Amino-acid sequence of porcine pancreatic elastase and its homologies with other serine proteinases

Computational Approach to Identifying New Chemical Entities as Elastase Inhibitors with Potential Antiaging Effects

In the aging process, skin morphology might be affected by wrinkle formation due to the loss of elasticity and resilience of connective tissues linked to the cleavage of elastin by the enzymatic activity of elastase. Little information is available about the structural requirements to efficiently inhibit elastase 1 (EC 3.4.21.36) expressed in skin keratinocytes. In this study, a structure-based approach led to the identification to the pharmacophoric hypotheses that described the main structural requirements for binding to porcine pancreatic elastase as a valuable tool for the development of skin therapeutic agents due to its similarity with human elastase 1. The obtained models were subsequently refined through the application of computational alanine-scanning mutagenesis to evaluate the effect of single residues on the binding affinity and protein stability; in turn, molecular dynamic simulations were carried out; these procedures led to a simplified model bearing few essential features, enabling a reliable collection of chemical features for their interactions with elastase. Then, a virtual screening campaign on the in-house library of synthetic compounds led to the identification of a nonpeptide-based inhibitor (IC50 = 60.4 µM) belonging to the class of N-substituted-1H-benzimidazol-2-yl]thio]acetamides, which might be further exploited to obtain more efficient ligands of elastase for therapeutic applications.

Role of the P2 residue of human alpha 1-antitrypsin in determining target protease specificity

Alpha 1-antitrypsin (A1AT) is a serine protease inhibitor that mainly inhibits neutrophil elastase in the lungs. A variant of A1AT at the P1 position with methionine 358 to arginine (A1AT-Pittsburgh) is a rapid inhibitor of thrombin with greatly diminished anti-elastase activity. The P2 residue (position 357) of A1AT-Pittsburgh has been shown to play an important role in interactions with thrombin and kallikrein, but the role of P2 residue in wild-type A1AT has largely been unraveled. Here, we investigated the effects of P2 proline substitutions in wild-type A1AT on interactions with porcine pancreatic elastase (PPE) and human neutrophil elastase (HNE). The mutant A1AT proteins (P357A, P357D, P357K, P357L, P357N, P357S, and P357W) were less efficient than the wild-type A1AT at inhibiting PPE and HNE. Among the mutants, P357D did not form a complex with PPE, whereas P357L, P357N, and P357W showed significantly reduced complex formation with PPE. Surprisingly, mass spectrometry analysis revealed that P357D had two cleavage sites after the P9 alanine and the P3 isoleucine residues. Our results indicate that the size and negative charge of the R group of the P2 residue influence the interaction with elastases. Specifically, the negative charge at the P2 residue is disfavored and the resulting conformational changes in the reactive center loop upon interaction with PPE lead to cleavage at new sites. Overall, the results of this study demonstrate a previously unknown role for P2 residue in determining inhibitory specificity of A1AT.

Kinetic and computational analysis of the reversible inhibition of porcine pancreatic elastase: a structural and mechanistic approach

Structural and mechanistic insights were revealed for the reversible inhibition of Porcine Pancreatic Elastase (PPE); the kinetics of uninhibited and inhibited hydrolysis of substrate Suc-AAA-pNA was analyzed thoroughly. Additionally, the interactions between PPE and its inhibitor were studied by computational techniques. The uninhibited hydrolysis of Suc-AAA-pNA by PPE proceeds through a virtual transition state, involving an inferior physical and another dominating chemical step, where two stabilized reactant states precede the predominant acyl-enzyme. Different kinds of bonding with the PPE-backbone residues, including those of the catalytic triad, were found during the MD simulation of 5 ns, as key interactions favoring a higher stabilization of the best ranked complex PPE-CF₃C(O)-KA-NHPh-p-CF₃. The proton inventories of the inhibited hydrolysis of Suc-AAA-pNA by PPE, were ruled out the existence of any virtual transition state and thus they argue for a different mode of catalysis involving a structurally disturbed PPE molecule. Thereafter, a novel inhibition mechanism was suggested.

CuInS2 quantum dots as a near-infrared fluorescent probe for detecting thrombin in human serum

This paper describes a novel, simple method for the highly sensitive and selective detection of thrombin using fibrinogen (Fib) and CuInS(2) quantum dots (QDs) as biosensing probes. Water-soluble near-infrared CuInS(2) QDs capped by mercaptopropionic acid (MPA) were directly synthesized by a hydrothermal method. Addition of fibrinogen to the CuInS(2) QDs solution led to the formation of a Fib-CuInS(2) QDs complex through electrostatic interactions and hydrogen bonding, and resulting in the enhancement of photoluminescence (PL) intensity and a red shift of the PL peak. Once thrombin was introduced into the Fib-CuInS(2) QDs system, it catalyzed the polymerization of the free and conjugated fibrinogen species to form insoluble fibrillar fibrin-CuInS(2) QDs agglutinates. After centrifugation, the PL intensity of the supernatants decreased upon increasing the concentration of thrombin. This Fib-CuInS(2) QDs probe provided a highly specific selectivity and a linear detection of thrombin in the range of 6.7 × 10(-11) to 3.9 × 10(-7) mol L(-1) with a detection limit (LOD) of about 8.7 × 10(-12) mol L(-1), and realized the thrombin detection in human serum samples directly. Compared with those obtained by using other nanomaterials and aptamer-based detection methods, this approach provided a lower LOD for thrombin detection. The proposed approach provides a simple and fast-responding procedure, which might hold a promising potential for application in the diagnosis of diseases associated with coagulation abnormalities and cancers.

Organosoluble enzyme conjugates with poly(2-oxazoline)s via pyromellitic acid dianhydride

The use of enzymes in organic solvents offers a great opportunity for the synthesis of complex organic compounds and is therefore in focus of current research. In this work we describe the synthesis of poly(2-methyl-1,3-oxazoline) (PMOx) and poly(2-ethyl-1,3-oxazoline) (PEtOx) enzyme conjugates with hen-egg white lysozyme, RNase A and α-chymotrypsin using a new coupling technique. The POXylation was carried out reacting pyromellitic acid dianhydride subsequently with ethylenediamine terminated POx and then with the NH₂-groups of the respective enzymes. Upon conjugation with the polymers, RNase A and lysozyme became fully soluble in DMF (1.4 mg/ml). These are the first examples of fully POXylated proteins, which become organosoluble. The synthesized enzyme conjugates were characterized by SDS-PAGE, isoelectric focusing, dynamic light scattering and size exclusion chromatography, which all indicated the full POXylation of the enzymes. The modified enzymes even partly retained their activity in water. With α-chymotrypsin as example we could demonstrate that the molecular weight of the attached polymer significantly influences the activity.

The catalytic aspartate is protonated in the Michaelis complex formed between trypsin and an in vitro evolved substrate-like inhibitor: a refined mechanism of serine protease action

The mechanism of serine proteases prominently illustrates how charged amino acid residues and proton transfer events facilitate enzyme catalysis. Here we present an ultrahigh resolution (0.93 Å) x-ray structure of a complex formed between trypsin and a canonical inhibitor acting through a substrate-like mechanism. The electron density indicates the protonation state of all catalytic residues where the catalytic histidine is, as expected, in its neutral state prior to the acylation step by the catalytic serine. The carboxyl group of the catalytic aspartate displays an asymmetric electron density so that the O_δ2–C_γ bond appears to be a double bond, with O_δ2 involved in a hydrogen bond to His-57 and Ser-214. Only when Asp-102 is protonated on O_δ1 atom could a density functional theory simulation reproduce the observed electron density. The presence of a putative hydrogen atom is also confirmed by a residual mF_obs − DF_calc density above 2.5 σ next to O_δ1. As a possible functional role for the neutral aspartate in the active site, we propose that in the substrate-bound form, the neutral aspartate residue helps to keep the pK_a of the histidine sufficiently low, in the active neutral form. When the histidine receives a proton during the catalytic cycle, the aspartate becomes simultaneously negatively charged, providing additional stabilization for the protonated histidine and indirectly to the tetrahedral intermediate. This novel proposal unifies the seemingly conflicting experimental observations, which were previously seen as either supporting the charge relay mechanism or the neutral pK_a histidine theory.

Natural occurring polyphenols as template for drug design. Focus on serine proteases

Several major physio-pathological processes, including cancer, inflammatory states and thrombosis, are all strongly dependent upon the fine regulation of proteolytic enzyme activities, and dramatic are the consequences of unbalanced equilibria between enzymes and their cognate inhibitors. In this perspective, the discovery of small-molecule ligands able to modulate catalytic activities has a massive therapeutic potential and is a stimulating goal. Numerous recent experimental evidences revealed that proteolytic enzymes can be opportunely targeted, reporting on small ligands capable of binding to these biological macromolecules with drug-like potencies, and primarily with comparable (or even higher) efficiency with respect to their endogenous binding partner. In particular, natural occurring polyphenols and their derivatives recently disclosed these intriguing abilities, making them promising templates for drug design and development. In this review, we compared the inhibitory capacities of a set of monomeric polyphenols toward serine proteases activity, and finally summarized the data with an emphasis on the derivation of a pharmacophore model.

Activation mechanisms of coagulation factor IX

Blood haemostasis is accomplished by a complex network of coagulatory and fibrinolytic processes. These processes have to be delicately balanced, as clinically manifested by bleeding disorders, such as haemophilia A and B. These disorders are caused by defects in coagulation factor VIII and factor IX, respectively. Following a dual strategy, we emphasise on the one hand principles conserved in most coagulation enzymes, thus mirroring much of the underlying complexity in haemostasis; on the other hand, we identify enzymatic properties of the factor IXa-factor VIIIa system (Xase) that distinguish this proteolytic machine from other components of the coagulation system. While the exact mechanisms of its activity modulation remain baffling until today, superactive factor IX mutants significantly improve our current understanding and serve as a specific and testable model of Xase action.

The primary structure of human urogastrone

Urogastrone is a potent inhibitor of gastric acid secretion which is present in human urine. Its existence has been known for over 30 years but it has only recently been isolated in a sufficiently pure form for detailed structural studies to be undertaken. Two separate polypeptides beta- and gamma-urogastrone were isolated. The structures were established by carrying out enzymic degradations of S-carboxymethyl and S-carboxamidomethyl derivatives with trypsin, chymotrypsin, thermolysin and a protease derived from the fungus Armillaria mellea. Sequences of the smaller peptides thus obtained were determined by the dansyl Edman method. Partial acid hydrolysis of urogastrone itself gave fragments containing single intact disulphide bonds, and oxidation then allowed the direction of individual bonds to be established. Beta-Urogastrone was shown to be a 53-amino acid residue polypeptide containing three disulphide bonds, and gamma-urogastrone had an identical sequence but lacked the C-terminal arginine residue. Urogastrone was subsequently found to be structurally related to mouse epidermal growth factor in that 37 of the 53 residues were commonly located in each polypeptide. Furthermore, as both peptides has similar effects upon gastric acid secretion and upon epidermal growth, urogastrone was also a human epidermal growth factor. The 16 variable residues were spread across the molecule, all apart from two were compatible with single base changes in the triplet condons, and the overall effect was to make uorgastrone more acidic than EGF. The smallest biologically active unit has not been defined but at least six residues can be removed from the C-terminus without causing a reduction in potency.

Nonspecific cytotoxic cells of teleosts are armed with multiple granzymes and other components of the granule exocytosis pathway

Granzymes are members of the serine protease family and major components of cytotoxic granules of professional killer cells. Multiple granzymes have been identified from human and rodents with different substrate specificities. Although the significance of granzymes A and B in cell-mediated cytotoxicity has been extensively investigated, recent reports suggest that other granzymes may have either equal or greater importance in mediating cell death. Studies on the evolution of these closely related proteases were hindered by the lack of sequence and biochemical information of granzymes from "lower vertebrates." Here we report the generation of a catalytically active recombinant granzyme identified in the cytotoxic cells of an ectothermic vertebrate. Fully active, soluble recombinant catfish granzyme-1 (CFGR-1) was generated using a yeast-based expression system. In vitro enzyme kinetic assays using various thiobenzyl ester substrates verified its tryptase activity in full agreement with previous observations by sequence comparison and molecular modeling. The tryptase activity that was secreted from catfish NCC during an in vitro cytotoxicity assay strongly correlated with the cytotoxicity induced by these cells. Evidence for additional granzymes with different substrate specificities in NCC was obtained by analysis of the protease activity of supernatants collected from in vitro cytotoxicity assays. Searches of the catfish EST database further confirmed the presence of teleost granzymes with different substrate specificities. Granzyme activity measurements suggested a predominance of chymase and tryptase activities in NCC. Further proof that the granule exocytosis pathway is one of the cytotoxic mechanisms in NCC was provided by the expression of granule components perforin, granulysin and serglycin detected by RT-PCR analysis. These results demonstrate the evidence for a parallel evolution of effector molecules of cell-mediated cytotoxicity in teleosts.

Cloning and expression of ostrich trypsinogen: an avian trypsin with a highly sensitive autolysis site

One of ostrich (Struthio camelus) trypsinogen genes was cloned from pancreatic cDNA. Its amino acid sequence compared to known trypsin sequences from other species shows high identity and suggests that it is a member of the phylogenetically anionic trypsinogen I subfamily. After cytoplasmic over expression in Escherichia coli and renaturation, the activation properties of ostrich trypsinogen were studied and compared to those of human trypsinogen 1 (also called as human cationic trypsinogen). Ostrich trypsinogen undergoes bovine enterokinase activation and autoactivation much faster than human trypsinogen 1 and exhibits on a synthetic substrate a somewhat higher enzymatic activity than the latter one. The most interesting property of ostrich trypsin is its relatively fast autolysis that can be explained via a mechanism different from the common mechanism for rat and human 1 trypsins. The latter proteases have a site, Arg117-Val118, where the autolysis starts and then goes on in a zipper-like fashion. This is absent from ostrich trypsin. Instead it has a couple of cleavage sites within regions 67-98, including two unusual ones, Arg76-Glu77 and Arg83-Ser84. These appear to be hydrolysed fast in a non-consecutive manner. Such an autolysis mechanism could not be inhibited by a single-site mutation which in humans is proposed to lead to pancreatitis.

A despecialization step underlying evolution of a family of serine proteases

In the trypsin superfamily of serine proteases, non-trypsin-like primary specificities have arisen in only two monophyletic descendent subbranches. We have recreated an ancestor to one of these subbranches (granzyme) using phylogenetic inference, gene synthesis, and protein expression. This ancestor has two unusual properties. First, it has broad primary specificity encompassing the entire repertoire of novel primary specificities found in its descendents. Second, unlike extant members that have narrow primary specificities, the ancestor exhibits tolerance to mutational changes in primary specificity-conferring residues-that is, structural plasticity. Molecular modeling and mutagenesis studies indicate that these unusual properties are due to a particularly wide substrate binding pocket. These two crucial properties of the ancestor not only distinguish it from its extant descendents but also from the trypsin-like proteases that preceded it. This indicates that a despecialization step, characterized by broad specificity and structural plasticity, underlies evolution of new primary specificities in this protease superfamily.

Pancreatic elastase is proven to be a mannose-binding protein--implications for the systemic response to pancreatitis

BACKGROUND

Mannose-binding proteins (MBPs) have been isolated from serum, liver, lung, and kidney and are believed to play an important role in first-line host defense during acute phase inflammatory response. Because of the inflammatory nature of pancreatitis, we postulate that the pancreas produces endogenous MBP.

METHODS

Pancreatic juice, from both human and rat, was collected by pancreatic duct cannulation and subjected to mannose-Sepharose affinity chromatography to isolate pancreatic MBP (pMBP). Protein eluates from the mannose-Sepharose column were analyzed using reverse-phase high-performance liquid chromatography, sodium dodeclysulfate-polyacrylamide gel electrophoresis, and, subsequently, by N-terminal protein sequencing. Western blot analysis was used to identify the pMBP, and reverse transcriptionase-polymerase chain reaction was used to examine its mRNA expression. Complement lysis was measured using red blood cells coated with yeast mannan. Tumor necrosis factor (TNF)-alpha mRNA expression in macrophages was measured using RNase protection assay.

RESULTS

A 30-kd MBP was isolated from both human and rat pancreatic juice and a rat acinar cell line. Genetic analysis (using RT-PCR with known MBP primers) and protein analysis (using Western blot with a known anti-MBP antibody) suggest that the pMBP is different from any previously described MBP. Protein sequencing analysis of pMBP generated an N-terminus sequence of 12 residues, indicating that pMBP is human pancreatic elastase III. Western blot analysis using an anti-elastase antibody confirms that the pMBP is a pancreatic elastase. Exposure of macrophages to pancreatic elastase resulted in an increased mRNA level of TNF-alpha, a potent proinflammatory cytokine in acute-phase response. Addition of mannan to pancreatic elastase further upregulated the TNF-alpha response.

CONCLUSION

We isolated an MBP from the pancreas and identified it as pancreatic elastase. We characterized it as having properties different from that of any previously known MBP. We showed that pMBP or pancreatic elastase is involved in the activation of macrophages, and that this activation is potentiated by mannan. We postulate that the mannose-binding properties of pancreatic elastase identify this enzyme as a candidate catalyst for both pancreatic and systemic inflammation.

Crystal structure reveals basis for the inhibitor resistance of human brain trypsin

Severe neurodegradative brain diseases, like Alzheimer, are tightly linked with proteolytic activity in the human brain. Proteinases expressed in the brain, such as human trypsin IV, are likely to be involved in the pathomechanism of these diseases. The observation of amyloid formed in the brain of transgenic mice expressing human trypsin IV supports this hypothesis. Human trypsin IV is also resistant towards all studied naturally occurring polypeptide inhibitors. It has been postulated that the substitution of Gly193 to arginine is responsible for this inhibitor resistance. Here we report the X-ray structure of human trypsin IV in complex with the inhibitor benzamidine at 1.7 A resolution. The overall fold of human trypsin IV is similar to human trypsin I, with a root-mean square deviation of only 0.5 A for all C(alpha) positions. The crystal structure reveals the orientation of the side-chain of Arg193, which occupies an extended conformation and fills the S2' subsite. An analysis of surface electrostatic potentials shows an unusually strong clustering of positive charges around the primary specificity pocket, to which the side-chain of Arg193 also contributes. These unique features of the crystal structure provide a structural basis for the enhanced inhibitor resistance, and enhanced substrate restriction, of human trypsin IV.

Determination of pancreas injury from bloodstains using human pancreatic elastase III as a marker

A sensitive sandwich enzyme immunoassay for human pancreatic elastase III as a method to identify pancreas injuries from blood or bloodstains was evaluated. The serum levels of human elastase III from healthy adults (n=24) were estimated to be 1.15 +/- 0.6 (+/- SD) ng/ml. The recovery rates of elastase III added to normal human serum were estimated to be 96.3%. Elastase III levels in contents of various digestive organs were assayed and found to be high in the contents of the large intestine. For detection of human elastase III on weapons, samples were prepared from disposable scalpels that had been used to cut skin and skeletal muscle, and then to cut various organs. The mean ratio of elastase III to total protein (ng elastase III/mg protein) on scalpels that had been cut the pancreas (n=11) was 4956+/-3067 (+/- SD), whereas the ratios from other organs were much lower except, in case of several digestive organs. The higher elastase III levels detected in these digestive organs seemed to stem from the amount of intestinal contents adhering to the scalpels. These results suggest that determination of pancreatic elastase III in blood or bloodstains using a sandwich enzyme immunoassay is a very useful and effective tool for identification of pancreas injury in forensic practice.

Role of protein-solvent interactions in refolding: effects of cosolvent additives on the renaturation of porcine pancreatic elastase at various pHs

The effects of cosolvent additives on the refolding of porcine pancreatic elastase were studied by comparing the enzymatic activity and the conformation of the enzyme renatured at various pHs with those of the native elastase under the same cosolvent and pH conditions. A lag period was observed before reaching the steady state of the hydrolysis of an amide substrate, and the lag period measured with the refolding enzyme was longer than that measured with the native elastase. Depending on the cosolvent studied (acetonitrile, dimethylsulfoxide, glycerol, methanol) there was or was not a dramatic increase in the duration of the lag period measured with the refolding enzyme, but not in the case of the native elastase. These results and additional kinetic data on inactivation of the enzyme demonstrated that dimethylsulfoxide, glycerol, and methanol enhance the stability of the intermediates able to refold into the native form, contrary to acetonitrile. In neither the case of the native enzyme nor that of the renatured enzyme, did the cosolvents modify the pK(app) of ionization of the amino acids that control enzymatic activity, indicating that they did not penetrate the core of the refolded elastase. Conversely, they shifted toward a more alkaline pH the structural transition of the native elastase, and the amplitude of the shift was comparable to that observed in bulk water with elastase whose Ser 195 has been acylated, suggesting that cosolvents stabilized the structure of the folded molecule by increasing its packing.

Bovine pancreatic preproelastases I and II: comparison of nucleotide and amino acid sequences and tissue specific expression

Clones encoding bovine preproelastases I and II were isolated from a pancreatic cDNA library and were sequenced in order to define the structural characteristics of these enzymes. The bovine 947- and 884-nucleotide preproelastase I and II cDNAs encode proteins containing a signal peptide of the same length (16 amino acids), but with a slightly different number of amino acids for the activation peptide (10 and 12, respectively) and the mature enzyme (240 and 241, respectively). Considering amino acid sequences, each enzyme shares a high degree of identity (76-86%) within species. In contrast, only 55.3% identity is found between bovine elastases I and II. This difference could explain partly their own specificity. Analysis of the expression of the elastases in various bovine tissues demonstrated that they are specifically expressed in high levels in the pancreatic gland. These two approaches (structure and expression) allowed us to characterize the bovine pancreatic elastases I and II.

Macrophage-derived metalloelastase is responsible for the generation of angiostatin in Lewis lung carcinoma

To determine the mechanism responsible for the in vivo production of angiostatin that inhibits growth and metastasis in Lewis lung carcinoma (3LL), we implanted 3LL variant cells into the subcutis of syngeneic C57BL/6 mice. The tumors were infiltrated by macrophages and expressed high levels of steady-state mRNA for metalloelastase (MME). Successive passages (more than three) of cultures established from the tumors resulted in complete depletion of macrophages; steady-state MME mRNA, elastinolytic activity, and production of angiostatin (in the presence of plasminogen) were correspondingly reduced. Coculture of macrophages with either 3LL cells or their conditioned media containing granulocyte-macrophage colony-stimulating factor resulted in secretion of MME and production of angiostatin by the macrophages, suggesting that angiostatin is produced by tumor-infiltrating macrophages whose MME expression is stimulated by tumor cell-derived granulocyte-macrophage colony-stimulating factor.

Isolation and characterization of two cDNAs from Atlantic cod encoding two distinct psychrophilic elastases

The cDNAs encoding two different Atlantic cod elastases have been isolated and sequenced. The predicted amino acid sequences revealed two preproelastases, consisting of a signal peptide, an activation peptide and a mature enzyme of 242 and 239 amino acids. Amino acid sequence identity between the two cod elastases was 60.1% and identity with mammalian elastases ranged from 50-64%. The two cod elastases contain all the major structural features common to serine proteases, such as the catalytic triad His57, Asp102 and Ser195. Both cod elastases have a high content of methionine, consistent with previous findings in psychrophilic fish enzymes.

Elastase enhances cAMP accumulation and the inhibition of DNA synthesis induced by OP-41483, a stable prostacyclin analogue, in vascular smooth muscle cells

To define the physiological roles of elastase in the vascular wall, we examined whether elastase at low concentrations can modulate the proliferation of vascular smooth muscle cells (VSMC). Elastase itself at low concentrations from 1 to 50 ng/ml inhibited DNA synthesis dose-dependently in VSMC. However, phenylmethylsulfonyl fluoride-inactivated elastase failed to induce this inhibition. OP-41483, a stable analogue of prostacyclin, inhibited DNA synthesis and stimulated accumulation of cAMP in VSMC. Preincubation of VSMC for 24 h with 50 ng/ml elastase enhanced both inhibition of DNA synthesis and the accumulation of cAMP induced by OP-41483. Preincubation of VSMC with 12-O-tetradecanoylphorbol 13-acetate, an activator of protein kinase C (PKC), also enhanced cAMP accumulation induced by OP-41483. On the other hand, elastase failed to enhance OP-41483-induced cAMP accumulation in PKC down-regulated cells. Furthermore, coincubation with chelerythrine, an inhibitor of PKC, inhibited the enhancement of cAMP accumulation induced by preincubation with elastase. These results suggest that elastase at low concentrations can enhance the inhibition of VSMC proliferation induced by prostacyclin through the activation of protein kinase C.

67-kD elastin-binding protein is a protective "companion" of extracellular insoluble elastin and intracellular tropoelastin

The 67-kD elastin-binding protein (EBP) mediates cell adhesion to elastin and elastin fiber assembly, and it is similar, if not identical, to the 67-kD enzymatically inactive, alternatively spliced beta-galactosidase. The latter contains an elastin binding domain (S-GAL) homologous both to the aorta EBP and to NH2-terminal sequences of serine proteinases (Hinek, A., M. Rabinovitch, F. W. Keeley, and J. Callahan. 1993. J. Clin. Invest. 91:1198-1205). We now confirm the functional importance of this homology by showing that elastolytic activity of a representative serine elastase, porcine pancreatic elastase, was prevented by an antibody (anti-S-GAL) and by competing with purified EBP or S-GAL peptide. Immunohistochemistry of adult aorta indicates that the EBP exists as a permanent component of mature elastic fibers. This observation, together with the in vitro studies, suggests that the EBP could protect insoluble elastin from extracellular proteolysis and contribute to the extraordinary stability of this protein. Double immunolabeling of fetal lamb aorta with anti-S-GAL and antitropoelastin antibodies demonstrated, under light and electron microscopy, intracellular colocalization of the proteins in smooth muscle cells (SMC). Incubation of SMC with galactosugars to dissociate tropoelastin from EBP caused intracellular aggregation of tropoelastin. A tropoelastin/EBP complex was extracted from SMC lysates by coimmunoprecipitation and cross-linking, and its functional significance was addressed by showing that its dissociation by galactosugars caused degradation of tropoelastin by endogenous serine proteinase(s). This suggests that the EBP may also serve as a "companion" to intracellular tropoelastin, protecting this highly hydrophobic protein from self-aggregation and proteolytic degradation.

Nucleotide sequence of a novel arylesterase gene from Vibro mimicus and characterization of the enzyme expressed in Escherichia coli

A gene coding for an arylesterase of Vibrio mimicus was cloned. Sequence determination reveals that the esterase gene has an open reading frame of 600 nucleotides which encodes a protein of M(r) 22,300. The deduced amino acid sequence contain a pentapeptide GDSLS (residues 27-31), which was also found in the phospholipid-cholesterol acyltransferase from Aeromonas hydrophila. Substitution of Ser-29 by alanine or cysteine in the cloned gene abolished the esterase activity in the tributyrin plate assay. On the other hand, the activity was not lost when Ser-31 was changed to alanine. The cloned gene was expressed in Escherichia coli, and the protein purified by a four-step procedure. The purified protein migrated on SDS/PAGE as a single band with an apparent M(r) of 22,100. This enzyme favoured the hydrolysis of several arylesters and was classified as an arylesterase (EC 3.1.1.2). N-Terminal analysis showed that Ser-20 was the first amino acid of the mature secreted protein, suggesting that the N-terminal 19 hydrophobic amino acids served as a signal peptide.

A molecular model of the serine protease domain of activated protein C: application to the study of missense mutations causing protein C deficiency

A molecular model of the serine protease domain of protein C was constructed by standard comparative methods. Individual missense mutations were inserted into the model and plausible explanations for their interference with protein C structure/function were derived through consideration of location, steric effects and protein stability. A hydrophilic cluster of many Arg and Lys residues, found adjacent to the active site cleft, is proposed to be involved in thrombomodulin and/or protein S interactions. Analysis of comparative binding studies also suggested the presence of an extended substrate binding pocket in the model.

Amino acid sequence of alkaliphilic serine protease from silkworm, Bombyx mori, larval digestive juice

Alkaliphilic protease, P-IIc, from silkworm, Bombyx mori, larval midgut digestive juice consists of 232 amino acids. It has a catalytic triad, Asp-His-Ser, invariably found in a serine protease. A shift of optimal pH value towards the alkaline side diminished at mu = 1.0. This suggests the existence of an electrostatic interaction that affects the proteolytic activity. The higher Arg content may be responsible for this phenomenon. Two cysteine residues probably exist unpaired in a novel position among serine proteases.

The 67-kD elastin/laminin-binding protein is related to an enzymatically inactive, alternatively spliced form of beta-galactosidase

We and others have previously shown that a 67-kD cell surface elastin/laminin-binding protein (EBP) is responsible for cell adhesion to elastin and laminin and for mediating the process of elastin fiber assembly, but the nature of this protein was unknown. In this report we provide evidence that a 67-kD catalytically inactive form of beta-galactosidase produced by alternative splicing demonstrates immunological and functional similarity and sequence homology to the 67-kD EBP, suggesting that the two might be the same. Antibody prepared to a synthetic peptide, N-Ac-GSPSAQDEASPL, corresponding to a frame-shift-generated sequence unique to the alternatively spliced form of human beta-galactosidase, also recognized sheep EBP both on Western blotting and in aortic tissue. Furthermore, this synthetic peptide (S-GAL) binds to elastin and laminin, but not to fibronectin, collagen I, or collagen III. Moreover, both tropoelastin and laminin which bind to S-GAL peptide affinity columns can be specifically eluted from them with an excess of free S-GAL peptides. In addition, sequence homology among this splice variant of human beta-galactosidase, sheep EBP, and NH2-terminal sequences of some elastases suggests that these proteins share a common ligand-binding motif that has not been previously recognized.

Inhibition of Aspergillus fumigatus elastase with monoclonal antibodies produced by using denatured elastase as an immunogen

In preparing monoclonal antibodies to the elastase from Aspergillus fumigatus, we found that the enzyme was weakly immunogenic in BALB/c mice. Antiserum titers were only 1:1,000 to 1:5,000, and hybridomas secreted nonspecific immunoglobulin M (IgM). Denaturing the elastase in 0.5% sodium dodecyl sulfate at 80 degrees C for 10 min prior to injection increased titers of antiserum against the nondenatured (native) enzyme 10-fold. Of eight hybridomas selected following immunization with the denatured enzyme, seven produced IgG reactive with the native enzyme and one produced nonspecific IgM. The nondenatured immunogen tested again yielded mainly IgM producers. Immunoblots and enzyme-linked immunosorbent assay showed that the IgG monoclonal antibodies were reactive with both the denatured and nondenatured fungal elastases; none cross-reacted with human neutrophil elastase, porcine pancreatic elastase, or Pseudomonas elastase. Elastase-specific polyclonal antibody produced in mice inhibited elastase activity beginning at a molar ratio (antibody to elastase) of 4:1, and activity was completely inhibited at 14.5:1. Some individual monoclonal antibodies partially inhibited elastase, but certain pairs, at a molar ratio of each antibody to elastase of 5.4:1, acted synergistically to inhibit the activity completely.

Primary structure of rat pancreatic lipase mRNA

The sequence of rat pancreatic lipase mRNA was determined. The data have been assigned the following accession number, X61925, in the EMBL data library. The total length of the messenger is 1531 nucleotides, plus a poly(A) stretch of about 60 nucleotides. A 72-nucleotides 5'-noncoding region is followed by a 1419-nucleotides open reading frame which encodes a protein of 473 amino acids, including the 17 amino acid signal peptide. The mature enzyme (456 residues) has 6 additional C-terminal amino acids, as compared with the amino acid sequence of pig (direct amino acid sequence), dog, man and rat isoenzyme from Genbank, M58369 (all deduced from the nucleotide sequence). A higher degree of homology exists between the amino acid sequence of rat mature enzyme with those of dog (88%), pig (75%) and man (75%) than with that of rat isolipase (74%).

The amino-terminal sequence of the catalytic subunit of bovine enterokinase

Bovine enterokinase (enteropeptidase) is a serine protease and functions as the physiological activator of trypsinogen. The enzyme has a heavy chain (115 kD) covalently linked to a light or catalytic subunit (35 kD). The amino acid composition showed that the light chain has nine half-cystine residues (four as intramolecular disulfides) and that one half-cystine was in a disulfide link between the light and heavy subunits. The amino-terminal 27 residues of the S-vinylpyridyl derivative of the light chain were determined by gas-phase Edman degradation. The sequence has homologies with other serine proteases containing one or two chains. The homologies suggest that the catalytic subunit has the same three-dimensional structure and, therefore, the same mechanism of enzymatic action as pancreatic chymotrypsin, trypsin, and elastase. The presence of the conserved amino-terminal activation peptide sequence (IVGG) shows that enterokinase must have a zymogen precursor and that the two-chain enzyme arises from limited proteolysis during posttranslational processing.

Nonenzymatic deamidation of asparaginyl and glutaminyl residues in proteins

Some asparagine and glutamine residues in proteins undergo deamidation to aspartate and glutamate with rates that depend upon the sequence and higher-order structure of the protein. Functional groups within the protein can catalyze this reaction, acting as general acids, bases, or stabilizers of the transition state. Information from specific proteins that deamidate and analysis of protein sequence and structure data bases suggest that asparagine and glutamine lability has been a selective pressure in the evolution of protein sequence and folding. Asparagine and glutamine deamidation can affect protein structure and function in natural and engineered mutant sequences, and may play a role in the regulation of protein folding, protein breakdown, and aging.

Rat pancreatic colipase mRNA: nucleotide sequence of a cDNA clone and nutritional regulation by a lipidic diet

A cDNA clone encoding rat pancreatic colipase was isolated using as a probe a synthetic deoxyoligonucleotide corresponding to a highly conserved amino acid sequence region in colipases from other species. The cloned messenger codes for a protein of 95 amino acids plus a signal peptide of 17 amino acids. The structure of the full-length cDNA was also determined and the corresponding amino acid sequence showed a high degree of homology with those of other known colipases. Quantification of the homologous mRNA in the pancreas of animals fed a high-lipid diet was consistent with a specific though moderate induction of colipase messenger by the nutritional manipulation.

Purification and characterization of pancreatic elastase from Atlantic cod (Gadus morhua)

1. A pancreatic elastase from Atlantic cod (Gadus morhua) has been purified and characterized. 2. The enzyme is a very basic protein with an approximate mol. wt of 28,000. 3. The cod elastase has higher elastin specificity than porcine elastase, and it is inhibited by soybean trypsin inhibitor, which has no effect on porcine elastase. 4. The cod elastase expresses a higher turnover number (kcat) and catalytic efficiency (kcat/Km) than porcine elastase, but it is less thermostable.

A comparison of the antioxidant requirements of proteins with those of synthetic polymers suggests an antioxidant function for clusters of aromatic and bivalent sulphur-containing amino acid residues

Many proteins which function in extracellular environments potentially rich in oxygen-derived free radicals contain clustered tyrosine and cysteine residues which, by analogy with the chemistry of antioxidants used with synthetic polymers, may provide an appreciable antioxidant and redox stabilization activity. Such proteins may function as antioxidants, and as ligand binding sites for free radicals and other active molecules employed in normal biochemical processes.

Amino acid analysis: determination of cysteine plus half-cystine in proteins after hydrochloric acid hydrolysis with a disulfide compound as additive

All cysteine and cystine in a protein are derivatized during hydrolysis in hydrochloric acid containing 3,3'-dithiodipropionic acid. The resulting derivative can be separated from other amino acids and used for quantitation of cysteine plus half-cystine. A procedure is presented for accurate determination by ion exchange chromatography and postcolumn derivatization of all amino acids from acid hydrolysis of a protein, including the Cys-derivative.

Anhydroelastase: enhanced affinity toward product-type ligands revealed by affinity chromatography

Anhydroelastase was effectively isolated by a single operation of affinity chromatography from a complex mixture produced by phenylmethylsulfonylation and alkaline treatment of porcine pancreatic elastase. The adsorbent used for the chromatography was 6-aminohexanoyl-trialanine, which corresponds to a product of elastase action, immobilized on Sepharose 4B. Successful resolution by the operation indicated that this immobilized ligand possesses the highest affinity for anhydroelastase among various proteins including regenerated elastase in the mixture. Comparative affinity chromatography on immobilized anhydroelastase and on immobilized native elastase further confirmed the stronger interaction of anhydroelastase with the product-type peptides. Immobilized anhydroelastase was also found to be useful in the purification and search for naturally occurring proteinase inhibitors.

Characterization of pancreatic elastase II cDNAs: two elastase II mRNAs are expressed in human pancreas

The primary structures of porcine and human pancreatic elastase II precursors were elucidated by molecular cloning and cDNA sequence analysis. The sequences of the cDNAs cloned from a human pancreatic cDNA library indicate that at least two elastases II are expressed in this tissue. These two human elastases II have been designated elastases IIA and IIB. All the cDNA sequences obtained, including porcine elastase II cDNA, reveal that elastase II is synthesized as a preproenzyme of 269 amino acids, including a predicted signal peptide of 16 amino acids and a predicted activation peptide of 12 amino acids. Human elastase IIA contains the published amino-terminal sequence (16 residues) for human pancreatic proelastase II, whereas elastase IIB shares 50% homology with the published 16-residue sequence. However, there is 90% homology between the overall amino acid sequences of elastases IIA and IIB. Blot hybridization analysis of the poly-adenylated RNAs isolated from various human tissues demonstrates that the human elastase II mRNAs are specifically detected in the pancreas.

Primary structure of human neutrophil elastase

The complete amino acid sequence of human neutrophil elastase has been determined. The protein consists of 218 amino acid residues, contains two asparagine-linked carbohydrate side chains, and is joined together by four disulfide bonds. Comparison of the sequence to other serine proteinases indicates only moderate homology with porcine pancreatic elastase (43.0%) or neutrophil cathepsin G (37.2%). In particular, many of the residues suggested to play important roles in the mechanism by which the pancreatic elastase functions are significantly changed in the neutrophil enzyme, indicating alternative types of binding with the human proteinase.

New scoring matrix for amino acid residue exchanges based on residue characteristic physical parameters

Based on residue characteristic physical parameters, a new scoring matrix, called EMPAR, for amino acid exchanges in proteins was obtained. When comparing protein sequences for detecting homologies, the use of this matrix in place of the Dayhoff log-odds matrix yields results that reflect the topological similarities in the proteins. The use of EMPAR is equivalent to the parametric correlates coefficient approach of Ooi and his colleagues. This matrix correlates at 0.63 with the Dayhoff matrix.