Biomedical subjects

J O Sunyer

Publications and source records attributed to J O Sunyer.

11 recordsLinked to original sources

PubMed1998

Cloning, structure, and function of two rainbow trout Bf molecules.

The factor B (Bf) and C2 complement genes are closely linked within the MHC class III region and are thought to have arisen by gene duplication from a single gene encoding an ancestral molecule; the animal phyla in which this duplication event took place is unknown. Two teleost fish, (zebrafish and medaka fish) have each been shown to possess only a single molecule that shows an equivalent degree of similarity to mammalian Bf and C2. In contrast, here we present the characterization of two factor B molecules (Bf-1 and Bf-2) in another teleost fish (the rainbow trout) that are about 9% more similar to mammalian factor B than C2, yet play a role in both alternative and classical pathways of complement activation. The full lengths of Bf-1 and Bf-2 cDNAs are 2509 and 2560 bp, respectively, and their deduced amino acid sequences are 75% identical. Both trout Bf genes are mainly expressed in liver and appear to be single-copy genes. The isolated Bf-1 and Bf-2 proteins are able to form the alternative pathway C3 convertase and are cleaved (in the presence of purified trout C3, trout factor D, and Mg2+ EGTA) into Ba- and Bb-like fragments in a manner similar to that seen for mammalian factor B. The most remarkable feature of trout Bf-2 is its ability to restore the hemolytic activity of trout Bf-depleted serum through both the alternative and classical pathways; whether Bf-1 possess similar activity is unclear at present.

Amino Acid Sequence↗

PubMed1998

Sea urchin coelomocytes specifically express a homologue of the complement component C3.

A homologue of complement component C3 (SpC3) has been cloned and sequenced from the purple sea urchin, Strongylocentrotus purpuratus. The preprocessed, deduced protein size is estimated to be 186 kDa with a short leader and two chains, alpha and beta. There are cysteines in conserved positions for interchain disulfide bonding, and there is a conserved thioester site in the alpha-chain with an associated histidine. There are five consensus N-linked glycosylation sites, and putative cleavage sites for factor I and C3 convertase. Partially purified SpC3 on protein gels shows a nonreduced size of 210 kDa and, under reducing conditions, reveals an alpha-chain of 130 kDa and a beta-chain of 80 kDa. These sizes are larger than the deduced sizes, suggesting that the protein has carbohydrates added to most of the consensus N-linked glycosylation sites. Phylogenetic analysis of SpC3 compared with other members of the thioester protein family, which includes C3, C4, C5, and alpha2-macroglobulin, shows that SpC3 is the first divergent complement protein, falling at the base of the complement protein clade. Transcripts from the SpC3 gene (Sp064) are 9 kb, and the gene is expressed specifically in coelomocytes, which are the immunocytes in the sea urchin. Genome blots suggest that SpC3 is encoded by a single copy gene per haploid genome. This is the first identification of a complement component in an invertebrate, and suggests homology of the innate immune system within the deuterostome lineage of animals.

Amino Acid Sequence↗

PubMed1998

Structure, functions, and evolution of the third complement component and viral molecular mimicry.

The third component of the complement system, C3, is a common denominator in the activation of the classical, alternative, and lectin pathways. The ability of C3 molecule to interact with at least 20 different proteins makes it the most versatile component of this system. Since these interactions are important for phagocytic, immunoregulatory, and immune evasion mechanisms, the analysis of its structure and functions has been a subject of intense research. Here we review our current work on the C3-ligand interactions, C3-related viral molecular mimicry, evolution of the complement system, and identification of C3-based complement inhibitors.

Animals↗

PubMed1998

Complement diversity: a mechanism for generating immune diversity?

Unlike mammalian species, several cold-blooded species have been shown to possess multiple forms of complement components. The multiple forms of C3 characterized in several fish species can bind with different specificities to various complement-activating surfaces. Here, Oriol Sunyer, Ioannis Zarkadis and John Lambris explore the possible advantages conferred by having multiple forms of individual complement proteins in a single organism.

Animals↗

PubMed1998

Evolution and diversity of the complement system of poikilothermic vertebrates.

In mammals the complement system plays an important role in innate and acquired host defense mechanisms against infection and in various immunoregulatory processes. The complement system is an ancient defense mechanism that is already present in the invertebrate deuterostomes. In these species as well as in agnathans (the most primitive vertebrate species), both the alternative and lectin pathway of complement activation are already present, and the complement system appears to be involved mainly in opsonization of foreign material. With the emergence of immunoglobulins in cartilaginous fish, the classical and lytic pathways first appear. The rest of the poikilothermic species, from teleosts to reptilians, appear to contain a well-developed complement system resembling that of homeothermic vertebrates. However, important differences remain. Unlike homeotherms, several species of poikilotherms have recently been shown to possess multiple forms of complement components (C3 and factor B) that are structurally and functionally more diverse than those of higher vertebrates. It is noteworthy that the multiple forms of C3 that have been characterized in several teleost fish are able to bind with varying efficiencies to various complement-activating surfaces. We hypothesize that this diversity has allowed these animals to expand their innate capacity for immune recognition.

Animals↗

PubMed1997

Diversity of the third form of complement, C3, in fish: functional characterization of five forms of C3 in the diploid fish Sparus aurata.

We have recently shown that Sparus aurata, the gilthead sea bream (a diploid species), similarly to rainbow trout (a quasi-tetraploid species), possesses multiple forms of the third form of complement (C3). In the present study we have evaluated the ability of the gilthead sea bream proteins to function as active C3 molecules. All five C3 isoforms could be fixed covalently to sheep erythrocyte ghosts and were able to bind to various complement-activating surfaces in the presence of MgEGTA. In the absence of MgEGTA their binding capacities generally increased, presumably as a result of classical-pathway activation by the natural antibodies present in the serum. The presence of EDTA abrogated the binding of all C3 isoforms to the various surfaces tested. The C3 isoforms differed in the efficiency of their binding to complement-activating surfaces: the two most abundant C3 isoforms (C3-1 and C3-2) bound to zymosan as well as to sheep and rabbit erythrocyte ghosts, whereas C3-3, C3-4 and C3-5 were unable to bind to zymosan. Upon complement activation, all five C3 isoforms were cleaved to 'iC3b' by factor H and I-like proteins, generating fragments similar to those generated from C3 molecules of other species. Furthermore the degradation of methylamine-hydrolysed C3 isoforms to iC3b was significantly inhibited by EDTA. The structural and functional diversity that we have observed in the C3 isoforms of S. aurata would increase the capacity of this fish to recognize a broader spectrum of potential pathogens and reinforce a specific immune response, which in fish is delayed compared with that of higher vertebrates, and is based on a single Ig type (IgM).

Animals↗

PubMed1997

Structural C3 diversity in fish: characterization of five forms of C3 in the diploid fish Sparus aurata.

In virtually all species examined to date, the functionally active third component of complement (C3) is encoded by a single gene. We have recently demonstrated, however, that trout possess three structurally and functionally distinct active C3 that represent the products of at least two different C3 genes. In the present study, we provide evidence that multiple forms of functional C3 occur not only in the rainbow trout (Salmo gairdneri), a quasi-tetraploid old teleost fish, but also in the diploid gilthead sea bream (Sparus aurata), a modern teleost fish. In the gilthead sea bream, we have characterized five different forms of C3 (C3-1, C3-2, C3-3, C3-4, and C3-5); in addition, we have identified and isolated a C5-like molecule. Each of the six proteins was composed of an alpha-chain and a beta-chain; however, only the C3 isoforms contained a thioester bond in their alpha-chains. These proteins all differed in the molecular masses of their alpha- and beta-chains and in their glycosylation patterns, reactivity with various Abs, tryptic peptide maps, and NH2-terminal sequences of their chains. These observations together with the fact that each of the six proteins were also purified from a single fish suggest that the C3 isoforms represent the products of several genes. The presence of multiple forms of C3 in a modern diploid fish, very distant in evolutionary time from the trout, strongly suggests that the C3 isoforms generated once from a single C3 gene have remained functional in the genomes of these animals. These findings not only have important consequences for our understanding of the evolution of the C3 protein, but also provide evidence for the formation and generation of a new C3-related gene family.

Amino Acid Sequence↗

PubMed1996

Multiple forms of complement C3 in trout that differ in binding to complement activators.

In all other species analyzed to date, the functionally active form of complement component C3 exists as the product of a single gene. We have now identified and characterized three functional C3 proteins (C3-1, C3-3, and C3-4) in trout that are the products of at least two distinct C3 genes. All three proteins are composed of an alpha-and a beta-chain and contain a thioester bond in the alpha-chain. However, they differ in their electrophoretic mobility, glycosylation, reactivity with monospecific C3 antibodies, and relative ability to bind to various surfaces (zymosan, Escherichia coli, erythrocytes). A comparison of the partial amino acid sequences of the three proteins showed that the amino acid sequence identity/similarity of C3-3 to C3-4 is 87/91%, while that of C3-3 and C3-4 to C3-1 is 51.5/65.5% and 60/73% respectively. Thus, trout possess multiple forms of functional C3 that represent the products of several distinct genes and differ in their ability to bind covalently to various complement activators.

Amino Acid Sequence↗

PubMed1996

Crowding stress induces changes in serum haemolytic and agglutinating activity in the gilthead sea bream Sparus aurata.

Sea bream Sparus aurata were subjected to crowding for 3 weeks and the levels of plasma cortisol and glucose were determined in order to ascertain the occurrence of stress. At the same time, selected indicators of the immune response were monitored through blood lymphocyte counting and selected humoral responses such as the haemagglutination activity (HA) of serum towards rabbit erythrocytes (RaRBC) and the alternative complement pathway (ACP) levels. The results show an initial moderate increase in cortisol followed by hyperglycaemia and recovery to basal levels. A pattern of immunodepression was detected afterwards as shown by decreases in ACP levels after 5 days and haemagglutination titre and circulating lymphocytes after 9 days. Nevertheless, ACP levels showed a significant increase after 9 days, and HA titres and circulating lymphocyte numbers also increased after 15 days. Normal values were recovered after 15 days for lymphocytes and ACP and 21 days for agglutination. Results are discussed in view of the incidence of stress on indicative parameters of endocrine and immune systems.

Agglutination↗

PubMed1995

Isolation, primary structure, and evolution of the third component of chicken complement and evidence for a new member of the alpha 2-macroglobulin family.

Although the third component of complement, C3, has been isolated and its primary structure determined from most living classes of vertebrate, limited information is available on its structure and function for aves, which represent a significant stage in complement evolution. In this study, we present the complete cDNA sequence of chicken C3, the cDNA sequences of the thioester region for two chicken alpha 2-macroglobulin (alpha 2M)-related proteins, a simplified method for purifying chicken C3, and an analysis of the C3 convertase and factor I-mediated cleavages in chicken C3. Using the reverse-transcriptase PCR, with degenerate oligonucleotide primers derived from two conserved C3 sequences (GCGEQN/TM, TWLTAY/FV) and liver mRNA as template, we isolated three distinct 220-bp PCR products, one with a high degree of sequence similarity to C3 and two to alpha 2M and pregnancy zone protein from other species. The complete cDNA sequence of chicken C3 was obtained by screening a chicken liver lambda gt10 library with the C3 PCR product and probes from the 5' end of the partial-length C3 clones. The obtained sequence is in complete agreement with the protein sequence of several tryptic peptides of purified chicken C3. Chicken pro-C3 consists of an 18-residue putative signal peptide, a 640-residue beta-chain (70 kDa), a 989-residue alpha-chain (111 kDa), and an RKRR linker region. It contains an internal thioester and three potential N-glycosylation sites, all in the alpha-chain. The convertase cleavage site, predicted to be Arg-Ser, was confirmed by sequencing the zymosan-bound C3 fragments generated upon complement activation. NH2-terminal sequencing of the purified C3 chains showed that 1) pro-C3 is indeed cleaved at the RKRR linker sequence to generate the mature two-chain molecule, and 2) the beta-chain of chicken C3 is blocked. The deduced amino acid sequence shows 54, 54, 54, 53, 52, 57, and 55% amino acid identities to human, mouse, rat, guinea pig, rabbit, cobra, and Xenopus C3, respectively, and an identity of 44, 31, and 33% to trout, hagfish, and lamprey C3, respectively. The identities to human C4, C5, and alpha 2M are 31, 29 and 23%, respectively. A phylogenetic tree for C3, C4, C5, and alpha 2M-related proteins was constructed based on the sequence data and is discussed.

Amino Acid Sequence↗

PubMed1995

Natural hemolytic and bactericidal activities of sea bream Sparus aurata serum are effected by the alternative complement pathway.

Sea bream serum displayed bactericidal and hemolytic activities. These activities were depleted when serum was incubated with different activators of the alternative complement pathway (ACP). Ethylenediaminetetraacetic acid (EDTA) inhibited both the hemolytic and bactericidal activities, while ethyleneglycol-bis (B-aminoethyl ether)-N, N, N'-tetraacetic acid (EGTA) was not inhibitory. An antibody against the putative third component of sea bream component (C3) was produced. It was observed by immunoelectrophoresis that the sea bream C3 and human C3 migrated in the same position. Crossed immunoelectrophoresis showed that sea bream C3 exhibited a similar pattern of activation when compared with its human counterpart. The anti-sea bream C3 antibody inhibited both bactericidal and hemolytic activities. It was concluded that both serum actions were displayed by the ACP. The best conditions for the sea bream ACP titration were investigated. Of all mammal erythrocytes tested, rabbit erythrocytes (RaRBC) were found to be the best ACP activators and thus were used for the titration. Sea bream showed very high ACP titers when compared with those of mammals. Absorption of naturally occurring antibodies against rabbit RaRBC did not influence the ACP titers. Enzymatic removal of sialic acid from different mammalian erythrocytes increased the sensitivity of these cells to hemolysis mediated by the sea bream ACP.

Animals↗