Surface plasmon resonance imaging coupled to on-chip mass spectrometry: a new tool to probe protein-GAG interactions.

A biosensor device for the detection and characterization of protein-glycosaminoglycan interactions is being actively sought and constitutes the key to identifying specific carbohydrate ligands, an important issue in glycoscience. Mass spectrometry (MS) hyphenated methods are promising approaches for carbohydrate enrichment and subsequent structural characterization. In the study herein, we report the analysis of interactions between the glycosaminoglycans (GAGs) heparin (HP) and heparan sulfate (HS) and various cytokines by coupling surface plasmon resonance imaging (SPRi) for thermodynamic analysis method and MALDI-TOF MS for structural determination. To do so, we developed an SPR biochip in a microarray format and functionalized it with a self-assembled monolayer of short poly(ethylene oxide) chains for grafting the human cytokines stromal cell-derived factor-1 (SDF-1α), monocyte chemotactic protein-1 (MCP-1), and interferon-γ. The thermodynamic parameters of the interactions between these cytokines and unfractionated HP/HS and derived oligosaccharides were successively determined using SPRi monitoring, and the identification of the captured carbohydrates was carried out directly on the biochip surface using MALDI-TOF MS, revealing cytokine preferential affinity for GAGs. The MS identification was enhanced by on-chip digestion of the cytokine-bound GAGs with heparinase, leading to the detection of oligosaccharides likely involved in the binding sequence of GAG ligands. Although several carbohydrate array-based assays have been reported, this study is the first report of the successful analysis of protein-GAG interactions using SPRi-MS coupling.

A novel CFHR1-CFHR5 hybrid leads to a familial dominant C3 glomerulopathy.

The intrinsic similarity shared between the members of the complement factor H family, which comprises complement factor H and five complement factor H-related (CFHR) genes, leads to various recombination events. In turn these events lead to deletions of some genes or abnormal proteins, which are found in patients with atypical hemolytic uremic syndrome or C3 glomerulopathies. Here we describe a novel genetic rearrangement generated from a heterozygous deletion spanning 146 Kbp involving multiple CFHR genes leading to a CFHR1-R5 hybrid protein. This deletion was found in four family members presenting with a familial dominant glomerulopathy histologically classified as an overlap of dense deposit disease and C3 glomerulonephritis. Affected patients exhibited permanently low C3 and factor B levels and high amounts of activation fragments sC5b9 and Bb, indicating a systemic alternative pathway dysregulation. The abnormal protein, characterized by Western blot and immunoprecipitation, was shown to circulate in association with CFHR1 and CFHR2, attributable to its two N-terminal dimerization motifs. The presence of this protein is associated with a perturbation of Factor H activity on the C3 convertase decay. Thus, our study highlights the role of CFHRs in the physiopathology of C3 glomerulopathies and stresses the importance of screening CFHRs in all familial C3 glomerulopathies. Such hybrids described till now were always associated with familial forms.

Efficient recovery of glycosaminoglycan oligosaccharides from polyacrylamide gel electrophoresis combined with mass spectrometry analysis.

To promote efficient separation and structural analysis of glycosaminoglycan oligosaccharides, we developed a straightforward method that combined gel electrophoresis and mass spectrometry (MS). Potential limitations of this approach (e.g., low extraction yields and weak compatibility with MS) were resolved by developing an active extraction procedure that yielded a quantitative amount of sulfated oligosaccharides from excised gel bands. The compatibility of obtained oligosaccharides for subsequent MS analysis was ensured using a single, simple clean-up step on a mixed C18/graphite carbon solid-phase column that was fully effective for polymerization degrees ranging from di- to dodecasaccharides. The reported combination of carbohydrates-polyacrylamide gel electrophoresis with MS was successfully applied to glucosamino- (heparin) and galactosamino- (dermantan sulfate) glycans, demonstrating the potential of our method for structural analysis of bioactive sulfated carbohydrates extracted from biological matrices. Graphical Abstract ᅟ.

Probing the solution structure of Factor H using hydroxyl radical protein footprinting and cross-linking.

The control protein Factor H (FH) is a crucial regulator of the innate immune complement system, where it is active on host cell membranes and in the fluid phase. Mutations impairing the binding capacity of FH lead to severe autoimmune diseases. Here, we studied the solution structure of full-length FH, in its free state and bound to the C3b complement protein. To do so, we used two powerful techniques, hydroxyl radical protein footprinting (HRPF) and chemical cross-linking coupled with mass spectrometry (MS), to probe the structural rearrangements and to identify protein interfaces. The footprint of C3b on the FH surface matches existing crystal structures of C3b complexed with the N- and C-terminal fragments of FH. In addition, we revealed the position of the central portion of FH in the protein complex. Moreover, cross-linking studies confirmed the involvement of the C-terminus in the dimerization of FH.

Expression of recombinant human complement C1q allows identification of the C1r/C1s-binding sites.

Complement C1q is a hexameric molecule assembled from 18 polypeptide chains of three different types encoded by three genes. This versatile recognition protein senses a wide variety of immune and nonimmune ligands, including pathogens and altered self components, and triggers the classical complement pathway through activation of its associated proteases C1r and C1s. We report a method for expression of recombinant full-length human C1q involving stable transfection of HEK 293-F mammalian cells and fusion of an affinity tag to the C-terminal end of the C chain. The resulting recombinant (r) C1q molecule is similar to serum C1q as judged from biochemical and structural analyses and exhibits the characteristic shape of a bunch of flowers. Analysis of its interaction properties by surface plasmon resonance shows that rC1q retains the ability of serum C1q to associate with the C1s-C1r-C1r-C1s tetramer, to recognize physiological C1q ligands such as IgG and pentraxin 3, and to trigger C1r and C1s activation. Functional analysis of rC1q variants carrying mutations of LysA59, LysB61, and/or LysC58, in the collagen-like stems, demonstrates that LysB61 and LysC58 each play a key role in the interaction with C1s-C1r-C1r-C1s, with LysA59 being involved to a lesser degree. We propose that LysB61 and LysC58 both form salt bridges with outer acidic Ca(2+) ligands of the C1r and C1s CUB (complement C1r/C1s, Uegf, bone morphogenetic protein) domains. The expression method reported here opens the way for deciphering the molecular basis of the unusual binding versatility of C1q by mapping the residues involved in the sensing of its targets and the binding of its receptors.

On-line capillary isoelectric focusing hyphenated to native electrospray ionization mass spectrometry for the characterization of interferon-γ and variants.

The on-line hyphenation of Capillary IsoElectric Focusing (CIEF) with ElectroSpray Ionization Mass Spectrometry (ESI/MS) has been carried out in a non-denaturing detection mode at the CIEF-MS interface. This CIEF-MS coupling methodology relied on the use of 40% glycerol-water medium as anti-convective agent in the CE capillary and the addition of 10 mM ammonium acetate buffer, pH 5, as a volatile aqueous sheath liquid. These CIEF-MS coupling conditions allowed the characterization of the highly basic cytokine human interferon-gamma (IFN-γ) and its detection as a non-covalent homodimer (33,814.3 g mol(-1)) corresponding to the active form of this immune-regulatory protein. An experimental pI value of 9.95 was determined for the human IFN-γ homodimer in these conditions. The CIEF-MS analysis of several variants bearing punctual or deletion mutations within the two D1 and D2 basic clusters at the C-terminal end of IFN-γ revealed the different contribution of these domains to the charge properties of this heparan sulfate-binding protein.

Biomarkers probed in saliva by surface plasmon resonance imaging coupled to matrix-assisted laser desorption/ionization mass spectrometry in array format.

Detection of protein biomarkers is of major interest in proteomics. This work reports the analysis of protein biomarkers directly from a biological fluid, human saliva, by surface plasmon resonance imaging coupled to mass spectrometry (SPRi-MS), using a functionalized biochip in an array format enabling multiplex SPR-MS analysis. The SPR biochip presented a gold surface functionalized by a self-assembled monolayer of short poly(ethylene oxide) chains carrying an N-hydroxysuccinimide end-group for the immobilization of antibodies. The experiments were accomplished without any sample pre-purification or spiking with the targeted biomarkers. SPRi monitoring of the interactions, immune capture from the biochip surface, and finally on-chip matrix-assisted laser desorption/ionization-MS structural identification of two protein biomarkers, salivary α-amylase and lysozyme, were successively achieved directly from saliva at the femtomole level. For lysozyme, the on-chip MS identification was completed by a proteomic analysis based on an on-chip proteolysis procedure and a peptide mass fingerprint.

Derivatization strategies for CE-LIF analysis of biomarkers: Toward a clinical diagnostic of familial transthyretin amyloidosis.

We report three derivatization strategies for CE analysis with LIF detection (CE-LIF) of two synthetic peptides mimicking the wild and mutated fragments of interest for the diagnosis of familial transthyretin amyloidosis. The precapillary derivatization of the peptides with three optical tags, 5-carboxytetramethylrhodamin succinimidyl ester (TAMRA-SE), naphtalene-2,3-dicarboxyaldehyde (NDA), and 3-(2-furoyl)quinoline-2-carboxyaldehyde (FQ) has been investigated by CE-LIF detection and MS. Results provide evidence that high reaction yields have been reached whereas the multitagging phenomenon has occurred for both NDA and TAMRA-SE labeling procedures. The derivatization and electrokinetic separation of a mixture of the two peptides of interest for the pathology diagnosis (22-aa peptides that differ only from one amino acid) were achieved using both approaches. The highest resolution with a value of 2.5 was obtained with TAMRA-SE labeled derivatives whereas NDA gave the best detection sensitivity (LOD of 2.5 µM). The validation of the developed methods showed a good linearity (R ≥ 0.997) between the peak area of the labeled derivatives and the peptide concentration for both NDA and FQ labeling procedures. The intraday RSDs of A and the migration times were less than 3.8 and 2.2%, respectively.

The nano-bio interface mapped by oxidative footprinting of the adsorption sites of myoglobin.

Oxidative footprinting has been used to study the structure of macromolecular assemblies such as protein-protein and protein-ligand complexes. We propose a novel development of this technique to probe the protein corona that forms at the surface of nanoparticles in any biological medium. Indeed, very few techniques allow studying this interface at the molecular and residue level. Based on hydroxyl radical-mediated oxidation of proteins and analysis by nanoscale liquid chromatography coupled to tandem mass spectrometry (nanoLC-MS/MS), two sites of adsorption of myoglobin on silica nanoparticles are identified. This method gives new insights in the understanding of protein adsorption on nanomaterials.

Structure and functional impact of glycosaminoglycan modification of HSulf-2 endosulfatase revealed by atomic force microscopy and mass spectrometry.

The human sulfatase HSulf-2 is one of only two known endosulfatases that play a decisive role in modulating the binding properties of heparan sulfate proteoglycans on the cell surface and in the extracellular matrix. Recently, HSulf-2 was shown to exhibit an unusual post-translational modification consisting of a sulfated glycosaminoglycan chain. This study describes the structural characterization of this glycosaminoglycan (GAG) and provides new data on its impact on the catalytic properties of HSulf-2. The unrevealed nature of this GAG chain is identified as a chondroitin/dermatan sulfate (CS/DS) mixed chain, as shown by mass spectrometry combined with NMR analysis. It consists primarily of 6-O and 4-O monosulfated disaccharide units, with a slight predominance of the 4-O-sulfation. Using atomic force microscopy, we show that this unique post-translational modification dramatically impacts the enzyme hydrodynamic volume. We identified human hyaluronidase-4 as a secreted hydrolase that can digest HSulf-2 GAG chain. We also showed that HSulf-2 is able to efficiently 6-O-desulfate antithrombin III binding pentasaccharide motif, and that this activity was enhanced upon removal of the GAG chain. Finally, we identified five N-glycosylation sites on the protein and showed that, although required, reduced N-glycosylation profiles were sufficient to sustain HSulf-2 integrity.

Linking the proteins--elucidation of proteome-scale networks using mass spectrometry.

Proteomes are intricate. Typically, thousands of proteins interact through physical association and post-translational modifications (PTMs) to give rise to the emergent functions of cells. Understanding these functions requires one to study proteomes as "systems" rather than collections of individual protein molecules. The abstraction of the interacting proteome to "protein networks" has recently gained much attention, as networks are effective representations, that lose specific molecular details, but provide the ability to see the proteome as a whole. Mostly two aspects of the proteome have been represented by network models: proteome-wide physical protein-protein-binding interactions organized into Protein Interaction Networks (PINs), and proteome-wide PTM relations organized into Protein Signaling Networks (PSNs). Mass spectrometry (MS) techniques have been shown to be essential to reveal both of these aspects on a proteome-wide scale. Techniques such as affinity purification followed by MS have been used to elucidate protein-protein interactions, and MS-based quantitative phosphoproteomics is critical to understand the structure and dynamics of signaling through the proteome. We here review the current state-of-the-art MS-based analytical pipelines for the purpose to characterize proteome-scale networks.

Analysis of human C1q by combined bottom-up and top-down mass spectrometry: detailed mapping of post-translational modifications and insights into the C1r/C1s binding sites.

C1q is a subunit of the C1 complex, a key player in innate immunity that triggers activation of the classical complement pathway. Featuring a unique structural organization and comprising a collagen-like domain with a high level of post-translational modifications, C1q represents a challenging protein assembly for structural biology. We report for the first time a comprehensive proteomics study of C1q combining bottom-up and top-down analyses. C1q was submitted to proteolytic digestion by a combination of collagenase and trypsin for bottom-up analyses. In addition to classical LC-MS/MS analyses, which provided reliable identification of hydroxylated proline and lysine residues, sugar loss-triggered MS(3) scans were acquired on an LTQ-Orbitrap (Linear Quadrupole Ion Trap-Orbitrap) instrument to strengthen the localization of glucosyl-galactosyl disaccharide moieties on hydroxylysine residues. Top-down analyses performed on the same instrument allowed high accuracy and high resolution mass measurements of the intact full-length C1q polypeptide chains and the iterative fragmentation of the proteins in the MS(n) mode. This study illustrates the usefulness of combining the two complementary analytical approaches to obtain a detailed characterization of the post-translational modification pattern of the collagen-like domain of C1q and highlights the structural heterogeneity of individual molecules. Most importantly, three lysine residues of the collagen-like domain, namely Lys(59) (A chain), Lys(61) (B chain), and Lys(58) (C chain), were unambiguously shown to be completely unmodified. These lysine residues are located about halfway along the collagen-like fibers. They are thus fully available and in an appropriate position to interact with the C1r and C1s protease partners of C1q and are therefore likely to play an essential role in C1 assembly.

Performance evaluation on a wide set of matrix-assisted laser desorption ionization matrices for the detection of oligosaccharides in a high-throughput mass spectrometric screening of carbohydrate depolymerizing enzymes.

Compared to other analytical methods, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) presents several unique advantages for the structural characterization of degradation products of carbohydrates. Our final goal is to implement this technique as a high-throughput platform, with the aim of exploring natural bio-diversity to discover new carbohydrate depolymerizing enzymes. In this approach, a variety of carbohydrates will be used as enzymes substrates and MALDI-MS will be employed to monitor the oligosaccharides produced. One drawback of MALDI, however, is that the choice of the matrix is largely dependent on the chemical properties of the analyte. In this context, our objective in the present work was to find the smallest set of MALDI matrices able to detect chemically heterogeneous oligosaccharides. This was done through the performance evaluation of more than 40 MALDI matrices preparations. Homogeneity of analyte-matrix deposits was considered as a critical feature, especially since the final objective is to fully automate the analyses. Evaluation of the matrices was done by means of a rigorous statistical approach. Amongst all tested compounds, our work proposes the use of the DHB/DMA ionic matrix as the most generic matrix, for rapid detection of a variety of polysaccharides including neutral, anionic, methylated, sulfated, and acetylated compounds. The selected matrices were then used to screen crude bacterial incubation media for the detection of enzymatic degradation products.

HABA-based ionic liquid matrices for UV-MALDI-MS analysis of heparin and heparan sulfate oligosaccharides.

Polysulfated carbohydrates such as heparin (HP) and heparan sulfate (HS) are not easily amenable to usual ultraviolet matrix-assisted laser desorption/ionization-mass spectrometry (UV-MALDI)-MS analysis due to the thermal lability of their O- and N-SO(3) moieties, and their poor ionization efficiency with common crystalline matrices. Recently, ionic liquid matrices showed considerable advantages over conventional matrices for MALDI-MS of acidic compounds. Two new ionic liquid matrices (ILMs) based on the combination of 2-(4-hydroxyphenylazo)benzoic acid (HABA) with 1,1,3,3-tetramethylguanidine and spermine were evaluated in the study herein. Both ILMs were successfully applied to the analysis of synthetic heparin oligosaccharides of well-characterized structures as well as to heparan sulfate-derived oligosaccharides from enzymatic depolymerization. HABA-based ILMs showed improved signal-to-noise ratio as well as a decrease of fragmentation/desulfation processes and cation exchange. Sulfated oligosaccharides were detected with higher sensitivity than usual crystalline matrices, and their intact fully O- and N-sulfated species [M-Na](-) were easily observed on mass spectra. MALDI-MS characterization of challenging analytes such as heparin octasaccharide carrying 8-O and 4 N-sulfo groups, and heparin octadecasulfated dodecasaccharide was successfully achieved.

Quantitative proteomic analysis of lentiviral vectors using 2-DE.

Among the integrative gene therapy vectors developed to date, human immunodeficiency virus type 1 (HIV-1)-derived lentiviral vectors (LV) are distinguished by their capacity to infect both dividing and non-dividing cells. Recombinant LV particles contain viral proteins necessary for their packaging, infectious and integrating functions. Like the parental HIV-1 virus they are able to acquire various cellular proteins, but the number and localisation of these proteins are poorly characterised. In the present study we used 2-DE followed by MALDI-TOF to quantify the protein content of several types of vesicular stomatitis virus G-pseudotyped LV including those that were extensively purified in the perspective of clinical gene therapy studies. A proteinase K treatment was used to distinguish between cellular proteins incorporated into virions (I-proteins) and those co-purified with vectors (C-proteins). We found 10 C-proteins and 18 I-proteins associated with LV. Copy numbers for these core I-proteins varied from 5 (AIP-1/ALIX) to 280 (Cyclophilin A) per vector particle. Three novel I-proteins, guanine nucleotide-binding protein 2, L-lactate dehydrogenase B chain and hnRNP core protein A1, were found. This study defines for the first time, the protein stoichiometry of infectious HIV-1-derived LV particles.

Mass spectrometry analysis of the human endosulfatase Hsulf-2.

The human 6-O-endosulfatases HSulf-1 and -2 catalyze the region-selective hydrolysis of the 6-O-sulfate group of the glucosamine residues within sulfated domains of heparan sulfate, thereby ensuring a unique and original post-biosynthetic modification of the cell surface proteoglycans. While numerous studies point out the role of HSulf-2 in crucial physiological processes as well as in pathological conditions particularly in cancer, its structural organization in two chains and its functional properties remain poorly understood. In this study, we report the first characterization by mass spectrometry (MS) of HSulf-2. An average molecular weight of 133,115 Da was determined for the whole enzyme by MALDI-TOF MS, i.e. higher than the naked amino acid backbone (98,170 Da), highlighting a significant contribution of post-translational modifications. The HSulf-2 protein sequence was determined by Nano-LC-MS/MS, leading to 63% coverage and indicating at least four N-glycosylation sites at Asn 108, 147, 174 and 217. These results provide a platform for further structural investigations of the HSulf enzymes, aiming at deciphering the role of each chain in the substrate binding and specificities and in the catalytic activities.

Sulfated oligosaccharides (heparin and fucoidan) binding and dimerization of stromal cell-derived factor-1 (SDF-1/CXCL 12) are coupled as evidenced by affinity CE-MS analysis.

Chemokine stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant involved in leukocyte trafficking and metastasis. Heparan sulfate on the cell surface binds SDF-1 and may modulate its function as a coreceptor of this chemokine. A major effect of the glycosaminoglycan binding may be on the quaternary structure of SDF-1, which has been controversially reported as a monomer or a dimer. We have investigated the effect of sulfated oligosaccharides on the oligomerization of SDF-1 and of its mutated form SDF-1 (3/6), using affinity capillary electrophoresis (ACE) hyphenated to mass spectrometry (MS). Coupled to MS, ACE allowed the study for the first time of the effect of size-defined oligosaccharides on the quaternary organization of SDF-1 in muM range concentrations, i.e., lower values than the mM values previously reported in NMR, light scattering, and ultracentrifugation experiments. Our results showed that in the absence of sulfated oligosaccharides, SDF-1 is mostly monomeric in solution. However, dimer formation was observed upon interaction with heparin-sulfated oligosaccharides despite the mM Kd values for dimerization. A SDF-1/oligosaccharide 2/1 complex was detected, indicating that oligosaccharide binding promoted the dimerization of SDF-1. Heparin tetrasaccharide but not disaccharide promoted dimer formation, suggesting that the dimer required to be stabilized by a long enough bound oligosaccharide. The SDF-1/oligosaccharide 1/1 complex was only observed with heparin disaccharide and fucoidan pentasaccharide, pointing out the role of specific structural determinants in promoting dimer formation. These results underline the importance of dimerization induced by glycosaminoglycans for chemokine functionality.

Characterization of Renal Injury and Inflammation in an Experimental Model of Intravascular Hemolysis.

Intravascular erythrocyte destruction, accompanied by the release of pro-oxidative and pro-inflammatory components hemoglobin and heme, is a common event in the pathogenesis of numerous diseases with heterogeneous etiology and clinical features. A frequent adverse effect related to massive hemolysis is the renal injury and inflammation. Nevertheless, it is still unclear whether heme--a danger-associated molecular pattern--and ligand for TLR4 or upstream hemolysis-derived products are responsible for these effects. Well-characterized animal models of hemolysis with kidney impairment are needed to investigate how hemolysis drives kidney injury and to test novel therapeutic strategies. Here, we characterized the pathological processes leading to acute kidney injury and inflammation during massive intravascular hemolysis, using a mouse model of phenylhydrazine (PHZ)-triggered erythrocyte destruction. We observed profound changes in mRNA levels for markers of tubular damage (Kim-1, NGAL) and regeneration (indirect marker of tubular injury, Ki-67), and tissue and vascular inflammation (IL-6, E-selectin, P-selectin, ICAM-1) in kidneys of PHZ-treated mice, associated with ultrastructural signs of tubular injury. Moreover, mass spectrometry revealed presence of markers of tubular damage in urine, including meprin-α, cytoskeletal keratins, α-1-antitrypsin, and α-1-microglobulin. Signs of renal injury and inflammation rapidly resolved and the renal function was preserved, despite major changes in metabolic parameters of PHZ-injected animals. Mechanistically, renal alterations were largely heme-independent, since injection of free heme could not reproduce them, and scavenging heme with hemopexin in PHZ-administered mice could not prevent them. Reduced overall health status of the mice suggested multiorgan involvement. We detected amylasemia and amylasuria, two markers of acute pancreatitis. We also provide detailed characterization of renal manifestations associated with acute intravascular hemolysis, which may be mediated by hemolysis-derived products upstream of heme release. This analysis provides a platform for further investigations of hemolytic diseases and associated renal injury and the evaluation of novel therapeutic strategies that target intravascular hemolysis.

Interaction of TiO2 nanoparticles with proteins from aquatic organisms: the case of gill mucus from blue mussel.

To better understand the mechanisms of TiO2 nanoparticle (NP) uptake and toxicity in aquatic organisms, we investigated the interaction of NPs with the proteins found in gill mucus from blue mussels. Mucus is secreted by many aquatic organisms and is often their first line of defense against pathogens, xenobiotics, and other sources of environmental stress. Here, five TiO2 NPs and one SiO2 NP were incubated with gill mucus and run out on a one-dimensional polyacrylamide gel for a comparative qualitative analysis of the free proteins in the mucosal solution and the proteins bound to NPs. We then used nanoscale liquid chromatography coupled with tandem mass spectrometry to identify proteins of interest. Our data demonstrated dissimilar protein profiles between the crude mucosal solution and proteins adsorbed on NPs. In particular, extrapallial protein (EP), one of the most abundant mucus proteins, was absent from the adsorbed proteins. After thermal denaturation experiments, this absence was attributed to the EP content in aromatic amino acids that prevents protein unfolding and thus adsorption on the NP. Moreover, although the majority of the protein corona was qualitatively similar across the NPs tested here (SiO2 and TiO2), a few proteins in the corona showed a specific recruitment pattern according to the NP oxide (TiO2 vs SiO2) or crystal structure (anatase TiO2 vs rutile TiO2). Therefore, protein adsorption may vary with the type of NP. Graphical abstract Proteins with adsorption selectivity as identified from isolated bands.

The chondroitin sulfate/dermatan sulfate 4-O-endosulfatase from marine bacterium Vibrio sp FC509 is a dimeric species: Biophysical characterization of an endosulfatase.

Sulfatases catalyze hydrolysis of sulfate groups. They have a key role in regulating the sulfation states that determine the function of several scaffold molecules. Currently, there are no studies of the conformational stability of endosulfatases. In this work, we describe the structural features and conformational stability of a 4-O-endosulfatase (EndoV) from a marine bacterium, which removes specifically the 4-O-sulfate from chondroitin sulfate/dermatan sulfate. For that purpose, we have used several biophysical techniques, namely, fluorescence, circular dichroism (CD), FTIR spectroscopy, analytical ultracentrifugation (AUC), differential scanning calorimetry (DSC), mass spectrometry (MS), dynamic light scattering (DLS) and size exclusion chromatography (SEC). The protein was a dimer with an elongated shape. EndoV acquired a native-like structure in a narrow pH range (7.0-9.0); it is within this range where the protein shows the maximum of enzymatic activity. The dimerization did not involve the presence of disulphide-bridges as suggested by AUC, SEC and DLS experiments in the presence of ß-mercaptoethanol (ß-ME). EndoV secondary structure is formed by a mixture of α and ß-sheet topology, as judged by deconvolution of CD and FTIR spectra. Thermal and chemical denaturations showed irreversibility and the former indicates that protein did not unfold completely during heating.