Pigment epithelium-derived factor: a multimodal tumor inhibitor

Pigment epithelium-derived factor (PEDF), a noninhibitory member of the serine protease inhibitor (serpin) family, is a well-known potent endogenous inhibitor of angiogenesis. It has been known for years to be aberrantly expressed in ocular disorders, but in recent years, down-regulation has been shown to be prevalent in a range of cancers as well. This review describes the trimodal anticancer activities of this interesting protein: antiangiogenesis, apoptosis-mediated tumor suppression, and tumor cell differentiation. The key to successful antitumor therapy with this protein is the ability to synthesize the recombinant form of the protein (or its active shortened forms) and deliver at therapeutic doses or alternatively to use gene transfer technology to prolong the effect in vivo. Although there is a substantial amount of work carried out at the preclinical stage with this protein, more groundwork has to be done before PEDF is tested against cancer in clinical trials.

The reactive site loop of the serpin SCCA1 is essential for cysteine proteinase inhibition

The high-molecular-weight serine proteinase inhibitors (serpins) are restricted, generally, to inhibiting proteinases of the serine mechanistic class. However, the viral serpin, cytokine response modifier A, and the human serpins, antichymotrypsin and squamous cell carcinoma antigen 1 (SCCA1), inhibit different members of the cysteine proteinase class. Although serpins employ a mobile reactive site loop (RSL) to bait and trap their target serine proteinases, the mechanism by which they inactivate cysteine proteinases is unknown. Our previous studies suggest that SCCA1 inhibits papain-like cysteine proteinases in a manner similar to that observed for serpin-serine proteinase interactions. However, we could not preclude the possibility of an inhibitory mechanism that did not require the serpin RSL. To test this possibility, we employed site-directed mutagenesis to alter the different residues within the RSL. Mutations to either the hinge or the variable region of the RSL abolished inhibitory activity. Moreover, RSL swaps between SCCA1 and the nearly identical serpin, SCCA2 (an inhibitor of chymotrypsin-like serine proteinases), reversed their target specificities. Thus, there were no unique motifs within the framework of SCCA1 that independently accounted for cysteine proteinase inhibitory activity. Collectively, these data suggested that the sequence and mobility of the RSL of SCCA1 are essential for cysteine proteinase inhibition and that serpins are likely to utilize a common RSL-dependent mechanism to inhibit both serine and cysteine proteinases.

Functional analysis of Toxoplasma gondii protease inhibitor 1

We have characterized a Kazal family serine protease inhibitor, Toxoplasma gondii protease inhibitor 1 (TgPI-1), in the obligate intracellular parasite Toxoplasma gondii. TgPI-1 contains four inhibitor domains predicted to inhibit trypsin, chymotrypsin, and elastase. Antibodies against recombinant TgPI-1 detect two polypeptides, of 43 and 41 kDa, designated TgPI-1(43) and TgPI-1(41), in tachyzoites, bradyzoites, and sporozoites. TgPI-1(43) and TgPI-1(41) are secreted constitutively from dense granules into the excreted/secreted antigen fraction as well as the parasitophorous vacuole that T. gondii occupies during intracellular replication. Recombinant TgPI-1 inhibits trypsin, chymotrypsin, pancreatic elastase, and neutrophil elastase. Immunoprecipitation studies with anti-rTgPI-1 antibodies reveal that recombinant TgPI-1 forms a complex with trypsin that is dependent on interactions with the active site of the protease. TgPI-1 is the first anti-trypsin/chymotrypsin inhibitor to be identified in bradyzoites and sporozoites, stages of the parasite that would be exposed to proteolytic enzymes in the digestive tract of the host.

Primary structure of the human elafin precursor preproelafin deduced from the nucleotide sequence of its gene and the presence of unique repetitive sequences in the prosegment

The human elafin gene was cloned and its entire nucleotide sequence was determined to deduce the amino acid sequence for the precursor of elafin, an elastase-specific inhibitor. The gene spans approximately 1.7 kb and is divided into 3 exons. The gene product preproelafin consists of 117 amino acids: the initiator Met, a putative 25-amino acid signal peptide, a pro-sequence of about 34 amino acids, and the C-terminal 57 amino acids for mature elafin. Possible covalent clotting of the prosegment and its physiological significance have been pointed out based on a remarkable sequence similarity between the pro-sequence and the guinea pig seminal clotting protein SVP-1.

Infestin, a thrombin inhibitor presents in Triatoma infestans midgut, a Chagas' disease vector: gene cloning, expression and characterization of the inhibitor

This work describes the purification, gene cloning and expression of infestin, a thrombin inhibitor from midguts of Triatoma infestans. Infestin is located in the midgut and its purification was performed by anion-exchange and affinity chromatographies. The N-terminal sequence and the sequence of tryptic peptides were determined. Using RT-PCR, total RNA and infestin cDNA information, a DNA fragment was cloned which encodes a multi non-classical Kazal-type serine protease inhibitor. Isolated native infestin has two non-classical Kazal-type domains and shows an apparent molecular mass of 13 kDa, while its gene codes for a protein with four non-classical Kazal-type domains corresponding to an apparent molecular mass of 22 kDa. Two recombinant infestins, r-infestin 1-2 and r-infestin 1-4, were constructed using the vector pVT102U/alpha and expressed in S. cerevisiae. Native and r-infestin 1-2 showed very similar inhibitory activities towards thrombin and trypsin with dissociation constants of 43.5 and 25 pM for thrombin and 2.0 and 3.1 nM for trypsin, respectively. No other serine protease of the blood coagulation cascade was inhibited by the r-infestin 1-2. Surprisingly, r-infestin 1-4 inhibited not only thrombin and trypsin (K(i) of 0.8 and 5.2 nM, respectively), but also factor XIIa, factor Xa and plasmin (K(i) of 78 pM, 59.2 and 1.1 nM, respectively).

The crystal structure of bikunin from the inter-alpha-inhibitor complex: a serine protease inhibitor with two Kunitz domains

Bikunin is a serine protease inhibitor found in the blood serum and urine of humans and other animals. Its sequence shows internal repetition, suggesting that it contains two domains that resemble bovine pancreatic trypsin inhibitor (BPTI). A fragment of bikunin has been crystallised, its structure solved and subsequently refined against 2.5 A data. The two BPTI-like domains pack closely together and are related by an approximate 60 degrees rotation combined with a translation. These domains are very similar to each other and other proteins with this fold. The largest variations occur in the loops responsible for protease recognition. The loops of the first domain are unobstructed by the remaining protein. However, the loops of the second domain are close to the first domain and it is possible that protease binding may be affected or, in some cases, abolished by the presence of the first domain. Thus, cleavage of the two domains could alter the substrate specificity of domain II. Bikunin has a hydrophobic patch close to the N terminus of domain I, which is the most likely site for cell-surface receptor binding. In addition, there is a basic patch at one end of domain II that may be responsible for the inhibition of calcium oxalate crystallization in urine.

Plasminogen activator inhibitor-1 in vascular thrombosis

Thrombotic complications of vascular disease constitute the leading cause of morbidity and mortality in much of the developed world. Current drug therapies available to treat the thrombotic component of arterial and venous vascular complications remain limited. Novel safe and effective treatment strategies to reduce formation of occlusive thrombosis will likely have a major impact on reducing the economic burden of vascular disease on the healthcare system. Enhancing endogenous fibrinolysis by targeting plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor of circulating plasminogen activators, has been shown to be effective in markedly attenuating the formation of arterial and venous occlusive thrombosis in animal models. In addition, animal and human studies of PAI-1 deficiency indicate that spontaneous bleeding complications associated with even complete PAI-1 deficiency would be rare. Patients most likely to benefit from PAI-1 inhibition would be those at high risk for vascular events where PAI-1 is elevated, such as is observed in obesity, diabetes and the metabolic syndrome. Since obesity and metabolic syndrome are now epidemic, and will likely have a major adverse impact on vascular thrombotic events, it may be time to test the clinical effectiveness of PAI-1 inhibition in a patient population at high risk for vascular thrombosis.

Multiple murine alpha 1-protease inhibitor genes show unusual evolutionary divergence

The murine alpha 1-protease inhibitors (alpha 1-PI) are encoded by a small gene family on chromosome 12. Studies of alpha 1-PI and other serine protease inhibitor genes have revealed an unusually high rate of mutation of the reactive centers of the inhibitors. Using a modification of the PCR technique, we have previously identified five distinct alpha 1 PI reactive site sequences present in the genome of C57BL/6 mice. In this report, we use cDNA cloning techniques to demonstrate that all five genes are expressed in the adult mouse liver. DNA sequence analysis shows that three of the five mRNAs expressed have a substitution for methionine-353, which is essential for normal activity of the homologous human protein, alpha 1-antitrypsin (alpha 1-AT). Comparison of the DNA sequences of the five cDNAs indicates a higher degree of polymorphism in the carboxyl-terminal half of the protein and an extraordinarily replacement/silent ratio of nucleotide changes in a narrow region surrounding the reactive site. The clustering of polymorphisms near the reactive site combined with the high replacement/silent ratio suggest an evolutionary mechanism that apparently selects for functional diversity of the alpha 1-PI genes. Finally, modeling of the three-dimensional positions of the alpha 1-PI polymorphic residues into the homologous positions of the crystallographic structure of ovalbumin, a member of the alpha 1-PI supergene family, predicts that many of these amino acids are on the surfaces, which are likely to interact with the protease targets.

Secretion of mucus proteinase inhibitor and elafin by Clara cell and type II pneumocyte cell lines

The regulation of proteinases secreted by neutrophils is very important for the prevention of tissue injury. We recently described the isolation of elafin from bronchial secretions, a new elastase-specific inhibitor that is also found in the skin of patients with psoriasis. In this study, we investigated the secretion of elafin and mucus proteinase inhibitor (MPI), another inhibitor showing sequence similarity with elafin, in two lung carcinoma cell lines, NCI-H322 and A549, which have features of Clara cells and type II alveolar cells, respectively. The results presented show that the two inhibitors are produced when the cells are cultured either in serum-free or in serum-containing media. MPI was detected immunologically as a unique molecule of M(r) 14 kD, in accordance with previous studies. Conversely, one or two elafin-immunoreactive species were detected depending on the cell line: a 12- to 14-kD species was observed in the A549 cell line, regardless of the culture conditions, whereas in the NCI-H322 cell line we detected a 6-kD species in serum-containing (10% fetal calf serum) conditions and a 12- to 14-kD species in serum-free conditions. The 12- to 14-kD molecule probably represents an active precursor of elafin. Whether the cleavage of the 12- to 14-kD precursor giving rise to the elafin molecule is of any physiologic significance is not known. In showing for the first time that MPI and elafin (and its precursor) are secreted by the A549 cell line, this report implicates the type II alveolar cell in the defense of the peripheral lung against the neutrophil elastase secreted during inflammation.

Inhibition of retinoblastoma protein degradation by interaction with the serpin plasminogen activator inhibitor 2 via a novel consensus motif

Plasminogen activator inhibitor-2 (PAI-2) is well documented as an inhibitor of the extracellular serine proteinase urokinase-type plasminogen activator (uPA) and is expressed in activated monocytes and macrophages, differentiating keratinocytes, and many tumors. Here we show that PAI-2 has a novel intracellular function as a retinoblastoma protein (Rb)-binding protein. PAI-2 colocalized with Rb in the nucleus and inhibited the turnover of Rb, which led to increases in Rb protein levels and Rb-mediated activities. Although PAI-2 contains an LXCXE motif, Rb binding was primarily mediated by the C-D interhelical region of PAI-2, which was found to bind to the C pocket of Rb. The C-D interhelical region of PAI-2 contained a novel Rb-binding motif, termed the PENF homology motif, which is shared by many cellular and viral Rb-binding proteins. PAI-2 expression also protected Rb from the accelerated degradation mediated by human papillomavirus (HPV) E7, leading to recovery of Rb and inhibition of E6/E7 mRNA expression. Protection of Rb by PAI-2 begins to explain many of the diverse, uPA-independent phenotypes conferred by PAI-2 expression. These results indicate that PAI-2 may enhance Rb's tumor suppressor activity and suggest a potential therapeutic role for PAI-2 against HPV-transformed lesions.

Regulation of pro-apoptotic leucocyte granule serine proteinases by intracellular serpins

Caspase activation and apoptosis can be initiated by the introduction of serine proteinases into the cytoplasm of a cell. Cytotoxic lymphocytes have evolved at least one serine proteinase with specific pro-apoptotic activity (granzyme B), as well as the mechanisms to deliver it into a target cell, and recent evidence suggests that other leucocyte granule proteinases may also have the capacity to kill if released into the interior of cells. For example, the monocyte/granulocyte proteinase cathepsin G can activate caspases in vitro, and will induce apoptosis if its entry into cells is mediated by a bacterial pore-forming protein. The potent pro-apoptotic activity of granzyme B and cathepsin G suggests that cells producing these (or other) proteinases would be at risk from self-induced death if the systems involved in packaging, degranulation or targeting fail and allow proteinases to enter the host cell cytoplasm. The purpose of the present review is to describe recent work on a group of intracellular serine proteinase inhibitors (serpins) which may function in leucocytes to prevent autolysis induced by the granule serine proteinases.

Domain inhibitory and bacteriostatic activities of the five-domain Kazal-type serine proteinase inhibitor from black tiger shrimp Penaeus monodon

Serine proteinase inhibitors (SPIs) in multi-cellular organisms are important modulators of proteinase activities in various biological processes. A five-domain Kazal-type SPI SPIPm2 from the black tiger shrimp Penaeus monodon is presumably involved in innate immune response. The SPIPm2 with the domain P1 residues T, A, E, K and E was isolated from the hemocyte cDNA libraries and found to strongly inhibit subtilisin and elastase, and weakly inhibit trypsin. To unravel further the inhibitory activity of each domain, we subcloned, over-expressed and purified each individual SPI domain. Their inhibitory specificities against trypsin, subtilisin and elastase were determined. Domain 1 was found to be inactive. Domains 2, 3 and 5 inhibited subtilisin. Domain 2 inhibited also elastase. Domain 4 weakly inhibited subtilisin and trypsin. The intact SPIPm2 inhibitor was found to possess bacteriostatic activity against the Bacillus subtilis but not the Bacillus megaterium, Staphylococcus aureus, Vibrio harveyi 639 and Escherichia coli JM109. Domains 2, 4 and 5 contributed to this bacteriostatic activity.

Engineering of a macromolecular scaffold to develop specific protease inhibitors

The specific inhibition of serine proteases, which are crucial switches in many physiologically important processes, is of value both for basic research and for therapeutic applications. Ecotin, a potent macromolecular inhibitor of serine proteases of the S1A family, presents an attractive scaffold to engineer specific protease inhibitors because of its large inhibitor-protease interface. Using synthetic shuffling in combination with a restricted tetranomial diversity, we created ecotin libraries that are mutated at all 20 amino acid residues in the binding interface. The efficacy of these libraries was demonstrated against the serine protease plasma kallikrein (Pkal). Competitive phage display selection yielded a Pkal inhibitor with an apparent dissociation equilibrium constant (K(i)*) of 11 pM, whereas K(i)* values for related proteases (such as Factor Xa (FXa), Factor XIa (FXIa), urokinase-type plasminogen activator (uPA), thrombin, and membrane-type serine protease 1 (MT-SP1)) were four to seven orders of magnitude higher. The adaptability of the scaffold was demonstrated by the isolation of inhibitors to two additional serine proteases, MT-SP1/matriptase and Factor XIIa.

Co-localization of tissue factor and tissue factor pathway inhibitor in coronary atherosclerosis

Tissue factor (TF) initiates the extrinsic pathway of blood coagulation by acting as a cofactor for Factor VII. Inhibition of the Factor VIIa-TF complex is mediated by the tissue factor pathway inhibitor (TFPI), which is a serine protease inhibitor with three Kunitz-type domains. The localization of TF and TFPI protein has been examined immunohistochemically in various atherosclerotic lesions of coronary arteries from 22 autopsy cases and their messenger RNA expression has been confirmed by reverse transcription-polymerase chain reaction. Four types of atherosclerotic lesion (types I, II, III, and IV) were classified according to the method described by Stary et al. TF and TFPI were localized in endothelial cells, macrophages, macrophage-derived foam cells, and smooth muscle cells in the intimal lesions, medial smooth muscle cells, and endothelial cells of the microvessels in the adventitia. Immunohistochemical double staining revealed the co-localization of TF and TFPI in the endothelial cells and macrophages in four types of atherosclerotic lesions. In type III and IV lesions, the number of TF- and TFPI-positive cells was increased, accompanied by extracellular localization of TF and TFPI in the lipid core of atherosclerotic plaques. Fibrin deposition was found around TF- and TFPI-positive macrophages and in the lipid core of atherosclerotic plaques. TF and TFPI messenger RNA were detected more frequently in coronary arteries with type III and IV lesions than in those with type I and II lesions. The co-localization of TF and TFPI was demonstrated in various atherosclerotic lesions of coronary arteries and was shown to be intimately related to fibrin deposition in advanced atherosclerotic plaques. The co-localization of TF and TFPI may thus be closely associated with thrombogenicity in atherosclerotic lesions of coronary arteries.

Purification and characterization of Manduca sexta serpin-6: a serine proteinase inhibitor that selectively inhibits prophenoloxidase-activating proteinase-3

The proteolytic activation of prophenoloxidase (proPO) is a critical defense mechanism in insects and crustaceans. We have isolated three prophenoloxidase-activating proteinases (PAPs) from cuticular extracts or hemolymph of Manduca sexta pharate pupae, which are negatively regulated by serpin-1J and serpin-3. To test if other serpins may also inhibit the PAPs, we fractionated the induced hemolymph by ammonium sulfate precipitation, gel filtration, and lectin affinity chromatography. A 47 kDa protein, designated M. sexta serpin-6, was identified in concanavalin A-bound fractions, which formed an SDS-stable complex with PAP-3. This inhibitor, not recognized by the serpin-1 or serpin-3 antibodies, was further purified on HPLC anion exchange and hydroxylapatite columns. The molecular mass and isoelectric point of serpin-6 were found to be 46,710 +/- 10 Da and 5.4. While its amino terminus was blocked, we obtained five internal peptide sequences, one of which is highly similar to M. sexta serpins-1, -2, and -3. Serpin-6 strongly inhibited PAP-3 but not PAP-1 or PAP-2, suggesting that the proPO activation by PAPs is differentially regulated by multiple serpins. When included in the reaction mixture containing proPO, PAP-3, and its cofactor, serpin-6 efficiently blocked the cleavage activation of proPO.

Plasminogen activator inhibitor type 2: a regulator of monocyte proliferation and differentiation

We have explored the role of plasminogen activator inhibitor type 2 (PAI-2) in THP-1 monocyte-like cells. These cells possess a mutation in the PAI-2 gene and do not produce an active PAI-2 protein. Transfection of THP-1 cells with plasmids expressing active PAI-2 reduced the cells' inherent adhesive properties and decreased the rate of cell proliferation. THP-1 cells expressing active PAI-2 also displayed an altered phenotype in response to phorbol ester-induced differentiation that was concomitant with a reduction in CD14 expression. THP-1 cells transfected with a variant PAI-2 containing a mutation in the reactive center (PAI-2(Ala380)) displayed no noticeable change in any of these parameters, suggesting the involvement of a PAI-2-sensitive serine protease(s). The antiproliferative effect of PAI-2 was attenuated by treating the PAI-2-expressing THP-1 cells with recombinant urokinase (u-PA), suggesting that PAI-2 was disruptive of a u-PA/u-PA receptor signaling pathway initiated on the cell surface. Consistent with this, treatment of wild-type THP-1 cells with recombinant PAI-2 also caused a reduction in cellular proliferation. These results implicate endogenous PAI-2 as a modulator of monocyte adhesion, proliferation, and differentiation.

Changes in the extracellular proteome caused by the absence of the bldA gene product, a developmentally significant tRNA, reveal a new target for the pleiotropic regulator AdpA in Streptomyces coelicolor

The extracellular proteome of Streptomyces coelicolor grown in a liquid medium was analyzed by using two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization-time of flight peptide mass fingerprint analysis. Culture supernatants became protein rich only after rapid growth had been completed, supporting the idea that protein secretion is largely a stationary phase phenomenon. Out of about 600 protein spots observed, 72 were characterized. The products of 47 genes were identified, with only 11 examples predicted to be secreted proteins. Mutation in bldA, previously known to impair the stationary phase processes of antibiotic production and morphological differentiation, also induced changes in the extracellular proteome, revealing even greater pleiotropy in the bldA phenotype than previously known. Four proteins increased in abundance in the bldA mutant, while the products of 11 genes, including four secreted proteins, were severely down-regulated. Although bldA encodes the only tRNA capable of efficiently translating the rare UUA (leucine) codon, none of the latter group of genes contains an in-frame TTA. SCO0762, a serine-protease inhibitor belonging to the Streptomyces subtilisin inhibitor family implicated in differentiation in other streptomycetes, was completely absent from the bldA mutant. This dependence was shown to be mediated via the TTA-containing regulatory gene adpA, also known as bldH, a developmental gene that is responsible for the effects of bldA on differentiation. Mutation of the SCO0762 gene abolished detectable trypsin-protease inhibitory activity but did not result in any obvious morphological defects.

Differential gene expression for suicide-substrate serine proteinase inhibitors (serpins) in vegetative and grain tissues of barley

Proteins of the serpin superfamily (approximately 43 kDa) from mature cereal grains are in vitro suicide-substrate inhibitors of specific mammalian serine proteinases of the chymotrypsin family. However, unlike the 'standard-mechanism' serine proteinase inhibitors (<25 kDa), the biological functions of plant serpins are unknown. Expression studies of genes encoding members of three subfamilies of serpins (BSZx, BSZ4 and BSZ7) in developing grain and vegetative tissues of barley (Hordeum vulgare L.) showed that transcripts encoding BSZx, which inhibits distinct proteinases at overlapping reactive centres in vitro, were ubiquitous at low levels, but the protein could not be detected. EST analysis showed that expression of genes for serpins with BSZx-type reactive centres in vegetative tissues is widespread in the plant kingdom, suggesting a common regulatory function. For BSZ4 and BSZ7, expression at the protein level was highest in the maturing grain (> or d post-anthesis), where these serpins were localized by immunomicroscopy to the central and peripheral starchy endosperm, subaleurone, and (at lower levels) to the aleurone. Serpins were also localized to the meristem and vascular tissues of roots, and to the phloem of coleoptiles and leaves. The identification of BSZ4 in vegetative tissues by western blotting was confirmed for the roots by purification and amino acid sequencing, and for the leaves by in vitro reactive-centre loop cleavage studies. Plant serpins are likely to use their irreversible inhibitory mechanism in the inhibition of exogenous proteinases capable of breaking down seed storage proteins, and in the defence of specific cell types in vegetative tissues.

PIVL, a new serine protease inhibitor from Macrovipera lebetina transmediterranea venom, impairs motility of human glioblastoma cells

A novel Kunitz-type serine proteinase inhibitor, termed PIVL, was purified to homogeneity from the venom of the Tunisian snake Macrovipera lebetina transmediterranea. It is a monomeric polypeptide chain cross-linked by three disulfide linkages with an isotope-averaged molecular mass of 7691.7 Da. The 67-residue full-length PIVL sequence was deduced from a venom gland cDNA clone. Structurally, PIVL is built by a single Kunitz/BPTI-like domain. Functionally, it is able to specifically inhibit trypsin activity. Interestingly, PIVL exhibits an anti-tumor effect and displays integrin inhibitory activity without being cytotoxic. Here we show that PIVL is able to dose-dependently inhibit the adhesion, migration and invasion of human glioblastoma U87 cells. Our results also show that PIVL impairs the function of αvβ3 and to a lesser extent, the activity of αvβ6, αvβ5, α1β1 and α5β1 integrins. Interestingly, we demonstrate that the (41)RGN(43) motif of PIVL is likely responsible for its anti-cancer effect. By using time lapse videomicroscopy, we found that PIVL significantly reduced U87 cells motility and affected cell directionality persistence by 68%. These findings reveal novel pharmacological effects for a Kunitz-type serine proteinase inhibitor.

A tick protein with a modified Kunitz fold inhibits human tryptase

TdPI, a tick salivary gland product related to Kunitz/BPTI proteins is a potent inhibitor of human beta-tryptase. Kinetic assays suggest that three of the four catalytic sites of tryptase are blocked by TdPI, and that the inhibition of one of these involves a peptide flanking the Kunitz head. In the course of the inhibition, tryptase cleaves TdPI at several positions. Crystal structures of the TdPI head, on its own and in complex with trypsin, reveal features that are not found in classical Kunitz/BPTI proteins and suggest the mode of interaction with tryptase. The loop of TdPI connecting the beta-sheet with the C-terminal alpha-helix is shortened, the disulphide-bridge pattern altered and N and C termini separated to produce a highly pointed molecule capable of penetrating the cramped active sites of tryptase. TdPI accumulates in the cytosolic granules of mast cells, presumably suppressing inflammation in the host animal's skin by tryptase inhibition.

Molecular mousetraps and the serpinopathies1

Members of the serine proteinase inhibitor or serpin superfamily inhibit their target proteinases by a remarkable conformational transition that involves the enzyme being translocated more than 70 Å (1 Å=10−10 m) from the upper to the lower pole of the inhibitor. This elegant mechanism is subverted by point mutations to form ordered polymers that are retained within the endoplasmic reticulum of secretory cells. The accumulation of polymers underlies the retention of mutants of α1-antitrypsin and neuroserpin within hepatocytes and neurons to cause cirrhosis and dementia respectively. The formation of polymers results in the failure to secrete mutants of other members of the serpin superfamily: antithrombin, C1 inhibitor and α1-antichymotrypsin, to cause a plasma deficiency that results in the clinical syndromes of thrombosis, angio-oedema and emphysema respectively. Understanding the common mechanism underlying the retention and deficiency of mutants of the serpins has allowed us to group these conditions as the serpinopathies. We review in this paper the molecular and structural basis of the serpinopathies and show how this has allowed the development of specific agents to block the polymerization that underlies disease.

Human neuroserpin (PI12): cDNA cloning and chromosomal localization to 3q26

Neuroserpin is a novel serine protease inhibitor of the serpin family. It has been reported as a 55-kDa glycoprotein that is secreted from the axons of cultured central and peripheral nervous system neurons. In situ hybridization and Northern blot analyses at different developmental stages of the chicken revealed that neuroserpin is predominantly expressed in the nervous system and that most cells expressing neuroserpin can be qualified as bona fide neurons. We have isolated the full-length cDNA for human neuroserpin from a fetal retina cDNA library. The open reading frame of the cDNA of human neuroserpin, like that of its chicken counterpart, encodes a protein of 410 amino acids. The human and the chicken neuroserpin exhibit an amino acid sequence identity of 80%. Northern blot analysis of human organs demonstrated predominant expression of neuroserpin in the brain. By fluorescence in situ hybridization the human neuroserpin gene (HGMW-approved symbol PI12) was mapped to region q26 of chromosome 3.

Molecular evolution of the wound-induced serine protease inhibitor wip1 in Zea and related genera

Plant defense mechanisms have been the subject of intensive investigation. However, little is known about their long-term evolutionary dynamics. We investigated the molecular diversity of a wound-induced serine protease inhibitor, wip1, in the genus Zea, as well as the divergence of wip1 among four genera, Zea, Tripsacum, Sorghum, and Oryza, in order to gain insight into the long-term evolution of plant defense. The specific objectives of this study were to determine (1) whether wip1 has a history of positive or balancing selection, as has been shown for genes involved in plant defense against pathogens, and (2) if the evolutionary histories of wip1 inhibitory loops, which come into closest contact with proteases, differ from the evolutionary history of other parts of this gene. The Zea polymorphism data are consistent with a neutral evolutionary history. In contrast, relative-rate tests suggest a nonneutral evolutionary history. This inconsistency may indicate that selection acting on wip1 is episodic or that wip1 evolves in response to selection favoring novel alleles. We also detected significant heterogeneity in the evolutionary rates of the two inhibitory loops of wip1-one inhibitory loop is highly conserved, whereas the second has diverged rapidly. Because these two inhibitory loops are predicted to have very similar biochemical functions, the significantly different evolutionary histories suggest that these loops have different ecological functions.

Molecular characterization of Ancylostoma ceylanicum Kunitz-type serine protease inhibitor: evidence for a role in hookworm-associated growth delay

Hookworm infection is a major cause of iron deficiency anemia and malnutrition in developing countries. The Ancylostoma ceylanicum Kunitz-type inhibitor (AceKI) is a 7.9-kDa broad-spectrum inhibitor of trypsin, chymotrypsin, and pancreatic elastase that has previously been isolated from adult hookworms. Site-directed mutagenesis of the predicted P1 inhibitory reactive site amino acid confirmed the role of Met(26) in mediating inhibition of the three target serine proteases. By using reverse transcription-PCR, it was demonstrated that the level of AceKI gene expression increased following activation of third-stage larvae with serum and that the highest level of expression was reached in the adult stage of the parasite. Immunohistochemistry studies performed with polyclonal immunoglobulin G raised against recombinant AceKI showed that the inhibitor localized to the subcuticle of the adult hookworm, suggesting that it has a potential in vivo role in neutralizing intestinal proteases at the surface of the parasite. Immunization with recombinant AceKI was shown to confer partial protection against hookworm-associated growth delay without a measurable effect on anemia. Taken together, the data suggest that AceKI plays a role in the pathogenesis of hookworm-associated malnutrition and growth delay, perhaps through inhibition of nutrient absorption in infected hosts.

Rapid screening for alpha1-antitrypsin deficiency in patients with chronic obstructive pulmonary disease using dried blood specimens

We describe two reliable methods for high-throughput screening of proteinase inhibitor (PI) S and PI Z alpha(1)-antitrypsin (alpha(1)-AT) deficiency alleles from dried blood spot (DBS) specimens using the LightCycler fluorimetric analyzer. The method was used to study 72 patients with chronic obstructive pulmonary disease. Results were confirmed with DNA sequencing. The alpha(1)-AT concentration in DBS was determined with immune nephelometry. Sixteen patients (22%) showed no PI Z or PI S mutations. Five patients (7%) had a heterozygous genotype consisting of a PI S allele and a normal allele for the Z and S positions (non-S non-Z). Twenty-five patients (35%) had a heterozygous genotype consisting of a PI Z and a non-S non-Z allele. Two (3%) had the PI SS genotype, 2 (3%) the PI SZ, and 20 (28%) the PI ZZ. All patients with two normal alpha(1)-AT alleles and 10 heterozygous carriers of one normal and one deficient allele had alpha(1)-AT levels that fell within the alpha(1)-AT DBS normal range (1.8-3.1 mg/dl). Two patients with the rare PI MM(malton)- and PI MM(heerlen)-deficient variants showed deficient alpha(1)-AT levels; PI S and PI Z were not detected. Processing 32 samples requires only 40 minutes. This single-step, cost-effective technology is optimal for working with small amounts of DNA, as are present in DBS. The method is suitable for large-scale screening, in cases where PI type is important.