosome'. Two of the inversions interrupt protein-coding genes, resulting in the increased expression of one gene and modest truncation in the primary protein structure of another. All six socially polymorphic species studied harbour the same three inversions, with the single origin of the supergene in their common ancestor inferred by phylogenomic analyses to have occurred half a million years ago. The persistence of Sb along with the ancestral SB haplotype through multiple speciation events provides a striking example of a functionally important trans-species social polymorphism presumably maintained by balancing selection. We found that while recombination between the Sb and SB haplotypes is severely restricted in all species, a low level of gene flux between the haplotypes has occurred following the appearance of the inversions, potentially mitigating the evolutionary degeneration expected at genomic regions that cannot freely recombine. These results provide a detailed picture of the structural genomic innovations involved in the formation of a supergene controlling a complex social phenotype.

Topo-optical reactions for the identification of O-acyl sugars in amyloid deposits

The aldehyde bisulfite toluidine blue (ABT) reaction with former saponification (KOH-ABT) and periodic acid-borohydride reduction-saponification (PB-KOH-ABT) were applied to sections of human amyloid deposits in the respiratory tract. The saponification-induced increase in ABT-reactivity was confined to the presence of O-acyl sugars associated with the amyloid fibrils. The anisotropic and metachromatic effect in the ABT and KOH-ABT reaction was reduced in the corresponding PB-KOH-ABT reaction, a difference attributed to the removal of staining due to neutral carbohydrate residues. Since the periodic acid-borohydride reduction abolishes all pre-existing ABT-reactivity of neutral sugar vicinal diols, the isolated KOH-effect could be shown using the PB-KOH-ABT reaction. By application of this sequence, the problem identifying small quantities of O-acyl sugars was solved. It is suggested that the KOH-effect depends upon the removal of O-acyl substituents located on the polyhydroxy side chain (C7, C8, C9) of sialic acid residues. An advantage of such topo-optical reactions over biochemical techniques is the exact localization of O-acyl sugars in tissue sites. By means of the KOH-ABT and PB-KOH-ABT reactions we have demonstrated, for the first time, that O-acyl sugars occur within amyloid deposits.

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.

Topo-optical visualization reactions of carbohydrate-containing amyloid deposits in the respiratory tract

Staining with Congo red according to is the most commonly used method for the demonstration of amyloid, but structures other than amyloid can give false-positive results. To overcome this problem, introduced an aqueous Congo red staining with gum arabic as the mounting medium, which we have used in this and previous publications. Most histochemical studies on amyloid deposits to date have concentrated on conventional methods including staining with thioflavine, sirius red, alcian blue, methyl and crystal violet. In this study, we used topo-optical reactions with thiazine dyes on both the light and polarization microscopic level to establish the structure, distribution and location of carbohydrate components that occur within amyloid deposits, especially in the respiratory tract. Topo-optical staining reactions for the qualitative analysis of carbohydrate components in amyloid deposits included (1) reactions that identify the carbohydrate residues, (2) reactions that detect sialic acids and, (3) methods that visualize glycosaminoglycans. In conclusion, a comparison of consecutive serial sections stained with Congo red, aldehyde bisulfite toluidine blue reaction, sialic acid-specific topo-optical reaction, toluidine blue topo-optical reaction and chemically intensified basophilic reaction showed correlative staining patterns and anisotropic effects, corresponding to a close pathomorphological relationship between amyloid fibrils, periodate reactive carbohydrates, including sialic acids, and glycosaminoglycans.

Human serum amyloid P component is an invariant constituent of amyloid deposits and has a uniquely homogeneous glycostructure

Human serum amyloid P component (SAP) is a normal plasma protein and the precursor of amyloid P component (AP), a universal constituent of the abnormal tissue deposits in amyloidosis, including Alzheimer disease. We show here that its single N-linked biantennary oligosaccharide does not display the microheterogeneity usually characteristic of glycoproteins. The protein and the glycan structures of AP were also invariant, their resistance to degradation suggesting a role in persistence of amyloid deposits. Asialo-SAP was rapidly cleared from the circulation in mice by a mechanism dependent on terminal galactose residues and was catabolized in hepatocytes. However blockade of this pathway did not affect the clearance of native SAP. Rapid hepatic uptake and catabolism of human asialo-SAP in man were also directly demonstrated. The protein and glycan homogeneity of SAP and the integrity of AP suggest that the complete glycoprotein structure is important for the normal and the pathophysiological functions of this molecule.

Human serum amyloid P-component (SAP) selectively binds to immobilized or bound forms of C-reactive protein (CRP)

The two homologous human pentraxins, C-reactive protein (CRP) and serum amyloid P-component (SAP), specifically bind to each other only when the CRP is in an immobilized form bound to one of its ligands or to an antibody. CRP did not bind to immobilized SAP. The binding of SAP to immobilized forms of CRP was Ca(2+)-dependent and of sufficient affinity to occur in the presence of serum or purified serum proteins. SAP bound preferentially to a synthetic peptide corresponding to the Ca(2+)-binding region of CRP. Monoclonal antibodies to a synthetic peptide corresponding to the Ca(2+)-binding region selectively inhibited the binding interaction. Proteolytic cleavage of CRP between residues 146 and 147 within the Ca2+ binding region abolished the SAP-binding site; however, the intact subunits of the pentameric CRP were capable of binding SAP. The significance of the binding interaction is that it may serve as the basis for localization of SAP to sites of tissue damage or repair, sites where CRP is selectively deposited.

Characterization of a calsequestrin-like protein from sea-urchin eggs

Following our studies on the identification of a calsequestrin-like protein (CSLP) from sea-urchin eggs [Oberdorf, Lebeche, Head & Kaminer (1988) J. Biol Chem. 263, 6806-6809], we have characterized its Ca(2+)-binding properties and identified it as a glycoprotein. The molecule binds 23 mol of Ca2+/mol of protein, as determined by equilibrium dialysis. This is in the range reported for cardiac calsequestrin but is about half the binding capacity of striated muscle calsequestrin. The affinities of the CSLP for Ca2+ are decreased by increasing KCl concentrations (20-250 mM) and the presence of Mg2+ (3 mM) in the medium: the half-maximal binding values varied from 1.62 to 5.77 mM. Hill coefficients indicated mild co-operativity in the Ca2+ binding. Ca2+ (1-8 mM)-induced u.v. difference spectra and intrinsic fluorescence changes suggest a net exposure of aromatic residues to an aqueous environment. C.d. measurements showed minor Ca(2+)-induced changes in alpha-helical and beta-sheet content of less than 10%. These spectral changes are distinctly different from those found in muscle calsequestrin. Immunoblotting studies showed that the CSLP is distinct from calreticulin, a low-affinity Ca(2+)-binding protein.

Structure and significance of N-linked sugar unit of human serum amyloid P component

Human serum amyloid P component (SAP) was digested with pronase P and a glycopeptide fraction was obtained by gel-permeation chromatography. Carbohydrate and amino-acid composition of the glycopeptide suggested that each subunit of SAP possesses an N-linked glycan, but no O-linked ones. The N-linked oligosaccharide of SAP was obtained by hydrazynolysis. The structure of the oligosaccharide, which was deduced by sequential digestion with exoglycosidases and subsequent gel filtration, was identical or very similar to that of human transferrin. Removal of sialic acids from SAP reduced the calcium-dependent binding activity for agarose by 7%, suggesting the terminal sialic acids were partially responsible for the binding.