Amino acid sequence of hen ovomacroglobulin (ovostatin) deduced from cloned cDNA

A New Assessment of Thioester-Containing Proteins Diversity of the Freshwater Snail Biomphalaria glabrata

Thioester-containing proteins (TEPs) superfamily is known to play important innate immune functions in a wide range of animal phyla. TEPs are involved in recognition, and in the direct or mediated killing of several invading organisms or pathogens. While several TEPs have been identified in many invertebrates, only one TEP (named BgTEP) has been previously characterized in the freshwater snail, Biomphalaria glabrata. As the presence of a single member of that family is particularly intriguing, transcriptomic data and the recently published genome were used to explore the presence of other BgTEP related genes in B. glabrata. Ten other TEP members have been reported and classified into different subfamilies: Three complement-like factors (BgC3-1 to BgC3-3), one α-2-macroblobulin (BgA2M), two macroglobulin complement-related proteins (BgMCR1, BgMCR2), one CD109 (BgCD109), and three insect TEP (BgTEP2 to BgTEP4) in addition to the previously characterized BgTEP that we renamed BgTEP1. This is the first report on such a level of TEP diversity and of the presence of macroglobulin complement-related proteins (MCR) in mollusks. Gene structure analysis revealed alternative splicing in the highly variable region of three members (BgA2M, BgCD109, and BgTEP2) with a particularly unexpected diversity for BgTEP2. Finally, different gene expression profiles tend to indicate specific functions for such novel family members.

A complex of novel protease inhibitor, ovostatin homolog, with its cognate proteases in immature mice uterine luminal fluid

A predominant gelatinolytic enzyme with approximately 26 kDa was observed in gelatin zymogram of immature mice uterine luminal fluid (ULF). Size exclusion analysis revealed that the native size of this enzyme was close to that of human α₂-macroglobulin (α₂-MG), a 725 kDa protein. This large protease was isolated by a series of chromatographic steps on the Sephacryl S-400 and DEAE-Sepharose columns. The results from gelatin zymography and SDS-PAGE analysis supported that this large protease consists of gelatinolytic enzyme and a 360 kDa protein. Through tandem mass spectrometry analysis followed by MASCOT database search, the 360 kDa protein was identified as ovostatin homolog (accession: NP_001001179.2) assigned as a homolog of chicken ovostatin, a protease inhibitor. The co-fractionation analysis by gel filtration and mouse ovostatin homolog (mOH) co-immunoprecipitation experiments demonstrated that the mOH formed a complex with three gelatinolytic enzymes in immature mice ULF. Substrate zymography analysis revealed that the mOH-associated gelatinolytic enzymes were suitable to digest type I collagen rather than type IV collagen. In addition, the refolded mOH-associated 26 kDa gelatinolytic enzyme displayed the type I collagen-digesting activity in the assay, but the other two enzymes did not have this function. RT-PCR analysis showed that mOH gene was abundantly expressed in brain, spinal cord, lung, uterus, and in 17-day embryo. Taken together, our data suggest that mOH/cognate protease system may play a potential role in regulation of tissue remodeling and fetal development.

α2-Macroglobulins: Structure and Function

α₂-macroglobulins are broad-spectrum endopeptidase inhibitors, which have to date been characterised from metazoans (vertebrates and invertebrates) and Gram-negative bacteria. Their structural and biochemical properties reveal two related modes of action: the "Venus flytrap" and the "snap-trap" mechanisms. In both cases, peptidases trigger a massive conformational rearrangement of α₂-macroglobulin after cutting in a highly flexible bait region, which results in their entrapment. In some homologs, a second action takes place that involves a highly reactive β-cysteinyl-γ-glutamyl thioester bond, which covalently binds cleaving peptidases and thus contributes to the further stabilization of the enzyme:inhibitor complex. Trapped peptidases are still active, but have restricted access to their substrates due to steric hindrance. In this way, the human α₂-macroglobulin homolog regulates proteolysis in complex biological processes, such as nutrition, signalling, and tissue remodelling, but also defends the host organism against attacks by external toxins and other virulence factors during infection and envenomation. In parallel, it participates in several other biological functions by modifying the activity of cytokines and regulating hormones, growth factors, lipid factors and other proteins, which has a great impact on physiology. Likewise, bacterial α₂-macroglobulins may participate in defence by protecting cell wall components from attacking peptidases, or in host-pathogen interactions through recognition of host peptidases and/or antimicrobial peptides. α₂-macroglobulins are more widespread than initially thought and exert multifunctional roles in both eukaryotes and prokaryotes, therefore, their on-going study is essential.

Hen egg white ovomacroglobulin promotes fibroblast migration via mediating cell adhesion and cytoskeleton

BACKGROUND

Hen egg white ovomacroglobulin (OVM) possesses a variety of bioactivities and could potentially be used as a pharmaceutical agent. It has been reported that OVM is involved in wound healing and cancer pathological processes, and previous results suggest that OVM plays a potential role in cell proliferation and migration; however, this has not yet been proven. In the present study, the effects of OVM on fibroblast proliferation and migration were evaluated.

RESULTS

Results of cell counting, cell viability, and cell cycle indicated that proliferation of fibroblasts was not altered by OVM treatment. However, scratch assays showed that OVM could promote the migration of 3 T6 mouse embryonic fibroblasts and human skin fibroblasts (HSF). Also, the adhesion of HSF to the collagen matrix was also enhanced by OVM treatment. RT-qPCR and western blot analysis showed that β1 -integrin, β-tubulin, and β-actin were up-regulated while E-cadherin was down-regulated in OVM-treated HSF cells. The effect of OVM was silenced after forming a complex with trypsin, suggesting that the protease inhibitory ability of OVM is important for its effect on cell migration.

CONCLUSION

These results suggested that promotion of OVM on cell migration was achieved by enhancing cell adhesion to extracellular matrix, reducing intercellular aggregation, and strengthening cytoskeleton. The finding of the promotion effect of OVM on cell migration is important for understanding its role in wound healing and cancer pathological processes. © 2015 Society of Chemical Industry.

Mass Spectrometry and Two-Dimensional Electrophoresis To Characterize the Glycosylation of Hen Egg White Ovomacroglobulin

Glycosylation of proteins plays an important role in their biological functions, such as allergenicity. Ovomacroglobulin (OVMG) is a glycoprotein from hen egg white, but few studies have been done so far to delineate the glycosylated sites of OVMG. The present study characterized the glycosylation of OVMG using mass spectrometry and two-dimensional electrophoresis. MALDI-TOF-MS showed that the OVMG subunit [M + H](+) ion has a peak at m/z 183297; therefore, the carbohydrate moiety is calculated as 11.5% of the whole OVMG molecule. HPLC-ESI-MS/MS confirmed that of 13 potential N-glycosylation sites of OVMG, 11 sites were glycosylated; 1 site (N(1221)) was found in both glycosylated and nonglycosylated forms. On the two-dimensional electrophoresis gel, a series of OVMG spots horizontally distributed at 170 kDa, with an isoelectric point range of 5.03-6.03, indicating the heterogeneity of glycosylation of OVMG. These results provided important information for understanding of structure, function, and potential allergenic sites of OVMG.

In-depth LC-MS/MS analysis of the chicken ovarian cancer proteome reveals conserved and novel differentially regulated proteins in humans

Ovarian cancer (OVC) remains the most lethal gynecological malignancy in the world due to the combined lack of early-stage diagnostics and effective therapeutic strategies. The development and application of advanced proteomics technology and new experimental models has created unique opportunities for translational studies. In this study, we investigated the ovarian cancer proteome of the chicken, an emerging experimental model of OVC that develops ovarian tumors spontaneously. Matched plasma, ovary, and oviduct tissue biospecimens derived from healthy, early-stage OVC, and late-stage OVC birds were quantitatively characterized by label-free proteomics. Over 2600 proteins were identified in this study, 348 of which were differentially expressed by more than twofold (p ≤ 0.05) in early- and late-stage ovarian tumor tissue specimens relative to healthy ovarian tissues. Several of the 348 proteins are known to be differentially regulated in human cancers including B2M, CLDN3, EPCAM, PIGR, S100A6, S100A9, S100A11, and TPD52. Of particular interest was ovostatin 2 (OVOS2), a novel 165-kDa protease inhibitor found to be strongly upregulated in chicken ovarian tumors (p = 0.0005) and matched plasma (p = 0.003). Indeed, RT-quantitative PCR and Western blot analysis demonstrated that OVOS2 mRNA and protein were also upregulated in multiple human OVC cell lines compared to normal ovarian epithelia (NOE) cells and immunohistochemical staining confirmed overexpression of OVOS2 in primary human ovarian cancers relative to non-cancerous tissues. Collectively, these data provide the first evidence for involvement of OVOS2 in the pathogenesis of both chicken and human ovarian cancer.

Crystallization and preliminary X-ray diffraction analysis of eukaryotic α2 -macroglobulin family members modified by methylamine, proteases and glycosidases

α2 -Macroglobulin (α2 M) has many functions in vertebrate physiology. To understand the basis of such functions, high-resolution structural models of its conformations and complexes with interacting partners are required. In an attempt to grow crystals that diffract to high or medium resolution, we isolated native human α2 M (hα2 M) and its counterpart from chicken egg white (ovostatin) from natural sources. We developed specific purification protocols, and modified the purified proteins either by deglycosylation or by conversion to their induced forms. Native proteins yielded macroscopically disordered crystals or crystals only diffracting to very low resolution (>20 Å), respectively. Optimization of native hα2 M crystals by varying chemical conditions was unsuccessful, while dehydration of native ovostatin crystals improved diffraction only slightly (10 Å). Moreover, treatment with several glycosidases hindered crystallization. Both proteins formed spherulites that were unsuitable for X-ray analysis, owing to a reduction of protein stability or an increase in sample heterogeneity. In contrast, transforming the native proteins to their induced forms by reaction either with methylamine or with peptidases (thermolysin and chymotrypsin) rendered well-shaped crystals routinely diffracting below 7 Å in a reproducible manner.

Multiple forms of alpha-2 macroglobulin in shrimp Fenneropenaeus chinesis and their transcriptional response to WSSV or Vibrio pathogen infection

Alpha-2 macroglobulin (A2M) is a non-specific protease inhibitor involved in host defense. By full length cloning and sequencing we identified three distinct cDNAs for A2M in Chinese shrimp Fenneropenaeus chinesis, designated FcA2M-1, FcA2M-2 and FcA2M-3, respectively. Expression profiles in normal tissues as well as tissues after challenge by white spot syndrome virus (WSSV) and Vibrio pathogen were conducted for FcA2M-1 and FcA2M-2. The FcA2M-1 and FcA2M-2 cDNAs encode proteins with 1501 or 1502 amino acids, respectively, containing the typical conserved domain architecture of A2M. Similar to complement component C3, FcA2M-2 has a catalytic histidine, which may confer opsonic properties on this shrimp A2M. Six variants in the bait region were found in FcA2M-2 responding differently to Vibrio challenge, thereby widening the spectrum of inhibition and the diversity of immune recognition. FcA2M-1 and FcA2M-3, as well as most other protostomia invertebrate A2Ms identified so far, have a serine residue in the catalytic histidine position instead of the conserved asparagine residue found in vertebrate A2Ms. This, as inferred from a carp C3 molecule in which the catalytic histidine is substituted by a serine, suggests A2Ms in lower invertebrates possibly bear C3-like opsonic activity. These FcA2Ms showed much lower similarity to each other than to the A2Ms in other shrimp species, further supported by pylogenetic analysis. FcA2M-1 was found to be expressed most highly in hemocytes and lymphoid organ, while FcA2M-2 was expressed most highly in the heart and lymphoid organ, with the lowest expression in hemocytes. Challenge by WSSV or Vibrio pathogen increased the FcA2M-1 mRNA level in both hemocytes and lymphoid organ. After challenge, FcA2M-2 showed up-regulation in lymphoid organ but not in hemocytes. These expression features indicate that the different types of A2M in F. chinesis carry out different functions and that they are not simply functionally redundant.

Proteases and protease inhibitors: a balance of activities in host-pathogen interaction

The immune system is the collection of effector molecules and cells of the host that act against invading parasites and their products. Secreted proteases serve important roles in parasitic metabolism and virulence and the several families of protein protease inhibitors of the plasma and blood cells play an important role in immunity by inactivating and clearing the protease virulence factors of parasites. The protease inhibitors are of two classes, the active-site inhibitors and the alpha2-macroglobulins. Inhibitors for the first class bind and inactivate the active site of the target protease. Proteins of the second class bind proteases by a unique molecular trap mechanism and deliver the bound protease to a receptor-mediated endocytic system for degradation in secondary lysosomes. Proteins of the alpha2-macroglobulin family are present in a variety of animal phyla, including the nematodes, arthropods, mollusks, echinoderms, urochordates, and vertebrates. A shared suite of unique functional characteristics have been documented for the alpha2-macroglobulins of vertebrates, arthropods, and mollusks. The alpha2-macroglobulins of nematodes, arthropods, mollusks, and vertebrates show significant sequence identity in key functional domains. Thus, the alpha2-macroglobulins comprise an evolutionarily conserved arm of the innate immune system with similar structure and function in animal phyla separated by 0.6 billion years of evolution.

The phylogeny and evolution of the thioester bond-containing proteins C3, C4 and alpha 2-macroglobulin

The complement system is an effector of both the acquired and innate immune systems of the higher vertebrates. It has been traced back at least as far as the echinoderms and so predates the appearance of the antibodies, T-cell receptors and MHC molecules of adaptive immunity. Central to the function of complement is the reaction of the thioester bond located within the structure of complement components C3 and C4. The structural thioester first appeared in a protease inhibitor, alpha 2-macroglobulin, in which it is involved in the immobilisation and entrapment of proteases. An important development in the C3 molecule has been the acquisition of a catalytic His residue which greatly increases the rate of reaction of the thioester with hydroxyl groups and with water.

Crystal structure of the receptor-binding domain of alpha 2-macroglobulin

BACKGROUND

The large plasma proteinase inhibitors of the alpha 2-macroglobulin superfamily inhibit proteinases by capturing them within a central cavity of the inhibitor molecule. After reaction with the proteinase, the alpha-macroglobulin-proteinase complex binds to the alpha-macroglobulin receptor, present in the liver and other tissues, and becomes endocytosed and rapidly removed from the circulation. The complex binds to the receptor via recognition sites located on a separate domain of approximately 138 residues positioned at the C terminus of the alpha-macroglobulin subunit.

RESULTS

The crystal structure of the receptor-binding domain of bovine alpha 2-macroglobulin (bRBD) has been determined at a resolution of 1.9 A. The domain primarily comprises a nine-strand beta structure with a jelly-roll topology, but also contains two small alpha helices.

CONCLUSIONS

The surface patch responsible for receptor recognition is thought to involve residues located on one of the two alpha helices of the bRBD as well as residues in two of the beta strands. Located on this alpha helix are two lysine residues that are important for receptor binding. The structure of bRBD is very similar to the approximately 100-residue C-terminal domain of factor XIII, a transglutaminase from the blood coagulation system.

Native conformations of human complement components C3 and C4 show different dependencies on thioester formation

The thioester bond in complement components C3 and C4 and the protease inhibitor alpha2-macroglobulin have traditionally been thought of as fulfilling the dual roles of mediating covalent attachment and maintaining the native conformational states of these molecules. We previously reported that several human C3 thioester-region mutants, including variants E1012Q and C1010A, in the latter of which thioester-bond formation is precluded, display an unexpected phenotype. Despite the lack of a thioester bond in these mutants, they appear to adopt a native-like conformation as suggested by the finding that they are cleavable by the classical pathway C3 convertase, C4b2a, whereas the C3b-like C3(H2O) species is not. Subsequently, a species referred to as C3(NH3)* was described which potentially could account for the observations with the above mutants. C3(NH3)* is a transient species formed on aminolysis of native C3 that can spontaneously re-form the thioester bond. Importantly, it has a mobility on cation-exchange HPLC that is distinct from both native C3 and C3(H2O), but like the native molecule, it is cleavable by an alternative-pathway C3 convertase. In this study we showed by using cation-exchange HPLC as an additional conformational probe that C3 C1010A and E1012Q mutant proteins did not resemble C3(NH3)*. Instead they displayed a chromatographic behaviour that was indistinguishable from that of native C3. To assess the general applicability of these observations, we engineered the equivalent mutations into human C4, specifically C4 C1010A and C4 E1012Q. As expected, thioester-bond formation did not occur in either of these C4 mutants, but in contrast with the results with C3 we found no evidence for the formation of a stable native-like conformation in either C4 mutant, as assessed using cleavability by C1s as the conformational probe. A possible interpretation of our data is that the adoption of the native conformational state during biosynthesis of C3 and C4 is an energetically permissible process, even if it is not locked in via thioester-bond formation. Whereas this conformational state is stable in mature C3, it is unstable in mature C4, perhaps reflecting the additional post-translational cleavage of C4 before its secretion.

Identification of residues in alpha-macroglobulins important for binding to the alpha2-macroglobulin receptor/Low density lipoprotein receptor-related protein

Variants of the receptor binding domain of both human alpha2-macroglobulin and the corresponding domain of hen egg white ovomacroglobulin have been expressed in Escherichia coli and refolded in vitro. Competition experiments with methylamine-treated alpha2-macroglobulin for binding to the multifunctional alpha2-macroglobulin receptor identify two Lys residues (residues 1370 and 1374 in human alpha2-macroglobulin) spaced by three amino acid residues as crucial for receptor binding. From this result and mutational evidence from other ligands for the alpha2-macroglobulin receptor, a tentative sequence motif for receptor binding is proposed.

Human matrix metalloproteinase specificity studies using collagen sequence-based synthetic peptides

The matrix metalloproteinase (MMP)/matrixin family has been implicated in both normal tissue remodeling and a variety of diseases associated with abnormal turnover of extracellular matrix components. To better understand MMP behaviors and to aid in the design of MMP inhibitors, a variety of sequence specificity studies have been performed using collagen sequence-based peptides and MMP family members. Results of these studies have been valuable for defining the differences in MMPs and for creating fluorogenic substrates that can continuously monitor MMP activity. However, these studies have also demonstrated that these peptides may not be very good models of native MMP substrates, and that the additivity principle is not always applicable for designing synthetic MMP substrates.