Effects of calcium, magnesium, and phosphorylcholine on secondary structures of human C-reactive protein and serum amyloid P component observed by infrared spectroscopy

Nanocrystalline diamond sensor targeted for selective CRP detection: an ATR-FTIR spectroscopy study

Protein immobilization on functionalized fluorine-terminated nanocrystalline (NCD) films was studied by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy using an immobilization protocol developed to specifically bind C-reactive protein (CRP). Using an ATR-FTIR spectroscopy method employing a force-controlled anvil-type configuration, three critical steps of the ex situ CRP immobilization were analyzed. First, the NCD surface was passivated by deposition of a copolymer layer consisting of polyethylene oxide and polypropylene oxide. Second, a synthetic modified polypeptide binder with high affinity to CRP was covalently attached to the polymeric film. Third, CRP dissolved in aqueous buffer in concentrations of 10-20 μg/mL was added on the functionalized NCD surface. Both the amide I and II bands, due to the polypeptide binder and CRP, were clearly observed in ATR-FTIR spectra. CRP amide I bands were extracted from difference spectra and yielded bands that agreed well with the reported amide I band of free (non-bonded) CRP in solution. Thus, our results show that CRP retains its secondary structure when it is attached to the polypeptide binders. Compared to previous IR studies of CRP in solution, about 200 times lower concentration was applied in the present study. Graphical Abstract Direct non-destructive ATR-FTIR analysis of C-reactive protein (CRP) selectively bound to functionalized nanocrystalline diamond (NCD) sensor surface.

Solubilization and purification of recombinant modified C-reactive protein from inclusion bodies using reversible anhydride modification

The precise function of C-reactive protein (CRP) as a regulator of inflammation in health and disease continues to evolve. The true understanding of its role in host defense responses has been hampered by numerous reports of comparable systems with contradictory interpretations of CRP as a stimulator, suppressor, or benign contributor to such processes. These discrepancies may be explained in part by the existence of a naturally occurring CRP isoform, termed modified CRP (i.e., mCRP), that is expressed when CRP subunits are dissociated into monomeric structures. The free mCRP subunit undergoes a non-proteolytic conformational change that has unique solubility, antigenicity, and bioactivity compared to the subunits that remain associated in the native, pentameric CRP molecule (i.e., pCRP). As specific reagents have been developed to identify and quantify mCRP, it has become apparent that this isoform can be formed spontaneously in calcium-free solutions. Furthermore, mCRP can be expressed on perturbed cell membranes with as little as 24–48 h incubation in tissue culture. Because mCRP has the same size as pCRP subunits as evaluated by SDS-PAGE, its presence in a pCRP reagent would not be apparent using this technique to evaluate purity. Finally, because many antibody reagents purported to be specific for “CRP” contains some, or substantial specificity to mCRP, antigen-detection techniques using such reagents may fail to distinguish the specific CRP isoform detected. All these caveats concerning CRP structures and measurements suggest that the aforementioned contradictory studies may reflect to some extent on distinctive bioactivities of mCRP rather than on pCRP. To provide a reliable, abundant supply of mCRP for separate and comparable studies, a recombinant protein was engineered and expressed in E. coli (i.e., recombinant mCRP or r_mCRP). Synthesized protein was produced as inclusion bodies which proved difficult to solubilize for purification and characterization. Herein, we describe a method using anhydride reagents to effectively solubilize r_mCRP and allow for chromatographic purification in high yield and free of contaminating endotoxin. Furthermore, the purified r_mCRP reagent represents an excellent comparable protein to the biologically produced mCRP and as a distinctive reagent from pCRP. Deciphering the true function of CRP in both health and disease requires a knowledge, understanding, and reliable supply of each of its structures so to define the distinctive effects of each on the body’s response to tissue damaging events.

Dietary magnesium intake is inversely associated with serum C-reactive protein levels: meta-analysis and systematic review

BACKGROUND/OBJECTIVES

The aim of this study was to quantitatively summarize the association of dietary magnesium (Mg) intake with serum C-reactive protein (CRP) levels in the general population.

SUBJECTS/METHODS

Observational and experimental studies through February 2013 were reviewed in PubMed and EMBASE. Additional information was retrieved through Google or hand search of related reference lists. The main outcome is either adjusted geometric mean of CRP or odds ratio (OR) of having serum CRP ≥ 3 mg/l. Meta-regression was used to determine the linear association of dietary Mg intake and adjusted geometric means of CRP levels. A fixed-effects model was used to pool ORs of interest, comparing those in the lowest with those in the highest group of dietary Mg intake.

RESULTS

A data set derived from seven cross-sectional studies including 32,918 participants was quantitatively assessed. A weighted inverse association between Mg intake and serum CRP levels was observed (β-coefficient: -0.0028; 95% confidence interval (CI), -0.0043 to -0.0013; P(trend) = 0.001) from four cross-sectional studies. The pooled OR (95% CI) of having CRP ≥ 3 mg/l was 1.49 (1.18-1.89) on comparing the lowest to the highest group of Mg intake from three studies with the data available. Qualitative assessment among five intervention studies also showed a potential beneficial effect of Mg intake on serum CRP levels.

CONCLUSIONS

This meta-analysis and systematic review indicates that dietary Mg intake is significantly and inversely associated with serum CRP levels. The potential beneficial effect of Mg intake on chronic diseases may be, at least in part, explained by inhibiting inflammation.

A single amino acid substitution in the hemagglutinin of H3N2 subtype influenza A viruses is associated with resistance to the long pentraxin PTX3 and enhanced virulence in mice

The long pentraxin, pentraxin 3 (PTX3), can play beneficial or detrimental roles during infection and disease by modulating various aspects of the immune system. There is growing evidence to suggest that PTX3 can mediate antiviral activity in vitro and in vivo. Previous studies demonstrated that PTX3 and the short pentraxin serum amyloid P express sialic acids that are recognized by the hemagglutinin (HA) glycoprotein of certain influenza A viruses (IAV), resulting in virus neutralization and anti-IAV activity. In this study, we demonstrate that specificity of both HA and the viral neuraminidase for particular sialic acid linkages determines the susceptibility of H1N1, H3N2, and H7N9 strains to the antiviral activities of PTX3 and serum amyloid P. Selection of H3N2 virus mutants resistant to PTX3 allowed for identification of amino acid residues in the vicinity of the receptor-binding pocket of HA that are critical determinants of sensitivity to PTX3; this was supported by sequence analysis of a range of H3N2 strains that were sensitive or resistant to PTX3. In a mouse model of infection, the enhanced virulence of PTX3-resistant mutants was associated with increased virus replication and elevated levels of proinflammatory cytokines in the airways, leading to pulmonary inflammation and lung injury. Together, these studies identify determinants in the viral HA that can be associated with sensitivity to the antiviral activities of PTX3 and highlight its importance in the control of IAV infection.

Serum amyloid P is a sialylated glycoprotein inhibitor of influenza A viruses

Members of the pentraxin family, including PTX3 and serum amyloid P component (SAP), have been reported to play a role in innate host defence against a range of microbial pathogens, yet little is known regarding their antiviral activities. In this study, we demonstrate that human SAP binds to human influenza A virus (IAV) strains and mediates a range of antiviral activities, including inhibition of IAV-induced hemagglutination (HA), neutralization of virus infectivity and inhibition of the enzymatic activity of the viral neuraminidase (NA). Characterization of the anti-IAV activity of SAP after periodate or bacterial sialidase treatment demonstrated that α(2,6)-linked sialic acid residues on the glycosidic moiety of SAP are critical for recognition by the HA of susceptible IAV strains. Other proteins of the innate immune system, namely human surfactant protein A and porcine surfactant protein D, have been reported to express sialylated glycans which facilitate inhibition of particular IAV strains, yet the specific viral determinants for recognition of these inhibitors have not been defined. Herein, we have selected virus mutants in the presence of human SAP and identified specific residues in the receptor-binding pocket of the viral HA which are critical for recognition and therefore susceptibility to the antiviral activities of SAP. Given the widespread expression of α(2,6)-linked sialic acid in the human respiratory tract, we propose that SAP may act as an effective receptor mimic to limit IAV infection of airway epithelial cells.

Pentraxins and Fc receptors

Pentraxins are innate pattern recognition molecules whose major function is to bind microbial pathogens or cellular debris during infection and inflammation and, by doing so, contribute to the clearance of necrotic cells as well as pathogens through complement activations. Fc receptors are the cellular mediators of antibody functions. Although conceptually separated, both pentraxins and antibodies are important factors in controlling acute and chronic inflammation and infections. In recent years, increasing experimental evidence suggests a direct link between the innate pentraxins and humoral Fc receptors. Specifically, both human and mouse pentraxins recognize major forms of Fc receptors in solution and on cell surfaces with affinities similar to antibodies binding to their low affinity Fc receptors. Like immune complex, pentraxin aggregation and opsonization of pathogen result in Fc receptor and macrophage activation. The recently published crystal structure of human serum amyloid P (SAP) in complex with FcγRIIA further illustrated similarities to antibody recognition. These recent findings implicate a much broader role than complement activation for pentraxins in immunity. This review summarizes the structural and functional work that bridge the innate pentraxins and the adaptive Fc receptor functions. In many ways, pentraxins can be regarded as innate antibodies.

Exposing a hidden functional site of C-reactive protein by site-directed mutagenesis

C-reactive protein (CRP) is a cyclic pentameric protein whose major binding specificity, at physiological pH, is for substances bearing exposed phosphocholine moieties. Another pentameric form of CRP, which exists at acidic pH, displays binding activity for oxidized LDL (ox-LDL). The ox-LDL-binding site in CRP, which is hidden at physiological pH, is exposed by acidic pH-induced structural changes in pentameric CRP. The aim of this study was to expose the hidden ox-LDL-binding site of CRP by site-directed mutagenesis and to generate a CRP mutant that can bind to ox-LDL without the requirement of acidic pH. Mutation of Glu(42), an amino acid that participates in intersubunit interactions in the CRP pentamer and is buried, to Gln resulted in a CRP mutant (E42Q) that showed significant binding activity for ox-LDL at physiological pH. For maximal binding to ox-LDL, E42Q CRP required a pH much less acidic than that required by wild-type CRP. At any given pH, E42Q CRP was more efficient than wild-type CRP in binding to ox-LDL. Like wild-type CRP, E42Q CRP remained pentameric at acidic pH. Also, E42Q CRP was more efficient than wild-type CRP in binding to several other deposited, conformationally altered proteins. The E42Q CRP mutant provides a tool to investigate the functions of CRP in defined animal models of inflammatory diseases including atherosclerosis because wild-type CRP requires acidic pH to bind to deposited, conformationally altered proteins, including ox-LDL, and available animal models may not have sufficient acidosis or other possible modifiers of the pentameric structure of CRP at the sites of inflammation.

Predicting the disruption by UO2(2+) of a protein-ligand interaction

The uranyl cation (UO(2) (2+)) can be suspected to interfere with the binding of essential metal cations to proteins, underlying some mechanisms of toxicity. A dedicated computational screen was used to identify UO(2) (2+) binding sites within a set of nonredundant protein structures. The list of potential targets was compared to data from a small molecules interaction database to pinpoint specific examples where UO(2) (2+) should be able to bind in the vicinity of an essential cation, and would be likely to affect the function of the corresponding protein. The C-reactive protein appeared as an interesting hit since its structure involves critical calcium ions in the binding of phosphorylcholine. Biochemical experiments confirmed the predicted binding site for UO(2) (2+) and it was demonstrated by surface plasmon resonance assays that UO(2) (2+) binding to CRP prevents the calcium-mediated binding of phosphorylcholine. Strikingly, the apparent affinity of UO(2) (2+) for native CRP was almost 100-fold higher than that of Ca(2+). This result exemplifies in the case of CRP the capability of our computational tool to predict effective binding sites for UO(2) (2+) in proteins and is a first evidence of calcium substitution by the uranyl cation in a native protein.

Magnesium and C-reactive protein in heart failure: an anti-inflammatory effect of magnesium administration?

BACKGROUND

Little is known about the relationship between serum magnesium (Mg) and C-reactive protein (CRP) in heart failure (HF).

AIM OF THE STUDY

To investigate the relationship, if any, between serum Mg and CRP in HF patients and, concomitantly, to test a hypothesis that Mg supplementation might affect serum CRP levels.

METHODS

Serum Mg and CRP were evaluated in 68 patients with chronic systolic HF leading to hospital admission and 65 patients requiring hospitalization for other causes. Following 5 weeks, serum Mg, CRP and intracellular Mg were reevaluated in 17 HF patients after administration of oral Mg citrate 300 mg/day (group A), and 18 untreated HF patients (group B). In order to obtain Gaussian distribution, logarithmic transformation of CRP was performed.

RESULTS

Inverse correlation was found between serum Mg and log CRP (r = -0.28, P = 0.002). Compared to controls, patients with HF demonstrated higher baseline CRP levels, independent of coexisting conditions, and lower serum Mg values. Following Mg treatment, log CRP decreased from 1.4 +/- 0.4 to 0.8 +/- 0.3 in group A (P < 0.001). No significant changes in log CRP were demonstrable in group B. Serum Mg (mmol/l) rose significantly in group A (0.74 +/- 0.04-0.88 +/- 0.08, P < 0.001), and to a lesser extent in group B (0.82 +/- 0.08-0.88 +/- 0.08, P = 0.04). Intracellular Mg significantly increased only in Mg-treated group A (P = 0.01).

CONCLUSIONS

Oral Mg supplementation to HF patients significantly attenuates blood levels of CRP, a biomarker of inflammation. Targeting the inflammatory cascade by Mg administration might prove a useful tool for improving the prognosis in HF.

Fiber optic biosensor for the detection of C-reactive protein and the study of protein binding kinetics

Application of a fiber optic biosensor (FOB) to the real-time investigation of the interaction kinetics between FITC-conjugated monoclonal sheep anti-human C-reactive protein (CRP) antibody and CRP isoforms on the surface of optical fiber is described. Recently, both the native pentameric CRP (pCRP), an acute phase protein belonging to pentraxin family, and an isoform of pCRP, modified CRP (mCRP), have been suggested to have proinflammation effects on vascular cells in acute myocardial infarction (AMI). In current studies, we generate mCRP from pCRP, and use several methods including fluorescence spectral properties, circular dichroism, analytical ultracentrifuge, and Western blotting to demonstrate their differences in physical and chemical properties as well as the purity of pCRP and mCRP. In addition, we design and implement an FOB to study the real-time qualitative and quantitative biomolecular recognition of CRP isoforms. Specifically, the association and dissociation rate constants of the reaction between FITC-conjugated monoclonal sheep anti-human CRP antibody and the pCRP and mCRP are determined. The feasibility of our current approach to measure the association and dissociation rate constants of the reaction between tested CRP isoforms was successfully demonstrated.

Hypomagnesemia, oxidative stress, inflammation, and metabolic syndrome

BACKGROUND

Although hypomagnesemia, oxidative stress, and inflammation are involved in the pathogenesis of cardiovascular diseases, there is not a previous description concerning their potential interaction; thus, the aim of this study was to examine the relationship between metabolic syndrome (MetS), hypomagnesemia, inflammation, and oxidative stress.

METHODS

Case-control design study. Incident cases of MetS (84 women and 63 men) were compared with healthy control subjects (163 women and 131 men) matched by age and gender. MetS was diagnosed according to the Adult Treatment Panel III (ATP III) criterion. Oxidative stress was defined by serum malondialdehyde concentration (MDA) > or =50 mg/dL, low-grade chronic inflammation by C-reactive protein (CRP) serum levels > or =3 mg/L, and hypomagnesemia by serum magnesium concentrations < or =1.8 mg/dL.

RESULTS

Multivariate analysis adjusted by age, sex, body mass index, waist-to-hip ratio, and total adiposity showed a strong association between MetS and hypomagnesemia (OR 1.9; 95% CI 1.3-7.1), inflammation (OR 1.7; 95% CI 1.4-8.4), and oxidative stress (OR 1.4; 95% CI 0.9-12.6). Additional adjustment by CRP levels showed that MetS remained associated to hypomagnesemia (OR 1.4; 95% CI 1.1-5.9) but not to oxidative stress (OR 1.1; 95% CI 0.9-5.9), and adjusted by MDA levels, MetS remained strongly associated to hypomagnesemia (1.6; CI 95% 1.1-7.4), but not to inflammation (OR 1.05; 95% CI 0.97-14.2). Adjusted by serum magnesium levels, inflammation (OR 1.2; 95% CI 1.1-9.1) and oxidative stress (OR 1.1; 95% CI 1.1-9.7) were slightly associated to MetS.

CONCLUSIONS

The interaction of inflammation and oxidative stress is related and increases the risk for MetS, whereas serum magnesium levels and MetS are independently associated.

Binding of Ca2+, Mg2+, and heparin by human serum amyloid P component in affinity capillary electrophoresis

Human serum amyloid P component (SAP) is a glycoprotein circulating in the blood and found in association with all types of amyloid (malfolded potein aggregates) examined so far. Despite uncertainties regarding the precise function of SAP in vivo, the lectin-like properties of this Ca(2+)-activated protein with affinity for anionic saccharides and malfolded proteins are well known. The propensity to form homomeric penta- or decamers in solution and the selfaggregation in the presence of Ca(2+) as well as the tendency of SAP to attach to uncoated fused silica have precluded the analysis of SAP by microelectrophoretic methods. We now work out conditions to characterize the binding of Ca(2+) and Mg(2+) and the binding of heparin to SAP in the presence of divalent metal ions by ACE. The results show a strong binding of heparin (sub-muM apparent dissociation constants) even in the abscence of Ca(2+) at low ionic strength, pH 8.2. Also, a selective interaction with Ca(2+) compared with Mg(2+) is demonstrated. The approach will further the use of microelectrophoretic methods to examine the interactions of SAP with ligands of putative pathophysiological relevance such as lipopolysaccharides and misfolded proteins.

In situ conformational analysis of fibrinogen adsorbed on Si surfaces

Fibrinogen is a major plasma protein. Previous investigations of structural changes of fibrinogen due to adsorption are mostly based on indirect evidence after its desorption, whereas our measurements were performed on fibrinogen in its adsorbed state. Specific enzyme-linked immunosorption experiments showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. Atomic force microscopy (AFM) investigations revealed the trinodular shape of fibrinogen molecules adsorbed on hydrophilic surfaces, whereas all of the molecules appeared globular on hydrophobic surfaces. The distribution of secondary structures in adsorbed fibrinogen was quantified by in situ Fourier-transform infrared (FTIR) analysis. Substrates of identical chemical bulk composition but different surface hydrophobicity permit direct comparison among them. Adsorption properties of fibrinogen are different for each degree of hydrophobicity. Although there is some increase of turn structure and decrease of beta-sheet structure, the secondary structure of adsorbed fibrinogen on hydrophilic surface turned out to be rather similar to that of the protein in solution phase with a major alpha-helix content. Hydrophilic surfaces exhibit superior blood compatibility as required for medical applications.

FTIR reveals structural differences between native beta-sheet proteins and amyloid fibrils

The presence of beta-sheets in the core of amyloid fibrils raised questions as to whether or not beta-sheet-containing proteins, such as transthyretin, are predisposed to form such fibrils. However, we show here that the molecular structure of amyloid fibrils differs more generally from the beta-sheets in native proteins. This difference is evident from the amide I region of the infrared spectrum and relates to the distribution of the phi/psi dihedral angles within the Ramachandran plot, the average number of strands per sheet, and possibly, the beta-sheet twist. These data imply that amyloid fibril formation from native beta-sheet proteins can involve a substantial structural reorganization.

Effects of CaCl2 and MgCl2 on Fourier transform infrared spectra of lung cancer cells

The cations Ca2+ and Mg2+ are two important factors in the growth and maintenance of living cells. The addition of Ca2+ to living cells can cause a change in the three-dimensional (3D) structure of calcium binding proteins. Therefore, we decided to study whether the addition of CaCl2 and MgCl2 to three in vitro growing lung cancer cell lines could cause changes that could be measured by Fourier Transform Infrared Spectroscopy. The addition of CaCl2 or MgCl2 to lung cancer cells caused an increase in absorbance of the trough at 1410 cm(-1). This translated into an inversion of the 1410/1395 cm(-1) ratio following the addition of CaCl2 or MgCl2 for all three lung cancer cell lines. Also, the amide I peak shifted from around 1631 cm(-1) to lower wavenumbers when CaCl2 or MgCl2 was added to cancer cells. Furthermore, the addition of these two substances caused a shift of the peak between 3290 and 3395 cm(-1). Finally, while the addition of CaCl2 to lung cancer cells was associated with an increased cell death, this was not the case following the addition of MgCl2. This would confirm that the changes seen in the spectra of all three cell lines are due to metabolic and ionic shifts rather than cell death.

Loss of pentameric symmetry of C-reactive protein is associated with delayed apoptosis of human neutrophils

Human neutrophil granulocytes die rapidly, and their survival is contingent upon rescue from programmed cell death by signals from the environment. Here we report that a novel signal for delaying neutrophil apoptosis is the classic acute phase reactant, C-reactive protein (CRP). However, this anti-apoptotic activity is expressed only when the cyclic pentameric structure of CRP is lost, resulting in formation of modified or monomeric CRP (mCRP), which may be formed in inflamed tissues. By contrast, native pentameric CRP and CRP peptides 77-82, 174-185, and 201-206 failed to affect neutrophil apoptosis. The apoptosis delaying action of mCRP was markedly attenuated by an antibody against the low affinity IgG immune complex receptor (CD16) but not by an anti-CD32 antibody. mCRP evoked a transient concurrent activation of the extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt signaling pathways, leading to inhibition of caspase-3 and consequently to delaying apoptosis. Consistently, pharmacological inhibition of either ERK or Akt reversed the anti-apoptotic action of mCRP; however, they did not produce additive inhibition. Thus, mCRP, but not pentameric CRP or peptides derived from CRP, promotes neutrophil survival and may therefore contribute to amplification of the inflammatory response.

C-reactive protein-mediated phagocytosis and phospholipase D signalling through the high-affinity receptor for immunoglobulin G (FcgammaRI)

C-reactive protein (CRP) is the prototypic acute-phase protein in man which performs innate immune functions. CRP-mediated phagocytosis may be indirect, through activation of complement and complement receptors, or direct, through receptors for the Fc portion of immunoglobulin G (IgG; FcgammaRs) or even a putative CRP-specific receptor. No strong evidence has been shown to indicate which receptors may be responsible for phagocytosis or signalling responses. Using BIAcore technology, we confirm that CRP binds directly to the extracellular portion of FcgammaRI with a threefold higher affinity than IgG (KD = 0.81 x 10-9 m). Binding is Ca2+ dependent and is inhibited by IgG1 but not by phosphorylcholine (PC). CRP opsonization (using CRP concentrations within the normal human serum range) of PC-conjugated sheep erythrocytes increased phagocytosis of these particles by COS-7 cells transfected with FcgammaRI-II chimaera or FcgammaRI/gamma-chain. Interferon-gamma-treated U937 cells, which signal through FcgammaRI to activate phospholipase D (PLD) in response to cross-linked IgG, were also activated by CRP without any requirement for further cross-linking. These studies indicate that CRP is capable of binding to and cross-linking FcgammaRI thereby resulting in PLD activation and increased phagocytosis. Uptake by FcgammaRI has been reported to promote various acquired immune responses suggesting that CRP could act in a similar way.

Relationship between serum magnesium levels and C-reactive protein concentration, in non-diabetic, non-hypertensive obese subjects

OBJECTIVE

To examine the association between serum magnesium levels and C-reactive protein (CRP) in non-diabetic, non-hypertensive obese subjects.

DESIGN

Cross-sectional study.

SUBJECTS

A total of 371 subjects, 101 men and 270 women. Of them 138 lean (37.2%), 133 (35.9%) overweight, and 100 (26.9%) were obese, matched by age.

MEASUREMENTS

Fasting and 2 h serum glucose following a 75 g oral glucose load. Fasting serum total cholesterol, HDL- and LDL-cholesterol, triglycerides, C-reactive protein (CRP), albumin; and magnesium levels; urinary protein excretion; body mass index (BMI), waist-to-hip ratio (WHR), and blood pressure.

RESULTS

The presence of CRP was documented in four (2.9%) lean, 13 (9.8%) overweight, and 20 (20.0%) obese subjects, and decreased magnesium levels (equal or less than 1.8 mg/dl), in 2 (1.45%) lean, 7 (5.2%) overweight, and 19 (19%) obese subjects. The lowest serum magnesium levels and the highest CRP concentrations were documented in the obese subjects. Twenty-three (82.1%) of the subjects with low serum magnesium (five overweight and 18 obese) showed CRP concentration equal or more than 10 mg/l. There was a graded significant decrease between CRP concentration and serum magnesium levels (r = -0.39, P = 0.002). The odds ratio (CI95%) between magnesium and CRP adjusted by age, sex, BMI and glucose tolerance status for the subjects within the low quartile of magnesium distribution was 2.11 (1.23-3.84).

CONCLUSION

The results of this study show that low serum magnesium levels are independently related to elevated CRP concentration, in non-diabetic, non-hypertensive obese subjects.

Comparison of the solution conformation and dynamics of antifreeze glycoproteins from Antarctic fish

The (1)H- and (13)C-NMR spectra of antifreeze glycoprotein fractions 1-5 from Antarctic cod have been assigned, and the dynamics have been measured using (13)C relaxation at two temperatures. The chemical shifts and absence of non-sequential (1)H-(1)H NOEs are inconsistent with a folded, compact structure. (13)C relaxation measurements show that the protein has no significant long-range order, and that the local correlation times are adequately described by a random coil model. Hydroxyl protons of the sugar residues were observed at low temperature, and the presence of exchange-mediated ROEs to the sugar indicate extensive hydration. The conformational properties of AFGP1-5 are compared with those of the previously examined 14-mer analog AFGP8, which contains proline residues in place of some alanine residues (Lane, A. N., L. M. Hays, R. E. Feeney, L. M. Crowe, and J. H. Crowe. 1998. Protein Sci. 7:1555-1563). The infrared (IR) spectra of AFGP8 and AFGP1-5 in the amide I region are quite different. The presence of a wide distribution of backbone torsion angles in AFGP1-5 leads to a rich spectrum of frequencies in the IR spectrum, as interconversion among conformational states is slow on the IR frequency time scale. However, these transitions are fast on the NMR chemical shift time scales. The restricted motions for AFGP8 may imply a narrower distribution of possible o, psi angles, as is observed in the IR spectrum. This has significance for attempts to quantify secondary structures of proteins by IR in the presence of extensive loops.

Secondary structure of recombinant human cystathionine beta-synthase in aqueous solution: effect of ligand binding and proteolytic truncation

The secondary structural composition and substrate-induced conformational changes of recombinant human cystathionine beta-synthase (CBS) in aqueous solution have been investigated in its full-length form (tetramer of 63-kDa subunits) by Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopies. In addition, structural comparison of a proteolytic truncated form (dimer of 45-kDa subunits) to that of the full-length enzyme has also been carried out. Second-derivative and Fourier self-deconvolutional enhanced infrared spectra revealed amide I band components ascribed to beta-sheet (1689, 1638, and 1627 cm(-1)), alpha-helix (1658 cm(-1)), beta-turn (1679 and 1668 cm(-1)), and unordered (1651 cm(-1)) structures in the spectra of the full-length enzyme. Quantitative analysis of FT-IR and CD spectra reveals that the full-length enzyme consists of about 48-53% beta-sheet, 25-30% alpha-helix, 8-10% turn, and 10-19% unordered structures. Under constraint of the spectroscopic data, theoretical prediction of locations of these secondary structural elements using Garnier's method shows that human CBS may contain a beta-sheet/alpha-helix/beta-sheet core structure. Second-derivative spectrum of the truncated enzyme exhibited all the major spectral features that are present in the full-length enzyme, indicating a preservation of the core structure of the enzyme. Significant differences were observed between the infrared spectra of the enzymes with or without the substrate, serine, indicating a substrate-induced conformational change in the enzyme, which did not result in a change in overall composition of secondary structural content based on quantitative analysis of FT-IR and far-UV CD spectra.

Ligand-binding sites in human serum amyloid P component

Amyloid P component (AP) is a naturally occurring glycoprotein that is found in serum and basement membranes. AP is also a component of all types of amyloid, including that found in individuals who suffer from Alzheimer's disease and Down's syndrome. Because AP has been found to bind strongly and specifically to certain glycosaminoglycans that are components of amyloid deposits, AP may play an important role in the maintenance of amyloid. In the present work, we isolated and identified two proteolytic fragments of AP that are responsible for its heparin-binding activity. Neither fragment corresponds to published heparin-binding sequences. The structural requirements for activity of the peptides (amino acid residues 27-38 and 192-203 of AP) were examined by means of solid-phase inhibition assays with synthetic peptides. AP-(192-203)-peptide inhibits the Ca(2+)-dependent binding of AP to heparin with an IC50 of 25 microM, while the IC50 of AP-(27-38)-peptide and AP-(33-38)-peptide are 10 microM and 2 microM, respectively. The understanding of the structure and function of active AP peptides will be useful for development of amyloid-targeted diagnostics and therapeutics.

Infrared spectroscopic studies of lyophilization- and temperature-induced protein aggregation

Recent studies have clearly demonstrated that Fourier transform IR spectroscopy can be a powerful tool for the study of protein stabilization during freeze-drying and for optimizing approaches to prevent lyophilization-induced protein aggregation. The purpose of the current review is to provide an overview of these topics, as well as an introduction to the study of protein secondary structure with IR spectroscopy. We will start with a general summary of the theories and practices for processing and interpreting protein IR spectra. We will then review the current literature on the use of IR spectroscopy to study protein structure and the effects of stabilizers during lyophilization. Next we will concentrate specifically on protein aggregation. The bulk of the research and the key assignments of spectral features in protein aggregates come from studies of the effects of high and low temperature on proteins. Therefore, we will first consider this topic. Finally, we will summarize the recent theoretical and applied work on lyophilization-induced aggregation.

Structure and function of the pentraxins

Over the past two years, the three-dimensional structure of the serum amyloid P component was defined by X-ray diffraction, the first such visualization of a pentraxin. Binding sites for calcium, ligands and complement were identified. New fusion proteins with amino acid sequence homology to the pentraxins were described, and new insights were gained into pentraxin phylogeny, biosynthesis, ligands, complement activation, leukocyte reactivity and biological functions in vivo.

The use and misuse of FTIR spectroscopy in the determination of protein structure

Fourier transform infrared (FTIR) spectroscopy is an established tool for the structural characterization of proteins. However, many potential pitfalls exist for the unwary investigator. In this review we critically assess the application of FTIR spectroscopy to the determination of protein structure by (1) outlining the principles underlying protein secondary structure determination by FTIR spectroscopy, (2) highlighting the situations in which FTIR spectroscopy should be considered the technique of choice, (3) discussing the manner in which experiments should be conducted to derive as much physiologically relevant information as possible, and (4) outlining current methods for the determination of secondary structure from infrared spectra of proteins.