Enzyme from the medicinal leech (Hirudo medicinalis) that specifically splits endo-epsilon(-gamma-Glu)-Lys isopeptide bonds: cDNA cloning and protein primary structure

Isolation of an invertebrate-type lysozyme from the nephridia of the echiura, Urechis unicinctus, and its recombinant production and activities

Invertebrates, unlike vertebrates which have adaptive immune system, rely heavily on the innate immune system for the defense against pathogenic bacteria. Lysozymes, along with other immune effectors, are regarded as an important group in this defense. An invertebrate-type (i-type) lysozyme, designated Urechis unicinctus invertebrate-type lysozyme, Uu-ilys, has been isolated from nephridia of Urechis unicinctus using a series of high performance liquid chromatography (HPLC), and ultrasensitive radial diffusion assay (URDA) as a bioassay system. Analyses of the primary structure and cDNA cloning revealed that Uu-ilys was approximately 14 kDa and composed of 122 amino acids (AAs) of which the precursor had a total of 160 AAs containing a signal peptide of 18 AAs and a pro-sequence of 20 AAs encoded by the nucleotide sequence of 714 bp that comprises a 5' untranslated region (UTR) of 42 bp, an open reading frame (ORF) of 483 bp, and a 3' UTR of 189 bp. Multiple sequence alignment showed Uu-ilys has high homology to i-type lysozymes from several annelids. Relatively high transcriptional expression levels of Uu-ilys was detected in nephridia, anal vesicle, and intestine. The native Uu-ilys exhibited comparable lysozyme enzymatic and antibacterial activities to hen egg white lysozyme. Collectively, these data suggest that Uu-ilys, the isolated antibacterial protein, plays a role in the immune defense mechanism of U. unicinctus. Recombinant Uu-ilys (rUu-ilys) produced in a bacterial expression system showed significantly decreased lysozyme lytic activity from that of the native while its potency on radial diffusion assay detecting antibacterial activity was retained, which may indicate the non-enzymatic antibacterial capacity of Uu-ilys.

Role of isopeptidolysis in the process of thrombolysis

INTRODUCTION

Known thrombolytic agents either break peptide bonds in the fibrin molecule or act as plasminogen activators, which also results in peptide bond cleavage. In thrombi, fibrin molecules are known to be cross-linked by isopeptide bonds, the formation of which is mediated by factor XIIIa. In this work, we studied the dissolution of thrombi via isopeptide bond cleavage using a recombinant destabilase. Destabilase is an enzyme secreted from the medicinal leech salivary gland. This enzyme exhibits muramidase (lysozyme) activity, in addition to endo-ε-(γ-Glu)-Lys-isopeptidase activity, which is responsible for isopeptide bond cleavage.

METHODS

Venous (jugular vein) and arterial (carotid artery) thrombosis was induced in rats. Rats were intravenously injected with both recombinant destabilase produced in Escherichia coli and a commercial streptokinase preparation. After 24 h, the weight and degree of cross-linking in the thrombi were analysed. Amidolytic activity in rat blood serum was measured in order to evaluate destabilase levels in the blood.

RESULTS

Destabilase was definitively shown to cause a 47.6% and 74.6% decrease in the weight of venous and arterial thrombi, respectively. The enzyme proved to be more efficient at dissolving thrombi compared to streptokinase. The combined administration of destabilase and streptokinase has a greater effect than the injection of individual enzymes. Destabilase reduces fibrin stabilization in thrombi.

CONCLUSION

Cumulatively, we find that the medicinal leech destabilase is a more efficient thrombolytic agent for dissolving thrombi, which could help increase the overall effectiveness of conventional thrombolytic drugs.

Newly identified invertebrate-type lysozyme (Splys-i) in mud crab (Scylla paramamosain) exhibiting muramidase-deficient antimicrobial activity

Lysozymes are widely distributed immune effectors exerting muramidase activity against the peptidoglycan of the bacterial cell wall to trigger cell lysis. However, some invertebrate-type (i-type) lysozymes deficient of muramidase activity still exhibit antimicrobial activity. To date, the mechanism underlying the antimicrobial effect of muramidase-deficient i-type lysozymes remains unclear. Accordingly, this study characterized a novel i-type lysozyme, Splys-i, in the mud crab Scylla paramamosain. Splys-i shared the highest identity with the Litopenaeus vannamei i-type lysozyme (Lvlys-i2, 54% identity) at the amino acid level. Alignment analysis and 3D structure comparison show that Splys-i may be a muramidase-deficient i-type lysozyme because it lacks the two conserved catalytic residues (Glu and Asp) that are necessary for muramidase activity. Splys-i is mainly distributed in the intestine, stomach, gills, hepatopancreas, and hemocytes, and it is upregulated by Vibrio harveyi or Staphylococcus aureus challenge. Recombinant Splys-i protein (rSplys-i) can inhibit the growth of Gram-negative bacteria (V. harveyi, Vibrio alginolyticus, Vibrio parahemolyticus, and Escherichia coli), Gram-positive bacteria (S. aureus, Bacillus subtilis, and Bacillus megaterium), and the fungus Candida albicans to varying degrees. In this study, two binding assays and a bacterial agglutination assay were conducted to elucidate the potential antimicrobial mechanisms of Splys-i. Results demonstrated that rSplys-i could bind to all nine aforementioned microorganisms. It also exhibited a strong binding activity to lipopolysaccharide from E. coli and lipoteichoic acid and peptidoglycan (PGN) from S. aureus but a weak binding activity to PGN from B. subtilis and β-glucan from fungi. Moreover, rSplys-i could agglutinate these nine types of microorganisms in the presence of Ca²⁺ at different protein concentrations. These results suggest that the binding activity and its triggered agglutinating activity might be two major mechanisms of action to realize the muramidase-deficient antibacterial activity. In addition, rSplys-i can hydrolyze the peptidoglycan of some Gram-positive bacteria because it exhibits weak isopeptidase activities in salt and protein concentration-dependent manner. This result indicates that such an isopeptidase activity may contribute to the muramidase-deficient antimicrobial activity to a certain degree. In conclusion, Splys-i is upregulated by pathogenic bacteria, and it inhibits bacterial growth by binding and agglutination activities as well as isopeptidase activity, suggesting that Splys-i is involved in immune defense against bacteria through several different mechanisms of action.

Expression and characterization of a recombinant i-type lysozyme from the harlequin ladybird beetle Harmonia axyridis

Lysozymes are enzymes that destroy bacterial cell walls by hydrolysing the polysaccharide component of peptidoglycan. In insects, there are two classes of lysozymes, the c-type with muramidase activity and the i-type whose prototypical members from annelids and molluscs possess both muramidase and isopeptidase activities. Many insect genes encoding c-type and i-type lysozymes have been identified during genome and transcriptome analyses, but only c-type lysozymes have been functionally characterized at the protein level. Here we produced one of five i-type lysozymes represented in the immunity-related transcriptome of the invasive harlequin ladybird beetle Harmonia axyridis as recombinant protein. This was the only one containing the serine and histidine residues that are thought to be required for isopeptidase activity. This i-type lysozyme was recombinantly expressed in the yeast Pichia pastoris, but the purified protein was inactive in both muramidase and isopeptidase assays. Transcription and immunofluorescence analysis revealed that this i-type lysozyme is produced in the fat body but is not inducible by immune challenge. These data suggest that i-type lysozymes in insects may have acquired novel and as yet undetermined functions in the course of evolution.

A comparison of the enzymatic properties of three recombinant isoforms of thrombolytic and antibacterial protein--Destabilase-Lysozyme from medicinal leech

Background

Destabilase-Lysozyme (mlDL) is a multifunctional i-type enzyme that has been found in the secretions from the salivary glands of medicinal leeches. mlDL has been shown to exhibit isopeptidase, muramidase and antibacterial activity. This enzyme attracts interest because it expresses thrombolytic activity through isopeptidolysis of the ε-(γ-Glu)-Lys bonds that cross-link polypeptide chains in stabilised fibrin. To date, three isoforms of mlDL have been identified.

The enzymatic properties of pure mlDL isoforms have not yet been described because only destabilase complexes containing other proteins could be isolated from the salivary gland secretion and because low product yield from the generation of recombinant proteins has made comprehensive testing difficult.

Results

In the present study, we optimised the procedures related to the expression, isolation and purification of active mlDL isoforms (mlDL-Ds1, mlDL-Ds2, mlDL-Ds3) using an Escherichia coli expression system, and we detected and compared their muramidase, lytic, isopeptidase and antimicrobial activities. After optimisation, the product yield was 30 mg per litre of culture. The data obtained in our study led to the suggestion that the recombinant mlDL isoforms isolated from inclusion bodies form stable oligomeric complexes. Analyses of the tested activities revealed that all isoforms exhibited almost identical patterns of pH and ionic strength effects on the activities. We determined that mlDL-Ds1, 2, 3 possessed non-enzymatic antibacterial activity independent of their muramidase activity. For the first time, we demonstrated the fibrinolytic activity of the recombinant mlDL and showed that only intact proteins possessed this activity, suggesting their enzymatic nature.

Conclusions

The recombinant Destabilase-Lysozyme isoforms obtained in our study may be considered potential thrombolytic agents that act through a mechanism different from that of common thrombolytics.

Electronic supplementary material

The online version of this article (doi:10.1186/s12858-015-0056-3) contains supplementary material, which is available to authorized users.

Gene identification and recombinant protein of a lysozyme from freshwater mussel Cristaria plicata

Lysozymes are important proteins to bivalve in the innate immune responses against bacterial infections, and provide nutrition as digestion enzymes. A new LYZ1 from the freshwater mussel Cristaria plicata was cloned by rapid amplification of cDNA ends (RACE) and nested PCR method. The full-length cDNA sequence of CpLYZ1 was 763 bp. The cDNA contained a 5'-terminal untranslated region (UTR) of 21 bp, a 3'- terminal UTR of 259 bp with a 29 bp poly(A) tail, a tailing signal (AATAAA) and the open reading frame of 483 bp. The CpLYZ1 cDNA encoded a polypeptide of 160 amino acids with a predicted molecular mass of 17.8 kDa, and a theoretical isoelectric point of 6.07. The comparison of the deduced amino acid sequences with LYZs from other species showed that the enzyme belonged to i-type lysozyme. The mRNA transcript of CpLYZ1 could be detected in all the examined tissues with the highest expression level in hepatopancreas. The expression levels of CpLYZ1 in hemocytes, hepatopancreas and gill significantly increased after Aeromonas hydrophila challenge. The expression level of CpLYZ1 in hemocytes sharply decreased from 6 h to 24 h and significantly increased at 48 h, and was the highest level in hepatopancreas at 24 h, and was the maximum level in gill at 48 h. Furthermore, the recombinant CpLYZ1 was induced to be expressed as an inclusion body form by IPTG at 37 °C for 4 h, and then was purified by using the Ni(2+) affinity chromatography. The relative enzyme activity of the recombinant CpLYZ1 was influenced on pH and temperature. The optimal pH and temperature was 5.5 and 50 °C, respectively. Against Escherichia coli, A. hydrophila, Staphyloccocus aureus, Bacillus subtilis, Streptococcus sp. and Staphylococcus epidermidis, the recombinant CpLYZ1 had bacteriolytic activity.

Morphological and functional characterization of leech circulating blood cells: role in immunity and neural repair

Unlike most invertebrates, annelids possess a closed vascular system distinct from the coelomic liquid. The morphology and the function of leech blood cells are reported here. We have demonstrated the presence of a unique cell type which participates in various immune processes. In contrast to the mammalian spinal cord, the leech CNS is able to regenerate and restore function after injury. The close contact of the blood with the nerve cord also led us to explore the participation of blood in neural repair. Our data evidenced that, in addition to exerting peripheral immune functions, leech blood optimizes CNS neural repair through the release of neurotrophic substances. Circulating blood cells also appeared able to infiltrate the injured CNS where, in conjunction with microglia, they limit the formation of a scar. In mammals, CNS injury leads to the generation of a glial scar that blocks the mechanism of regeneration by preventing axonal regrowth. The results presented here constitute the first description of neuroimmune functions of invertebrate blood cells. Understanding the basic function of the peripheral circulating cells and their interactions with lesioned CNS in the leech would allow us to acquire insights into the complexity of the neuroimmune response of the injured mammalian brain.

Shrimp invertebrate lysozyme i-lyz: gene structure, molecular model and response of c and i lysozymes to lipopolysaccharide (LPS)

The invertebrate lysozyme (i-lyz or destabilase) is present in shrimp. This protein may have a function as a peptidoglycan-breaking enzyme and as a peptidase. Shrimp is commonly infected with Vibrio sp., a Gram-negative bacteria, and it is known that the c-lyz (similar to chicken lysozyme) is active against these bacteria. To further understand the regulation of lysozymes, we determined the gene sequence and modeled the protein structure of i-lyz. In addition, the expression of i-lyz and c-lyz in response to lipopolysaccharide (LPS) was studied. The shrimp i-lyz gene is interrupted by two introns with canonical splice junctions. The expression of the shrimp i-lyz was transiently down-regulated after LPS injection followed by induction after 6 h in hepatopancreas. In contrast, c-lyz was up-regulated in hepatopancreas 4 h post-injection and slightly down-regulated in gills. The L. vannamei i-lyz does not contain the catalytic residues for muramidase (glycohydrolase) neither isopeptidase activities; however, it is known that the antibacterial activity does not solely rely on the enzymatic activity of the protein. The study of invertebrate lysozyme will increase our understanding of the regulatory process of the defense mechanisms.

Destabilase-lysozyme of medicinal leech. Multifunctionality of recombinant protein

Preparation and purification of a recombinant protein are described along with characteristics of its specific (for ε-(γ-Glu)-Lys and D-dimer substrates) and nonspecific (for L-γ-Glu-pNA) isopeptidase activities; the absence of peptidase function for α-(α-Glu)-Lys substrate is noted. It is shown that the protein exhibits muramidase (cell walls of Micrococcus lysodeikticus) and specific glycosidase activities. The latter was determined towards the fluorogenic substrate 4-methylumbelliferyl-tetra-N-acetyl-β-chitotetraoxide. Antimicrobial activity of recombinant destabilase-lysozyme protein (recDest-Lys) and its 11-membered amphipathic peptide was revealed towards cells of the strict anaerobic Archaean Methanosarcina barkeri, whose cell walls contain no murein. Possible mechanisms of the effect of recDest-Lys on these cells are discussed.

Cloning and characterization of an invertebrate type lysozyme from Venerupis philippinarum

Lysozymes are key proteins to invertebrates in the innate immune responses against bacterial infections and providing nutrition as digestion enzymes. In the present study, an invertebrate type lysozyme (denoted as VpLYZ) was identified from Venerupis philippinarum haemocytes by cDNA library and RACE approaches. The full-length cDNA of VpLYZ consisted of 805 nucleotides with a canonical polyadenylation signal sequence AATAAA and a polyA tail, and an open-reading frame of 558bp encoding a polypeptide of 185 amino acids with a calculated molecular mass of 20.87kD and theoretical pI of 8.44. The high similarity of VpLYZ with other i-type lysozymes from mollusk indicated that VpLYZ should be a new member of i-type lysozyme family. Similar to most i-type lysozymes, VpLYZ possessed all conserved features critical for the fundamental structure and function of i-type lysozymes, such as three catalytic residues (Glu19, Asn72 and Ser75) and i-type specific motif CL(E/L/R/H)C(I/M)C. By semi-quantitative RT-PCR analysis, mRNA transcript of VpLYZ was found to be most abundantly expressed in the tissues of gills, hepatopancreas and haemocytes, weakly expressed in the tissues of muscle, foot and mantle. After clams were challenged by Vibrio anguillarum, the mRNA level of VpLYZ in overall haemocyte population was recorded by quantitative real-time RT-PCR. VpLYZ mRNA was down-regulated sharply from 6h to 12h post-infection. Then, the expression level increased to the peak at 72h and recovered to the original level at 96h. All these results indicated that VpLYZ was involved in the immune response against microbe infection and contributed to the clearance of bacterial pathogens.

Crystal Structure of Tapes japonica Lysozyme with Substrate Analogue

Tapes japonica lysozyme (TJL) is classified as a member of the recently established i-type lysozyme family. In this study, we solved the crystal structure of TJL complexed with a trimer of N-acetylglucosamine to 1.6A resolution. Based on structure and mutation analyses, we demonstrated that Glu-18 and Asp-30 are the catalytic residues of TJL. Furthermore, the present findings suggest that the catalytic mechanism of TJL is a retaining mechanism that proceeds through a covalent sugar-enzyme intermediate. On the other hand, the quaternary structure in the crystal revealed a dimer formed by the electrostatic interactions of catalytic residues (Glu-18 and Asp-30) in one molecule with the positive residues at the C terminus in helix 6 of the other molecule. Gel chromatography analysis revealed that the TJL dimer remained intact under low salt conditions but that it dissociated to TJL monomers under high salt conditions. With increasing salt concentrations, the chitinase activity of TJL dramatically increased. Therefore, this study provides novel evidence that the lysozyme activity of TJL is modulated by its quaternary structure.

Expression profiling of GABAergic motor neurons in Caenorhabditis elegans

Neurons constitute the most diverse cell types and acquire their identity by the activity of particular genetic programs . The GABAergic nervous system in C. elegans consists of 26 neurons that fall into six classes . Animals that are defective in GABAergic neuron function and development display "shrinker" movement , abnormal foraging and defecation . Among the known shrinker genes, unc-25 and unc-47 encode the GABA biosynthetic enzyme glutamic acid decarboxylase and vesicular transporter, respectively . unc-30 encodes a homeodomain protein of the Pitx family and regulates the differentiation of the D-type GABAergic neurons . unc-46 probably functions in presynaptic GABA release , but its identity has not been reported. By cell-based microarray analysis, we identified over 250 genes with enriched expression in GABAergic neurons. The highly enriched gene set included all known genes. In vivo expression study with computational predictions further identified six new genes that are potential transcriptional targets of UNC-30. Behavioral studies of a deletion mutant implicate a function of a nicotinic receptor subunit in D-type neurons. Our analysis demonstrates the utility of neuron-specific genomics in identifying cell-specific genes and regulatory networks.

Purification and characterization of lysozyme from plasma of the eastern oyster (Crassostrea virginica)

Lysozyme was purified from the plasma of eastern oysters (Crassostrea virginica) using a combination of ion exchange and gel filtration chromatographies. The molecular mass of purified lysozyme was estimated at 18.4 kDa by SDS-PAGE, and its isoelectric point was greater than 10. Mass spectrometric analysis of the purified enzyme revealed a high-sequence homology with i-type lysozymes. No similarity was found however between the N-terminal sequence of oyster plasma lysozyme and N-terminal sequences of other i-type lysozymes, suggesting that the N-terminal sequences of the i-type lysozymes may vary to a greater extent between species than reported in earlier studies. The optimal ionic strength, pH, cation concentrations, sea salt concentrations, and temperature for activity of the purified lysozyme were determined, as well as its temperature and pH stability. Purified oyster plasma lysozyme inhibited the growth of Gram-positive bacteria (e.g., Lactococcus garvieae, Enterococcus sp.) and Gram-negative bacteria (e.g., Escherichia coli, Vibrio vulnificus). This is a first report of a lysozyme purified from an oyster species and from the plasma of a bivalve mollusc.

The lysozyme of the starfish Asterias rubens. A paradigmatic type i lysozyme

On the basis of a partial N-terminal sequence, Jollès and Jollès previously proposed that the lysozyme from the starfish Asterias rubens represents a new form of lysozyme, called type i (invertebrate) lysozyme. Indeed, it differed from both the types c (chicken) and g (goose) known in other animals, as well as from plant and phage lysozymes. Recently, several proteins belonging to the same family have been isolated from protostomes. Here we report the complete mature protein sequence and cDNA sequence of the lysozyme from Asterias. These sequences vindicate the previously proposed homology between the starfish, a deuterostome, and protostome lysozymes. In addition, we present a structural analysis that allows us to postulate upon the function of several conserved residues.

Multiple forms of medicinal leech destabilase-lysozyme

Earlier, three genes Ds1, Ds2, and Ds3 encoding corresponding destabilase-lysozyme isoforms were identified. However only one form of the enzyme encoded by Ds3 gene coincided with the protein CNBr fragments [Mol. Gen. Genet. 253 (1996) 20]. In this work we found by ESI-TOF mass spectrometry that the enzyme preparation consists of at least three forms with molecular masses of 12677.6, 12839.7, and 12938.2Da, each of which contains seven disulfide bridges. Only one mass (12839.7Da) fits to the calculated mass for the protein encoded by Ds3 gene. Further analysis of the CNBr fragments of the enzyme showed the heterogeneity of large 5.5 kDa peptide at positions 64 (threonine or arginine) and 67 (histidine or arginine) in the wild-type amino acid sequence. One CNBr peptide, with Arg and His at positions 64 and 67, respectively, correlates in the molecular mass with the protein encoded by Ds3. In addition, we have found a new acid form of destabilase-lysozyme, P-Ac, which differs from all known destabilase-lysozyme structures by its N-terminal amino acid sequence.

Destabilase from the medicinal leech is a representative of a novel family of lysozymes

Intrinsic lysozyme-like activity was demonstrated for destabilase from the medicinal leech supported by (1) high specific lysozyme activity of the highly purified destabilase, (2) specific inhibition of the lysozyme-like activity by anti-destabilase antibodies, and (3) appreciable lysozyme-like activity in insect cells infected with recombinant baculoviruses carrying cDNAs encoding different isoforms of destabilase. Several isoforms of destabilase constitute a protein family at least two members of which are characterized by lysozyme activity. The corresponding gene family implies an ancient evolutionary history of the genes although the function(s) of various lysozymes in the leech remains unclear. Differences in primary structures of the destabilase family members and members of known lysozyme families allow one to assign the former to a new family of lysozymes. New proteins homologous to destabilase were recently described for Caenorhabditis elegans and bivalve mollusks suggesting that the new lysozyme family can be widely distributed among invertebrates. It remains to be investigated whether the two enzymatic activities (isopeptidase and lysozyme-like) are attributes of one and the same protein.

Amino acid sequences of lysozymes newly purified from invertebrates imply wide distribution of a novel class in the lysozyme family

Lysozymes were purified from three invertebrates: a marine bivalve, a marine conch, and an earthworm. The purified lysozymes all showed a similar molecular weight of 13 kDa on SDS/PAGE. Their N-terminal sequences up to the 33rd residue determined here were apparently homologous among them; in addition, they had a homology with a partial sequence of a starfish lysozyme which had been reported before. The complete sequence of the bivalve lysozyme was determined by peptide mapping and subsequent sequence analysis. This was composed of 123 amino acids including as many as 14 cysteine residues and did not show a clear homology with the known types of lysozymes. However, the homology search of this protein on the protein or nucleic acid database revealed two homologous proteins. One of them was a gene product, CELF22 A3.6 of C. elegans, which was a functionally unknown protein. The other was an isopeptidase of a medicinal leech, named destabilase. Thus, a new type of lysozyme found in at least four species across the three classes of the invertebrates demonstrates a novel class of protein/lysozyme family in invertebrates. The bivalve lysozyme, first characterized here, showed extremely high protein stability and hen lysozyme-like enzymatic features.

Hydrolysis of gamma:epsilon isopeptides by cytosolic transglutaminases and by coagulation factor XIIIa

Nepsilon-(gamma-glutamyl)lysine cross-links, connecting various peptide chain segments, are frequently the major products in transglutaminase-catalyzed reactions. We have now investigated the effectiveness of these enzymes for hydrolyzing the gamma:epsilon linkage. Branched compounds were synthesized, in which the backbone on the gamma-side of the cross-bridge was labeled with a fluorophor (5-(dimethylamino)-1-naphthalenesulfonyl or 2-aminobenzoyl) attached through an epsilon-aminocaproyl linker in the N-terminal position, and the other branch of the bridge was constructed with Lys methylamide or diaminopentane blocked by 2,4-dinitrophenyl at the Nalpha position. Hydrolysis of the cross-link could be followed in these internally quenched substrates by an increase in fluorescence. In addition to the thrombin and Ca2+-activated human coagulation Factor XIIIa, cytosolic transglutaminases from human red cells and from guinea pig liver were tested. All three enzymes were found to display good isopeptidase activities, with Km values of 10(-4) to 10(-5) M. Inhibitors of transamidation were effective in blocking the hydrolysis by the enzymes, indicating that expression of isopeptidase activity did not require unusual protein conformations. We suggest that transglutaminases may play a dynamic role in biology not only by promoting the formation but also the breaking of Nepsilon-(gamma-glutamyl)lysine isopeptides.