Accelerated evolution in inhibitor domains of porcine elafin family members

Kunitzins: Prototypes of a new class of protease inhibitor from the skin secretions of European and Asian frogs

Amphibian skin secretions contain biologically-active compounds, such as anti-microbial peptides and trypsin inhibitors, which are used by biomedical researchers as a source of potential novel drug leads or pharmacological agents. Here, we report the application of a recently developed technique within our laboratory to "shotgun" clone the cDNAs encoding two novel but structurally-related peptides from the lyophilised skin secretions of one species of European frog, Rana esculenta and one species of Chinese frog, Odorrana schmackeri. Bioanalysis of the peptides established the structure of a 17-mer with an N-terminal Ala (A) residue and a C-terminal Cys (C) residue with a single disulphide bridge between Cys 12 and 17, which is a canonical Kunitz-type protease inhibitor motif (-CKAAFC-). Due to the presence of this structural attribute, these peptides were named kunitzin-RE (AAKIILNPKFRCKAAFC) and kunitzin-OS (AVNIPFKVHLRCKAAFC). Synthetic replicates of these two novel peptides were found to display a potent inhibitory activity against Escherichia coli but were ineffective at inhibiting the growth of Staphylococcus aureus and Candida albicans at concentrations up to 160 μM, and both showed little haemolytic activity at concentrations up to 120 μM. Subsequently, kunitzin-RE and kunitzin-OS were found to be a potent inhibitor of trypsin with a Ki of 5.56 μM and 7.56 μM that represent prototypes of a novel class of highly-attenuated amphibian skin protease inhibitor. Substitution of Lys-13, the predicted residue occupying the P1 position within the inhibitory loop, with Phe (F) resulted in decrease in trypsin inhibitor effectiveness and antimicrobial activity against Esherichia coli, but exhibits a potential inhibition activity against chymotrypsin.

Chemical specificity and conformational flexibility in proteinase-inhibitor interaction: scaffolds for promiscuous binding

One of the most important roles of proteins in cellular milieu is recognition of other biomolecules including other proteins. Protein-protein complexes are involved in many essential cellular processes. Interfaces of protein-protein complexes are traditionally known to be conserved in evolution and less flexible than other solvent interacting tertiary structural surface. But many examples are emerging where these features do not hold good. An understanding of inter-play between flexibility and sequence conservation is emerging, providing a fresh dimension to the paradigm of sequence-structure-function relationship. The functional manifestation of the inter-relation between sequence conservation and flexibility of interface is exemplified in this review using proteinase-inhibitor protein complexes.

Differences in gene organization between type I and type II crustins in the morotoge shrimp, Pandalopsis japonica

Crustins are cysteine-rich cationic antimicrobial peptides (AMPs) found in decapod crustaceans. Six novel crustin genes (Paj-CrusIc, Id, Ie, If, IIb and IIc) were identified in the morotoge shrimp, Pandalopsis japonica. Deduced amino acid sequences of isolated Paj-Crus genes ranged from 99 to 178 amino acid residues (10.6-17.8 kDa). Sequence analysis of nine isolated Paj-Crus genes and 100 different crustins from various decapod crustaceans revealed that a splice site and KXXXCP motif within the WAP domain may be the main criteria for classifying type I and II crustins, suggesting that the two types of crustin genes may have been generated by different processes. We also identified three intron-less crustin I genes (Paj-Crus Id, Ie and If) for the first time, which may have been generated by gene duplication. The tissue distribution profiles showed that Paj-CrusI genes were expressed predominantly in the gill and epidermis, whereas Paj-CrusII genes were expressed ubiquitously, suggesting that the two types of crustins may play different roles in various tissues or under different physiological conditions. Differing from previous results, hemocyte-specific crustin was not isolated from Pandalopsis japonica. This study showed that both types of crustin genes (types I and II) exist in decapod crustaceans and their primary structure and expression profiles differ from each other, suggesting that they may play different biological roles. This will help to extend our knowledge of the crustacean innate immune response, which will provide important basic information of shrimp immunity against various pathogens.

Evolution of trappin genes in mammals

Background

Trappin is a multifunctional host-defense peptide that has antiproteolytic, antiinflammatory, and antimicrobial activities. The numbers and compositions of trappin paralogs vary among mammalian species: human and sheep have a single trappin-2 gene; mouse and rat have no trappin gene; pig and cow have multiple trappin genes; and guinea pig has a trappin gene and two other derivativegenes. Independent duplications of trappin genes in pig and cow were observed recently after the species were separated. To determine whether these trappin gene duplications are restricted only to certain mammalian lineages, we analyzed recently-developed genome databases for the presence of duplicate trappin genes.

Results

The database analyses revealed that: 1) duplicated trappin multigenes were found recently in the nine-banded armadillo; 2) duplicated two trappin genes had been found in the Afrotherian species (elephant, tenrec, and hyrax) since ancient days; 3) a single trappin-2 gene was found in various eutherians species; and 4) no typical trappin gene has been found in chicken, zebra finch, and opossum. Bayesian analysis estimated the date of the duplication of trappin genes in the Afrotheria, guinea pig, armadillo, cow, and pig to be 244, 35, 11, 13, and 3 million-years ago, respectively. The coding regions of trappin multigenes of almadillo, bovine, and pig evolved much faster than the noncoding exons, introns, and the flanking regions, showing that these genes have undergone accelerated evolution, and positive Darwinian selection was observed in pig-specific trappin paralogs.

Conclusion

These results suggest that trappin is an eutherian-specific molecule and eutherian genomes have the potential to form trappin multigenes.

HV-BBI--a novel amphibian skin Bowman-Birk-like trypsin inhibitor

Here we describe the isolation of a novel C-terminally amidated octadecapeptide--SVIGCWTKSIPPRPCFVK-amide--that contains a disulphide loop between Cys(5) and Cys(15) that is consistent with a Bowman-Birk type protease inhibitor, from the skin secretion of the Chinese Bamboo odorous frog, Huia versabilis. Named HV-BBI, the peptide is encoded by a single precursor of 62 amino acid residues whose primary structure was deduced from cloned skin cDNA. The precursor exhibits the typical organization of that encoding an amphibian skin peptide with a highly-conserved signal peptide, an intervening acidic amino acid residue-rich domain and a single HV-BBI-encoding domain located towards the C-terminus. A synthetic replicate of HV-BBI, with the wild-type K (Lys-8) residue in the presumed P1 position, was found to be a potent inhibitor of trypsin with a K(i) just slightly less than 19 nM. Substitution at this site with R (Arg) resulted in a significant reduction in potency (K(i) 57 nM), whereas replacement of K with F (Phe) resulted in the complete abolition of trypsin inhibitory activity. Thus, HV-BBI is a potent inhibitor of trypsin and the lysyl (K) residue that occupies the P1 position appears to be optimal for potency of action against this protease.

Reduction of tumorigenesis and invasion of human breast cancer cells by whey acidic protein (WAP)

Whey acidic protein (WAP) is a major component of whey, which has two or three WAP motif domains characterized by a four-disulfide core (4-DSC) structure similar to the serine protease inhibitor. We have previously found that WAP inhibits the proliferation of mammary epithelial cells in vitro and in vivo [N. Nukumi, K. Ikeda, M. Osawa, T. Iwamori, K. Naito, H. Tojo, Regulatory function of whey acidic protein in the proliferation of mouse mammary epithelial cells in vivo and in vitro, Dev. Biol. 274 (2004) 31-44]. We report herein that WAP also reduces the progression of human breast cancer cells (MCF-7 and MDA-MB-453 cells). We have demonstrated that the forced expression of WAP in MCF-7 cells reduces the proliferation in either the presence or absence of estrogen. The tumor progression of WAP-expressing MCF-7 cells in nude mice is significantly suppressed more than that of mock-MCF-7 cells following the reduced expression of angiopoietin-2 gene. We have confirmed that the invasive activity of breast cancer cells is reduced to approximately 30% of that of mock cells by the forced expression of exogenous WAP through its inhibition of degradation of laminin. These data suggest that WAP has a protease-inhibitory function on the progression of breast cancer cells. It is therefore possible to utilize WAP as therapeutic protein against tumorigenesis of breast cancer.

SLPI and elafin: one glove, many fingers

Elafin and SLPI (secretory leucocyte protease inhibitor) have multiple important roles both in normal homoeostasis and at sites of inflammation. These include antiprotease and antimicrobial activity as well as modulation of the response to LPS (lipopolysaccharide) stimulation. Elafin and SLPI are members of larger families of proteins secreted predominantly at mucosal sites, and have been shown to be modulated in multiple pathological conditions. We believe that elafin and SLPI are important molecules in the controlled functioning of the innate immune system, and may have further importance in the integration of this system with the adaptive immune response. Recent interest has focused on the influence of inflamed tissues on the recruitment and phenotypic modulation of cells of the adaptive immune system and, indeed, the local production of elafin and SLPI indicate that they are ideally placed in this regard. Functionally related proteins, such as the defensins and cathelicidins, have been shown to have direct effects upon dendritic cells with potential alteration of their phenotype towards type I or II immune responses. This review addresses the multiple functions of elafin and SLPI in the inflammatory response and discusses further their roles in the development of the adaptive immune response.

Elafin and its precursor trappin-2 still inhibit neutrophil serine proteinases when they are covalently bound to extracellular matrix proteins by tissue transglutaminase

Elafin and its precursor trappin-2 (also called pre-elafin) are potent protein inhibitors of neutrophil serine proteases such as leukocyte elastase and proteinase 3. Trappin-2 has unique conserved sequence motifs rich in Gln and Lys residues. These motifs are substrates for transglutaminases that may enable trappin-2 to be cross-linked to extracellular matrix proteins, thus anchoring the inhibitor at its site of action. We have used Western blotting and ELISA-based assays to demonstrate that both elafin and trappin-2 can be conjugated to various extracellular matrix proteins in vitro by a type 2 transglutaminase. Cross-linked elafin and trappin-2 still inhibited their target proteases. Surface plasmon resonance studies allowed the determination of the kinetic constants governing the interaction of fibronectin-bound elafin and trappin-2 with neutrophil elastase and proteinase 3. Both inhibitors were potent inhibitors when cross-linked to fibronectin by transglutamination, with equilibrium dissociation constants K(i) for their interaction with target proteases of 0.3 nM (elastase-elafin), 20 nM (proteinase 3-elafin), 0.3 nM (elastase-trappin-2), and 12 nM (proteinase 3-trappin-2). The conjugated inhibitors reacted more slowly with their target enzymes than did the soluble inhibitors, perhaps due to their immobilization, with association rate constants of 2-7 x 10(5) M(-)(1) s(-)(1) for elastase and 1-4 x 10(4) M(-)(1) s(-)(1) for proteinase 3. We believe this is the first demonstration that transglutaminase-mediated cross-linking of serine protease inhibitors to proteins preserves their inhibitory capacities.

Identification, evolution, and regulation of expression of Guinea pig trappin with an unusually long transglutaminase substrate domain

Trappins are found in human, bovine, hippopotamus, and members of the pig family, but not in rat and mouse. To clarify the evolution of the trappin genes and the functional significance of their products, we isolated the trappin gene in guinea pig, a species belonging to a rodent family distinct from rat and mouse. Guinea pig trappin was confirmed to encode the same domain structure as trappin, consisting of a signal sequence, an extra large transglutaminase substrate domain, and a whey acidic protein motif. Northern blot analysis and in situ hybridization histochemistry as well as immunohistochemistry demonstrated that guinea pig trappin is expressed solely in the secretory epithelium of the seminal vesicle and that its expression is androgen-dependent. We confirmed that guinea pig trappin is cross-linked by prostate transglutaminase and that the whey acidic protein motif derived from guinea pig trappin has an inhibitory activity against leukocyte elastase. Genome sequence analysis showed that guinea pig trappin belongs to the family of REST (rapidly evolving seminal vesicle transcribed) genes.

Androgen-Dependent Expression, Gene Structure, and Molecular Evolution of Guinea Pig Caltrin II, a WAP-Motif Protein1

We determined the cDNA and gene structures of guinea pig caltrin II, a unique member of the calcium transporter inhibitors containing a whey acidic protein (WAP) motif, and we established that it is a secretory protein with a potential 21-amino acid signal peptide in its N-terminus. Northern blot analysis and in situ hybridization histochemistry indicated that the expression of caltrin II is restricted to luminal epithelial cells in the seminal vesicles. Its message levels markedly decreased either after castration (and were restored by simultaneous administration of testosterone) or after treatment of the animals with estradiol, suggesting that the expression of caltrin II is androgen-dependent. Recombinant caltrin II had an elastase-inhibitor activity. Comparison of sequence between the caltrin II and related genes and their molecular evolutionary analyses revealed that caltrin II and seminal vesicle secretory proteins (SVPs) appear to be evolved from a common ancestor gene that is made by the fusion of semenogelin and trappin genes. Caltrin II and SVPs lost the transglutaminase substrate domain and the WAP motif, respectively, within a single exon, resulting in the exertion of different functions.

Identification of crotasin, a crotamine-related gene of Crotalus durissus terrificus

Crotamine is a cationic peptide (4.9 kDa, pI 9.5) of South American rattlesnake, Crotalus durissus terrificus' venom. Its presence varies according to the subspecies or the geographical locality of a given species. At the genomic level, we observed the presence of 1.8 kb gene, Crt-p1, in crotamine-positive specimens and its absence in crotamine-negative ones. In this work, we described a crotamine-related 2.5 kb gene, crotasin (Cts-p2), isolated from crotamine-negative specimens. Reverse transcription coupled to polymerase chain reaction indicates that Cts-p2 is abundantly expressed in several snake tissues, but scarcely expressed in the venom gland. The genome of crotamine-positive specimen contains both Crt-p1 and Cts-p2 genes. The present data suggest that both crotamine and crotasin have evolved by duplication of a common ancestor gene, and the conservation of their three disulfide bonds indicates that they might adopt the same fold as beta-defensin. The physiological function of the crotasin is not yet known.

Trappin ovine molecule (TOM), the ovine ortholog of elafin, is an acute phase reactant in the lung

As large animal models continue to play an important role in translating lung-directed therapeutic strategies from laboratory animals to humans, there is an increasing interest in the analysis of endogenous regulators of inflammation at both a genomic and a therapeutic level. To this end, we have sought to characterize the ovine ortholog of elafin, an important regulator of inflammation in humans. We have isolated both the elafin cDNA and gene, which have a similar structure to other species' orthologs. Interestingly, we have isolated two alleles for ovine elafin, which contain a very high number of transglutamination repeats, thought to be important in binding elafin to the interstitium. The mainly mucosal mRNA distribution for ovine elafin suggests that ovine elafin may, like its human ortholog, have functions in innate immunity. This is supported by analysis of elafin and the related protein secretory leukocyte protease inhibitor (SLPI) in ovine bronchoalveolar fluid in response to locally administered lipopolysaccharide and confirmation of them acting as "alarm" antiproteases. We have also cloned the ovine elafin cDNA into an adenoviral vector and have demonstrated correct processing of the secreted protein as well as biological activity. Overexpression of ovine elafin in a lung-derived epithelial cell line has a protective effect against the enzymes human neutrophil and porcine pancreatic elastase. The identification of the ovine elafin gene and its translated protein are important in developing practical strategies aimed at regulating inflammation in the large mammalian lung.

Identification of a novel family of proteins in snake venoms. Purification and structural characterization of nawaprin from Naja nigricollis snake venom

The three-dimensional structure of nawaprin has been determined by nuclear magnetic resonance spectroscopy. This 51-amino acid residue peptide was isolated from the venom of the spitting cobra, Naja nigricollis, and is the first member of a new family of snake venom proteins referred to as waprins. Nawaprin is relatively flat and disc-like in shape, characterized by a spiral backbone configuration that forms outer and inner circular segments. The two circular segments are held together by four disulfide bonds, three of which are clustered at the base of the molecule. The inner segment contains a short antiparallel beta-sheet, whereas the outer segment is devoid of secondary structures except for a small turn or 310 helix. The structure of nawaprin is very similar to elafin, a human leukocyte elastase-specific inhibitor. Although substantial parts of the nawaprin molecule are well defined, the tips of the outer and inner circular segments, which are hypothesized to be critical for binding interactions, are apparently disordered, similar to that found in elafin. The amino acid residues in these important regions in nawaprin are different from those in elafin, suggesting that nawaprin is not an elastase-specific inhibitor and therefore has a different function in the snake venom.

Identification and molecular cloning of novel trypsin inhibitor analogs from the dermal venom of the Oriental fire-bellied toad (Bombina orientalis) and the European yellow-bellied toad (Bombina variegata)

The structural diversity of polypeptides in amphibian skin secretion probably reflects different roles in dermal regulation or in defense against predators. Here we report the structures of two novel trypsin inhibitor analogs, BOTI and BVTI, from the dermal venom of the toads, Bombina orientalis and Bombina variegata. Cloning of their respective precursors was achieved from lyophilized venom cDNA libraries for the first time. Amino acid alignment revealed that both deduced peptides, consisting of 60 amino acid residues, including 10 cysteines and the reactive center motif, -CDKKC-, can be affirmed as structural homologs of the trypsin inhibitor from Bombina bombina skin.

Three related TrIV genes: comparative sequence analysis and expression in host larvae and Cf-124T cells

We report on the cloning and sequencing of two Tranosema rostrale ichnovirus (TrIV) genes, and assess their relatedness to TrV1, the gene encoding the most abundant TrIV transcript in last-instar Choristoneura fumiferana larvae parasitized by T. rostrale. One of the two newly isolated genes, TrV2, features an organization similar to that of TrV1, with one intron flanked by two exons; it encodes a 102 amino acid protein showing 79% similarity to TrV1. The third gene, TrV4, encodes a larger protein (143 aa) displaying similarity to the other two only over the first approximately 50 amino acid residues of its sequence; the remaining portion contains an imperfect octad repeat. Although the TrV4 gene contains only one exon, it has an intron similar in size and sequence to that of TrV1 and TrV2; in fact, the non-coding regions of all three genes show higher sequence identity than the coding regions, pointing to their common origin. Southern analysis suggests that each gene maps to a different TrIV genome segment, with homologous sequences apparently present on other segments. TrV1 and TrV4 transcription in penultimate (5th) instar hosts, parasitized shortly after the molt, was strong for both genes 1 and 2 days p.p., with transcript abundance decreasing after the final molt; thus, neither of these genes is upregulated during induction of developmental arrest in last-instar hosts. Cf-124T cells inoculated with T. rostrale calyx fluid showed significant levels of apoptosis 24-72 h p.i.; TrV1 was detected in the culture medium, suggesting that this and/or other TrIV-encoded proteins may be responsible for the observed cytopathic effect. Southern and Northern analyses, using DNA and RNA extracted from infected Cf-124T cells, revealed the presence of both TrV1- and TrV4-carrying genome segments and transcripts, but neither DNA, at least in episomal form, nor mRNA persisted for more than a few days p.i. This in vitro system may provide a suitable starting point for the study of TrIV gene functions.

Mouse SWAM1 and SWAM2 are antibacterial proteins composed of a single whey acidic protein motif

Antibacterial proteins are important participants in the innate immunity system. Elafin and SLPI are the whey acidic protein (WAP) motif proteins with both antibacterial activity and antiprotease activity, and their role in innate immunity is under intense investigation. We cloned two novel antibacterial WAP motif proteins from mice, SWAM1 and SWAM2. SWAM1 and SWAM2 are composed of a signal sequence and a single WAP motif that has high homologies with the WAP motifs of elafin and SLPI. SWAM1 is constitutively expressed in kidney and epididymis, and is induced in the pneumonic lung. SWAM2 is constitutively expressed in tongue. SWAM1 and SWAM2 inhibit the growth of both Escherichia coli and Staphylococcus aureus at a IC(90) (concentration that achieves 90% inhibition) of 10 microM. Human genes LOC149709 and huWAP2 are considered to be human SWAM1 and SWAM2, respectively. These and several WAP motif proteins (WAP1, elafin, SLPI, HE4, eppin, C20orf170, LOC164237, and WFDC3) form a gene cluster on human chromosome 20, suggesting that they may be derived from the same ancestral gene by gene duplication. Our results underscore the role of the WAP motif as a skeletal motif to form antibacterial proteins, and warrant the study of antibacterial activity in other WAP motif proteins.

Antimicrobial peptides and protease inhibitors in the skin secretions of the crawfish frog, Rana areolata

The dorsal skin of the crawfish frog, Rana areolata, is associated with numerous prominent granular glands. Proteomic analysis of electrically stimulated skin secretions from these glands enabled the identification and characterization of eight peptides with antimicrobial and hemolytic activity belonging to the previously identified brevinin-1, temporin-1, palustrin-2, palustrin-3, esculentin-1 (two peptides), and ranatuerin-2 (two peptides) families. The primary structures of the peptides were consistent with a close phylogenetic relationship between R. areolata and the pickerel frog, Rana palustris. Three structurally related cationic, cysteine-containing peptides were identified that show sequence similarity to peptide Leucine-Arginine, a peptide with immunomodulatory and histamine-releasing properties from the skin of the northern leopard frog, Rana pipiens. The skin secretions contained a 61-amino-acid-residue peptide that inhibited porcine trypsin and possessed a 10-cysteine-residue motif that is characteristic of a protease inhibitor previously isolated from the parasitic nematode, Ascaris suum. A 48-amino-acid-residue protein containing eight cysteine residues in the whey acidic protein (WAP) motif, characteristic of elafin (skin-derived antileukoproteinase) and secretory leukocyte protease inhibitor, was also isolated. The data suggest that protease inhibitors in skin secretions may play a role complementary to cationic, amphipathic alpha-helical peptides in protecting anurans from invasions by microorganisms.

A locus on human chromosome 20 contains several genes expressing protease inhibitor domains with homology to whey acidic protein

A locus containing 14 genes, encoding protein domains that have homology with whey acidic protein (WAP), has been identified in a region of 678 kb on human chromosome 20q12-13.1. Among them are genes of the known or postulated protease inhibitors elafin, secretory leucocyte protease inhibitor, human epididymis gene product 4, eppin, and huWAP2. Nucleotide sequences of full-length transcripts were obtained from cDNA fragments generated by rapid amplification of cDNA ends. Characteristic features of the genes are that the upstream promoter regions are devoid of TATA-boxes and that the coding nucleotides are divided into distinct exons for the signal peptide and for each WAP domain. In most cases, there is also a separate exon encompassing a few terminal codons and the 3' untranslated nucleotides. There are also examples of mixed type inhibitors, that encode inhibitor domains of both WAP and Kunitz types. Several of the genes appear to be expressed ubiquitously, but, in most cases, the highest transcript levels are found in epididymis followed by testis and trachea. Some of the genes also display high transcript levels in neural tissues. Potential biological roles of protein products could be in host defence against invading micro-organisms or in the regulation of endogenous proteolytic enzymes, of which those originating from the kallikrein gene locus on chromosome 19 are of particular interest.

Multimeric hemoglobin of the Australian brine shrimp Parartemia

The hemoglobin molecule of the commercially important brine shrimp Artemia sp. has been used extensively as a model for the study of molecular evolution. It consists of nine globin domains joined by short linker sequences, and these domains are believed to have originated through a series of duplications from an original globin gene. In addition, in Artemia, two different polymers of hemoglobin, called C and T, are found which differ by 11.7% at the amino acid level and are believed to have diverged about 60 MYA. This provides a set of data of 18 globin domain sequences that have evolved in the same organism. The pattern of amino acid substitution between these two polymers is unusual, with pairs of equivalent domains displaying differences of up to 2.7-fold in total amino acid substitution. Such differences would reflect a similar range of molecular-clock rates in what appear to be duplicate, structurally equivalent domains. In order to provide a reference outgroup, we sequenced the cDNA for a nine-domain hemoglobin (P) from another genus of brine shrimp, Parartemia zietziana, which differs morphologically and ecologically from Artemia and is endemic to Australia. Parartemia produces only one hundredth the amount of hemoglobin that Artemia produces and does not upregulate production in response to low oxygen partial pressure. Comparison of the globin domains at the amino acid and DNA levels suggests that the Artemia globin T gene has accumulated substitutions differently from the Parartemia P and Artemia C globin genes. We discuss the questions of accelerated evolution after duplication and possible functions for the Parartemia globin.

The gene for a novel member of the whey acidic protein family encodes three four-disulfide core domains and is asynchronously expressed during lactation

Secretion of whey acidic protein (WAP) in milk throughout lactation has previously been reported for a limited number of species, including the mouse, rat, rabbit, camel, and pig. We report here the isolation of WAP from the milk of a marsupial, the tammar wallaby (Macropus eugenii). Tammar WAP (tWAP) was isolated by reverse-phase HPLC and migrates in SDS-polyacrylamide gel electrophoresis at 29.9 kDa. tWAP is the major whey protein, but in contrast to eutherians, secretion is asynchronous and occurs only from approximately days 130 through 240 of lactation. The full-length cDNA codes for a mature protein of 191 amino acids, which is comprised of three four-disulfide core domains, contrasting with the two four-disulfide core domain arrangement in all other known WAPs. A three-dimensional model for tWAP has been constructed and suggests that the three domains have little interaction and could function independently. Analysis of the amino acid sequence suggests the protein belongs to a family of protease inhibitors; however, the predicted active site of these domains is dissimilar to the confirmed active site for known protease inhibitors. This suggests that any putative protease ligand may be unique to either the mammary gland, milk, or gut of the pouch young. Examination of the endocrine regulation of the tWAP gene showed consistently that the gene is prolactin-responsive but that the endocrine requirements for induction and maintenance of tWAP gene expression are different during lactation.

cDNA cloning of bradykinin-potentiating peptides-C-type natriuretic peptide precursor, and characterization of the novel peptide Leu3-blomhotin from the venom of Agkistrodon blomhoffi

A cDNA clone, 1.8 kb long, was isolated from a venom gland cDNA library of Agkistrodon blomhoffi that encodes a large plurifunctional precursor composed of 263 amino-acid residues. Nucleotide sequence analysis of this clone revealed that sequences which code for blomhotin and a novel peptide Leu3-blomhotin are located in the N-terminal region of the precursor polypeptide, followed by four tandemly aligned sequences which code for three types of bradykinin-potentiating peptide. In the C-terminal region, the sequence for the C-type natriuretic peptide was located along with a preceding processing signal. The deduced amino-acid sequences for the four bradykinin-potentiating peptides coincided exactly with previously known sequences for potentiator B, potentiator C and potentiator E. The actual Leu3-blomhotin peptide was subsequently isolated from the venom of A. blomhoffi and characterized. Leu3-blomhotin possesses contractile activity in isolated rat stomach fundus smooth muscle in the same manner as blomhotin. Furthermore, it was shown that blomhotin and Leu3-blomhotin retained activity to inhibit the angiotensin-converting enzyme.

Purification and characterization of a cysteine-rich 11.5-kDa antibacterial protein from the granular haemocytes of the shore crab, Carcinus maenas

Extracts of the granular haemocytes of Carcinus maenas were subjected to ion-exchange chromatography and reverse-phase (RP)-HPLC to investigate the presence of an antibacterial protein of approximately 11 kDa. This protein was isolated, characterized and subjected to partial amino acid sequence analysis. It was found by mass spectrometry to have a molecular mass of 11 534 Da, to be cationic and hydrophobic and active only against marine Gram-positive bacteria. In addition its activity is stable after heating to 100 degrees C and is retained at concentrations as low as 10 microgram.mL-1. It has an unusual amino acid sequence, unlike any known antibacterial peptide described in the literature but bears a consensus disulphide domain signature, indicating that it might be a member of the four-disulphide core proteins. Partial cDNA sequence data has been obtained.

Targeted overexpression of elafin protects mice against cardiac dysfunction and mortality following viral myocarditis

Serine elastases degrade elastin, stimulate vascular smooth muscle cell migration and proliferation, and are associated with myocardial damage. To evaluate the impact of elastase inhibition on cardiovascular development and disease, transgenic mice were created in which the mouse preproendothelin-1 promoter was used to target elafin overexpression to the cardiovascular system. To distinguish the transgene from endogenous elafin, constructs were made incorporating a FLAG sequence; the COOH-terminus FLAG-tagged elafin construct produced a stable, functionally active gene product and was used to create transgenic mice. Consistent with endothelin expression, abundant elafin mRNA was observed in transgenic F1 embryos (embryonic day 13.5) and in adult transgenic mice heart, trachea, aorta, kidney, lung, and skin, but not in liver, spleen, and intestine. Functional activity of the transgene was confirmed by heightened myocardial elastase inhibitory activity. No tissue abnormalities were detected by light microscopy or elastin content. However, injection of 10 plaque-forming units (PFU) of encephalomyocarditis virus resulted in death within 11 days in 10 out of 12 nontransgenic mice compared with one out of nine transgenic littermates. This reduced mortality was associated with better cardiac function and less myocardial inflammatory damage. Thus, elafin expression may confer a protective advantage in myocarditis and other inflammatory diseases.

Isolation of a gene family that encodes the porin-like proteins from the human parasitic nematode Trichuris trichiura

The major E/S protein of Trichuris trichiura, the human whipworm, is a highly immunogenic 47-kDa protein that has a pore forming activity that is thought to be essential for the attachment of the worm to host mucosal epithelium. By gene analysis, we have demonstrated that this protein belongs to a multigene family, and we have obtained genomic and cDNA information for two of these genes. The encoded proteins are composed of tandem arrays of alternating 50- and 51-amino-acid domains within which the positioning of the cysteine residues is highly conserved. This structure resembles that of four disulphide core domain proteins, such as secretory leucocyte proteinase-1 (SLP-1), but the Trichuris protein family differs in being composed of multiple domains of this type (nine in TT50, 17 in TT95). An analysis of the relationship between the domains, and a comparison of the fine arrangement of the genes, suggests that TT95 has arisen relatively recently following duplication of the TT50 gene, which itself arose by duplication of a SLP-1-like ancestor.

Retrotransposable CR1-like elements in crotalinae snake genomes

A part of the 3'-flanking region of BP-II gene, which is one of Trimeresurus flavoviridis venom gland phospholopase A2 (PLA2) isozyme genes, has a region homologous to avian chicken repeat 1 (CR1)-element. In the present study, ten CR1-like elements were further identified in T. gramineus venom gland PLA2 isozyme genes, T. flavoviridis PLA2 inhibitor (PLI) genes, and T. flavoviridis and T. gramineus TATA-box binding protein (TBP) genes. Southern blot analysis using a probe for CR1 showed that Crotalinae snake genomes contain a number of CR1-like elements.

Molecular evolution of snake toxins: is the functional diversity of snake toxins associated with a mechanism of accelerated evolution?

Recent studies revealed that animal toxins with unrelated biological functions often possess a similar architecture. To tentatively understand the evolutionary mechanisms that may govern this principle of functional prodigality associated with a structural economy, two complementary approaches were considered. One of them consisted of investigating the rates of mutations that occur in cDNAs and/or genes that encode a variety of toxins with the same fold. This approach was largely adopted with phospholipases A2 from Viperidae and to a lesser extent with three-fingered toxins from Elapidae and Hydrophiidae. Another approach consisted of investigating how a given fold can accommodate distinct functional topographies. Thus, a number of topologies by which three-fingered toxins exert distinct functions were investigated either by making chemical modifications and/or mutational analyses or by studying the three-dimensional structure of toxin-target complexes. This review shows that, although the two approaches are different, they commonly indicate that most if not all the surface of a snake toxin fold undergoes natural engineering, which may be associated with an accelerated rate of evolution. The biochemical process by which this phenomenon occurs remains unknown.

High-degree sequence conservation in LPA kringle IV-type 2 exons and introns

In the search for factors contributing to the regulation of the Lp(a) lipoprotein concentration, we have sequenced the kringle IV-type 2 encoding exons 1 and 2 together with the flanking intron sequences of the LPA gene in individuals with different serum concentrations of Lp(a) lipoprotein. The high degree of sequence identity between the kringle IV-type 2 repeats made it possible to analyse all the 3-42 kringles simultaneously by polymerase chain reaction and direct DNA sequencing. The strategy used allowed us to determine approximately 700 bp from each kringle IV-type 2 repeat, resulting in a rapid screen of on average 28,000 bp of the LPA gene from each individual. Comparing these bipartite kringle IV-type 2 repeat sequences from 12 individuals with high and 11 individuals with low Lp(a) lipoprotein level revealed that: 1. no sequence polymorphism could be detected in the exons examined; 2. no sequence polymorphism could be detected in the consensus GT/AG splicing signals of exon/intron junctions; and 3. the proximal intron sequences seemed almost completely conserved in the 76-135 bp analysed. Only one position in the intron sequences exhibited the pattern of a G/A polymorphism. We observed no differences between the group with high and the group with low Lp(a) lipoprotein level. The very high conservation of intron sequences could support the hypothesis that the LPA gene evolved relatively recently. The contradictory finding of a corresponding sequence conservation between the human LPA and the plasminogen gene suggests that an evolutionary pressure has preserved these intron sequences over the last 40-90 million years.

Identification and sequence analysis of two new members of the SKALP/elafin and SPAI-2 gene family. Biochemical properties of the transglutaminase substrate motif and suggestions for a new nomenclature

The human epithelial proteinase inhibitor SKALP/elafin and the porcine sodium-potassium ATPase inhibitor SPAI-2 are two highly homologous proteins that share an NH2-terminal transglutaminase substrate domain and a COOH-terminal whey acidic protein (WAP) domain. Here we describe the bovine and simian orthologs of SKALP/elafin as well as two new bovine family members that are designated Trappin-4 and Trappin-5 on the basis of a new nomenclature that we propose (Trappin = TRansglutaminase substrate and WAP motif-containing ProteIN). Sequence analysis of Trappin-4 and Trappin-5 revealed a domain structure that is very similar to SPAI-2 (Trappin-1) and SKALP/elafin (Trappin-2). The transglutaminase substrate motifs are conserved although the number of repeats varies among species and among family members. The sequence of Trappin-4 and Trappin-5 diverges from Trappin-1 and Trappin-2 at the putative reactive site in the WAP domain. The bovine ortholog of Trappin-2 is expressed in tongue and snout epidermis; Trappin-4 is expressed in trachea, ileum, and tongue; and Trappin-5 is expressed at low levels in trachea, as determined by RNase protection and Northern blot analysis. Based on the analysis of 67 transglutaminase substrate repeats as present in all known Trappin gene family members from four different mammalian species a consensus sequence could be established: Gly-Gln-Asp-Pro-Val-Lys (GQDPVK). Using biotinylated hexapeptide probes we found that the GQDPVK sequence is a very efficient transglutaminase substrate both for guinea pig liver transglutaminase and for epidermal transglutaminase, and it acts as acyl donor as well as acceptor. We propose that the Trappin protein family forms a new group of enzyme inhibitors with various specificities of the WAP domain, which share transglutaminase substrate motifs that can act as an anchoring sequence.

cDNA cloning of a heterogeneous two-chain anticoagulant protein IX-bp

IX-bp and IX/X-bp are heterogeneous two-chain anticoagulant proteins isolated from the venom of habu snake, Trimeresurus flavoviridis. The amino acid sequence of one (B chain) of their two chains is identical. We recently reported the cloning of cDNA encoding the B chain and that of the A chain of IX/X-bp. Here, we report the isolation and characterization of cDNA clones encoding the A chain of IX-bp. The 697-bp sequence showed a putative ORF capable of encoding a 152-amino-acid protein containing a 23-amino-acid signal peptide. The overall amino acid sequence identity between the pre-A chain of IX-bp and that of IX/X-bp is 84%, whereas the cDNA sequence identity of the two ORFs is 91% indicating that habu snake acquired the variety of venom proteins by efficient mutations of antonymous sites.

Structures of genes encoding phospholipase A2 inhibitors from the serum of Trimeresurus flavoviridis snake

Inhibitors (PLIs) against snake venom gland phospholipases A2 (PLA2s) have been found in their sera. A cDNA encoding a PLI from Trimeresurus flavoviridis (Tf, habu snake, Crotalinae) serum, cPLI-A, was isolated from the Tf liver cDNA library and sequenced. Northern blot analysis with cPLI-A showed that PLIs are expressed only in liver. Genes for PLIs, gPLI-A and gPLI-B, were isolated from the Tf genomic DNA library and their nucleotide (nt) sequences were determined. The genes consisted of four exons and three introns, and exon 4 encoded the carbohydrate recognition domain (CRD)-like motif. Comparison of the nt sequences between gPLI-A and gPLI-B showed that these genes are highly homologous, including introns, except that exon 3 is rich in nonsynonymous nt substitutions which are almost four times as frequent as synonymous nt substitutions. This evolutionary feature of PLI genes is different from that of venom gland PLA2 isozyme genes in which nonsynonymous nt substitutions are spread over the entire mature protein-coding region.

Cryptic origin of SPAI, a plasma protein with a transglutaminase substrate domain and the WAP motif, revealed by in situ hybridization and immunohistochemistry

SPAI, originally isolated as a sodium/potassium-ATPase inhibitor and now considered to be a proteinase inhibitor of unknown specificity based on its similarity to elafin (an elastase inhibitor), is a new type of plasma protein that has a transglutaminase substrate domain, which serves as an anchoring sequence to be covalently cross-linked at target sites. To determine the source of SPAI, we carried out in situ hybridization and immunohistochemistry using an antisense cRNA probe and an antiserum against recombinant SPAI, respectively. Since previous RNase protection analysis had indicated that SPAI mRNA is almost exclusively expressed in the porcine small intestine, we used its frozen sections for the staining. The lower crypt was decorated with both the cRNA probe and antiserum, indicating that SPAI is synthesized and secreted by the enteroendocrine cells located near the crypt base. The native form of SPAI was also characterized by Western blotting. This result together with the previous biochemical and molecular biological characterizations may set the stage for identifying the physiological roles of the conceptually very interesting protein SPAI.