Crystal structures of human immune protein FIBCD1 suggest an extended binding site compatible with recognition of pathogen-associated carbohydrate motifs.

Fibrinogen C domain-containing protein 1 (FIBCD1) is an immune protein proposed to be involved in host recognition of chitin on the surface of pathogens. As FIBCD1 readily binds acetylated molecules, we have determined the high-resolution crystal structures of a recombinant fragment of the FIBCD1 C-terminal domain complexed with small N-acetyl-containing ligands to determine the mode of recognition. All ligands bind at the conserved N-acetyl-binding site (S1) with galactose and glucose-derived ligands rotated 180° relative to each other.

Monomeric C-Reactive Protein in Serum With Markedly Elevated CRP Levels Shares Common Calcium-Dependent Ligand Binding Properties With an Dissociated Form of C-Reactive Protein.

A monomeric form of C-reactive protein (CRP) which precipitates with cell wall pneumococcal C polysaccharide (CWPS) and retains the ability to reversibly bind to its ligand phosphocholine has been produced through urea-induced dissociation at an optimized concentration of 3 M urea over a 10 weeks period. Dissociated samples were purified via size exclusion chromatography and characterized by western blot, phosphocholine affinity chromatography and CWPS precipitation. Human serum samples from patients with raised CRP levels (>100 mg/L as determined by the clinical laboratory assay) were purified by affinity and size exclusion chromatography and analyzed ( = 40) to determine whether circulating monomeric CRP could be detected .

Atomic-resolution crystal structures of the immune protein conglutinin from cow reveal specific interactions of its binding site with -acetylglucosamine.

Bovine conglutinin is an immune protein that is involved in host resistance to microbes and parasites and interacts with complement component iC3b, agglutinates erythrocytes, and neutralizes influenza A virus. Here, we determined the high-resolution (0.97-1.

Structural definition of hSP-D recognition of Salmonella enterica LPS inner core oligosaccharides reveals alternative binding modes for the same LPS.

The crystal structures of a biologically and therapeutically active recombinant homotrimeric fragment of native human SP-D (hSP-D) complexed with the inner core oligosaccharide of the Salmonella enterica sv Minnesota rough strains R5 and R7 (rough mutant chemotypes Rc and Rd1) have been determined. The structures reveal that hSP-D specifically and preferentially targets the LPS inner core via the innermost conserved Hep-Kdo pair with the flexibility for alternative recognition when this preferred epitope is not available for binding. Hep-Kdo binding is achieved through calcium dependent recognition of the heptose dihydroxyethyl side chain coupled with specific interactions between the Kdo and the binding site flanking residues Arg343 and Asp325 with evidence for an extended binding site for LPS inner cores containing multiple Kdo residues.

Crystal Structure of a Complex of Surfactant Protein D (SP-D) and Haemophilus influenzae Lipopolysaccharide Reveals Shielding of Core Structures in SP-D-Resistant Strains.

The carbohydrate recognition domains (CRDs) of lung collectin surfactant protein D (SP-D) recognize sugar patterns on the surface of lung pathogens and promote phagocytosis. Using Haemophilus influenzae Eagan strains expressing well-characterized lipopolysaccharide (LPS) surface structures of various levels of complexity, we show that bacterial recognition and binding by SP-D is inversely related to LPS chain extent and complexity. The crystal structure of a biologically active recombinant trimeric SP-D CRD complexed with a delipidated Eagan 4A LPS suggests that efficient LPS recognition by SP-D requires multiple binding interactions utilizing the three major ligand-binding determinants in the SP-D binding pocket, with Ca-dependent binding of inner-core heptose accompanied by interaction of anhydro-Kdo (4,7-anhydro-3-deoxy-d-manno-oct-2-ulosonic acid) with Arg343 and Asp325.

Feeding common carp Cyprinus carpio with β-glucan supplemented diet stimulates C-reactive protein and complement immune acute phase responses following PAMPs injection.

The effect of β-glucan as a feed additive on the serum and gene profile of C-reactive protein (CRP) and complement acute phase responses was ascertained in common carp Cyprinus carpio. In addition effects of subsequent intraperitoneal injections of pathogen-associated molecular patterns (PAMPs), i.e.

Crystal structure of the tetrameric fibrinogen-like recognition domain of fibrinogen C domain containing 1 (FIBCD1) protein.

The high resolution crystal structures of a recombinant fragment of the C-terminal fibrinogen-like recognition domain of FIBCD1, a vertebrate receptor that binds chitin, have been determined. The overall tetrameric structure shows similarity in structure and aggregation to the horseshoe crab innate immune protein tachylectin 5A. The high affinity ligand N-acetylmannosamine (ManNAc) binds in the S1 site, predominantly via the acetyl group with the oxygen and acetamide nitrogen hydrogen-bonded to the protein and the methyl group inserted into a hydrophobic pocket.

Serum amyloid P component accelerates the formation and enhances the stability of amyloid fibrils in a physiologically significant under-saturated solution of amyloid-β42.

The mechanism whereby an under-saturated solution of amyloid-β (Aβ)42 precipitates as β sheets in vivo in Alzheimer's disease remains to be elucidated. Herein we present in vitro evidence that serum amyloid P component may mediate this process through its acceleration of amyloid formation from an under-saturated solution of Aβ42 and subsequently its stabilization of the amyloid fibrils formed over physiologically significant timeframes. Our observations support serum amyloid P component as a therapeutic target in Alzheimer's disease.

Crystal structures of Limulus SAP-like pentraxin reveal two molecular aggregations.

The serum-amyloid-P-component-like pentraxin from Limulus polyphemus, a recently discovered pentraxin species and important effector protein of the hemolymph immune system, displays two distinct doubly stacked cyclic molecular aggregations, heptameric and octameric. The refined three-dimensional structures determined by X-ray crystallography, both based on the same cDNA sequence, show that each aggregate is constructed from a similar dimer of protomers, which is repeated to make up the ring structure. The native octameric form has been refined at a resolution of 3 A, the native heptameric form at 2.

Serum CRP-like protein profile in common carp Cyprinus carpio challenged with Aeromonas hydrophila and Escherichia coli lipopolysaccharide.

The potential of C-reactive protein (CRP)-like proteins to be used as a biomarker of health status in cultured carp obtained from various European fish lines has been assessed. Varying CRP-like protein levels in the serum of carp were monitored using an indirect competitive enzyme-linked immunosorbent assay. CRP-like protein basal levels in normal fish varied between carp lines, ranging on average from 2.

Surfactant proteins SP-A and SP-D: structure, function and receptors.

Surfactant proteins, SP-A and SP-D, are collagen-containing C-type (calcium dependent) lectins called collectins, which contribute significantly to surfactant homeostasis and pulmonary immunity. These highly versatile innate immune molecules are involved in a range of immune functions including viral neutralization, clearance of bacteria, fungi and apoptotic and necrotic cells, down regulation of allergic reaction and resolution of inflammation. Their basic structures include a triple-helical collagen region and a C-terminal homotrimeric lectin or carbohydrate recognition domain (CRD).

Structural and functional anatomy of the globular domain of complement protein C1q.

C1q is the first subcomponent of the classical pathway of the complement system and a major connecting link between innate and acquired immunity. As a versatile charge pattern recognition molecule, C1q is capable of engaging a broad range of ligands via its heterotrimeric globular domain (gC1q) which is composed of the C-terminal regions of its A (ghA), B (ghB) and C (ghC) chains. Recent studies using recombinant forms of ghA, ghB and ghC have suggested that the gC1q domain has a modular organization and each chain can have differential ligand specificity.

C1q and tumor necrosis factor superfamily: modularity and versatility.

C1q is the target recognition protein of the classical complement pathway and a major connecting link between innate and acquired immunity. As a charge pattern recognition molecule of innate immunity, C1q can engage a broad range of ligands via its globular (gC1q) domain and modulate immune cells, probably via its collagen region. The gC1q signature domain, also found in many non-complement proteins, has a compact jelly-roll beta-sandwich fold similar to that of the multifunctional tumor necrosis factor (TNF) ligand family.

The three-dimensional structure of calcium-depleted human C-reactive protein from perfectly twinned crystals.

C-reactive protein is a member of the pentraxin family of oligomeric serum proteins which has been conserved through evolution, homologues having been found in every species in which they have been sought. Human C-reactive protein (hCRP) is the classical acute-phase reactant produced in large amounts in response to tissue damage and inflammation and is used almost universally as a clinical indicator of infection and inflammation. The role of hCRP in host defence and the calcium-dependent ligand-binding specificity of hCRP for phosphocholine moieties have long been recognized.

Comparison of different crystal forms of 3-dehydroquinase from Salmonella typhi and its implication for the enzyme activity.

The type I 3-dehydroquinate dehydratase (DHQase) which catalyses the reversible dehydration of 3-dehydroquinic acid to 3-dehydroshikimic acid is involved in the shikimate pathway for the biosynthesis of aromatic compounds. The shikimate pathway is absent in mammals, which makes structural information about DHQase vital for the rational design of antimicrobial drugs and herbicides. The crystallographic structure of the type I DHQase from Salmonella typhi has now been determined for the native form at 1.

Complete cDNA sequence of SAP-like pentraxin from Limulus polyphemus: implications for pentraxin evolution.

The serum amyloid P component (SAP)-like pentraxin Limulus polyphemus SAP is a recently discovered, distinct pentraxin species, of known structure, which does not bind phosphocholine and whose N-terminal sequence has been shown to differ markedly from the highly conserved N terminus of all other known horseshoe crab pentraxins. The complete cDNA sequence of Limulus SAP, and the derived amino acid sequence, the first invertebrate SAP-like pentraxin sequence, have been determined. Two sequences were identified that differed only in the length of the 3' untranslated region.