Increasing the thermal stability of euphauserase. A cold-active and multifunctional serine protease from Antarctic krill

Characterization and activity-folding relationship of serine protease from Antarctic krill (Euphausia superba)

Euphausia superba (Antarctic krill) serine protease (ESP) was investigated to gain insights into the activity-structural relationship, folding behavior, and regulation of the catalytic function. We purified ESP from the krill muscle and characterized biochemical distinctions via enzyme kinetics. Studies of inhibition kinetics and unfolding in the presence of a serine residue modifier, such as phenylmethanesulfonyl fluoride, were conducted. Structural characterizations were measured by spectrofluorimetry, including 1-anilinonaphthalene-8-sulfonate dye labeling for hydrophobic residues. The computational simulations such as docking and molecular dynamics were finally conducted to detect key residues and folding behaviors in a nano-second range. The kinetic parameters of ESP were measured as K_m^BANH = 0.97 ± 0.15 mM and k_cat/K_m^BANH = 4.59 s^-1/mM. The time-interval kinetics measurements indicated that ESP inactivation was transformed from a monophase to a biphase process to form a thermodynamically stable state. Spectrofluorimetry measurements showed that serine is directly connected to the regional folding of ESP. Several osmolytes such as proline and glycine only partially protected the inactive form of ESP by serine modification. Computational molecular dynamics and docking simulations showed that three serine residues (Ser183, Ser188, and Ser207) and Cys184, Val206, and Gly209 are key residues of catalytic functions. Our study revealed the functional roles of serine residues as key residues of catalytic function at the active site and of the structural conformation as key folding factors, where ESP displays a flexible property of active site pocket compared to the overall structure.Communicated by Ramaswamy H. Sarma.

Biochemical Study of Fibrinolytic Protease from Euphausia superba Possessing Multifunctional Serine Protease Activity

BACKGROUND

Fibrinolytic protease from Euphausia superba (EFP) was isolated.

OBJECTIVE

Biochemical distinctions, regulation of the catalytic function, and the key residues of EFP were investigated.

METHODS

The serial inhibition kinetic evaluations coupled with measurements of fluorescence spectra in the presence of 4-(2-aminoethyl) benzene sulfonyl fluoride hydrochloride (AEBSF) was conducted. The computational molecular dynamics (MD) simulations were also applied for a comparative study.

RESULTS

The enzyme behaved as a monomeric protein with a molecular mass of about 28.6 kD with K_m ^BApNA = 0.629 ± 0.02 mM and k_cat/K_m ^BApNA = 7.08 s-1/mM. The real-time interval measurements revealed that the inactivation was a first-order reaction, with the kinetic processes shifting from a monophase to a biphase. Measurements of fluorescence spectra showed that serine residue modification by AEBSF directly caused conspicuous changes of the tertiary structures and exposed hydrophobic surfaces. Some osmolytes were applied to find protective roles. These results confirmed that the active region of EFP is more flexible than the overall enzyme molecule and serine, as the key residue, is associated with the regional unfolding of EFP in addition to its catalytic role. The MD simulations were supportive to the kinetics data.

CONCLUSION

Our study indicated that EFP has an essential serine residue for its catalyst function and associated folding behaviors. Also, the functional role of osmolytes such as proline and glycine that may play a role in defense mechanisms from environmental adaptation in a krill's body was suggested.

Crustacean Proteases and Their Application in Debridement

Digestive proteases from marine organisms have been poorly applied to biomedicine. Exceptions are trypsin and other digestive proteases from a few cold-adapted or temperate fish and crustacean species. These enzymes are more efficient than enzymes from microorganism and higher vertebrates that have been used traditionally. However, the biomedical potential of digestive proteases from warm environment species has received less research attention. This review aims to provide an overview of this unrealised biomedical potential, using the debridement application as a paradigm. Debridement is intended to remove nonviable, necrotic and contaminated tissue, as well as fibrin clots, and is a key step in wound treatment. We discuss the physiological role of enzymes in wound healing, the use of exogenous enzymes in debridement, and the limitations of cold-adapted enzymes such as their poor thermal stability. We show that digestive proteases from tropical crustaceans may have advantages over their cold-adapted counterparts for this and similar uses. Differences in thermal stability, auto-proteolytic stability, and susceptibility to proteinase inhibitors are discussed. Furthermore, it is proposed that the feeding behaviour of the source organism may direct the evaluation of enzymes for particular applications, as digestive proteases have evolved to fill a wide variety of feeding habitats, natural substrates, and environmental conditions. We encourage more research on the biomedical application of digestive enzymes from tropical marine crustaceans.

Acclimatory responses of the Daphnia pulex proteome to environmental changes. II. Chronic exposure to different temperatures (10 and 20 degrees C) mainly affects protein metabolism

BACKGROUND

Temperature affects essentially every aspect of the biology of poikilothermic animals including the energy and mass budgets, activity, growth, and reproduction. While thermal effects in ecologically important groups such as daphnids have been intensively studied at the ecosystem level and at least partly at the organismic level, much less is known about the molecular mechanisms underlying the acclimation to different temperatures. By using 2D gel electrophoresis and mass spectrometry, the present study identified the major elements of the temperature-induced subset of the proteome from differently acclimated Daphnia pulex.

RESULTS

Specific sets of proteins were found to be differentially expressed in 10 degrees C or 20 degrees C acclimated D. pulex. Most cold-repressed proteins comprised secretory enzymes which are involved in protein digestion (trypsins, chymotrypsins, astacin, carboxypeptidases). The cold-induced sets of proteins included several vitellogenin and actin isoforms (cytoplasmic and muscle-specific), and an AAA+ ATPase. Carbohydrate-modifying enzymes were constitutively expressed or down-regulated in the cold.

CONCLUSION

Specific sets of cold-repressed and cold-induced proteins in D. pulex can be related to changes in the cellular demand for amino acids or to the compensatory control of physiological processes. The increase of proteolytic enzyme concentration and the decrease of vitellogenin, actin and total protein concentration between 10 degrees C and 20 degrees C acclimated animals reflect the increased amino-acids demand and the reduced protein reserves in the animal's body. Conversely, the increase of actin concentration in cold-acclimated animals may contribute to a compensatory mechanism which ensures the relative constancy of muscular performance. The sheer number of peptidase genes (serine-peptidase-like: > 200, astacin-like: 36, carboxypeptidase-like: 30) in the D. pulex genome suggests large-scaled gene family expansions that might reflect specific adaptations to the lifestyle of a planktonic filter feeder in a highly variable aquatic environment.

Expression and purification of a cold-adapted group III trypsin in Escherichia coli

The recently classified group III trypsins include members like Atlantic cod (Gadus morhua) trypsin Y as well as seven analogues from other cold-adapted fish species. The eight group III trypsins have been characterized from their cDNAs and deduced amino acid sequences but none of the enzymes have been isolated from their native sources. This study describes the successful expression and purification of a recombinant HP-thioredoxin-trypsin Y fusion protein in the His-Patch ThioFusion Escherichia coli expression system and its purification by chromatographic methods. The recombinant form of trypsin Y was previously expressed in Pichia pastoris making it the first biochemically characterized group III trypsin. It has dual substrate specificity towards trypsin and chymotrypsin substrates and demonstrates an increasing activity at temperatures between 2 and 21 degrees C with a complete inactivation at 30 degrees C. The aim of the study was to facilitate further studies of recombinant trypsin Y by finding an expression system yielding higher amounts of the enzyme than possible in our hands in the P. pastoris system. Also, commercial production of trypsin Y will require an efficient and inexpensive expression system like the His-Patch ThioFusion E. coli expression system described here as the enzyme is produced in very low amounts in the Atlantic cod.

Olfactory specific chymotrypsin-like serine protease from the aesthetasc tegumental gland of the lobster, Homarus americanus

Numerous proteases and protease inhibitors are expressed in the lobster olfactory organ. One of these proteases, olfactory enriched transcript 03 (OET-03), is particularly interesting because its mRNA is expressed only in one cell type of the olfactory organ of the American lobster, Homarus americanus. We have obtained a full-length cDNA clone of OET-03. The predicted amino acid sequence is equally divided between a novel N-terminal domain and a conserved serine protease catalytic domain at the C-terminus. Heterologous expression in HEK293 cells allowed protease assays demonstrating that OET-03 cleaved a specific serine protease substrate, N-alpha benzoyl-L-arginine p-nitroanilide, but did not cleave a substrate of metalloproteases and cysteine proteases. OET-03 protease activity was significantly inhibited by the chymotrypsin-like protease inhibitor, tosyl-L-phenylalanine chloromethyl ketone, but not by the general protease inhibitor, phenylmethylsulfonyl fluoride. Immunoreactivity for OET-03 was detected only in the cells previously shown to contain OET-03 mRNA. The cytoplasm of these cells was filled with enlarged smooth endoplasmic reticulum (a characteristic of secretory cells) that appeared to expand into large electron-translucent areas at the ventral end of the cell. The ventral ends of these secretory cells were apposed to phalloidin-labeled triangular structures reminiscent of the beginnings of the ducts of crustacean tegumental glands. This putative gland was found only in association with the aesthetasc sensory units of the olfactory organ, hence the name, aesthetasc tegumental gland.

Atlantic cod trypsins: from basic research to practical applications

Atlantic cod trypsin I is an appropriate representative of the traditionally classified cold-adapted group I trypsins, and the recombinant form of cod trypsin Y is the only biochemically characterized member of the novel group III trypsins. Trypsin Y is adapted to lower temperatures than all other presently known trypsins. This review describes the basic characteristics of and practical uses for trypsins of Atlantic cod, as well as those of other organisms. Overexpression of the recombinant forms of cod trypsins I and Y in microorganisms is explained as well as the advantages of using site-directed mutagenesis to increase their stability toward autolysis and thermal inactivation. Trypsins appear to play a key role in the nutrition and development of marine fish. We discuss the potential use of cod trypsins as biomarkers to evaluate the nutritional status of cod larvae and describe the industrial applications of cod trypsin I and other trypsins.

Optionen des Debridements in der Therapie chronischer Wunden. Options for debridement in the therapy of chronic wounds

Debridement is defined as the removal of non-vital tissue from wounds. In chronic wounds, debridement means the elimination of necrosis as well as the clearing away of wound dressings, foreign bodies, and other non-vital substances. Sufficient debridement represents one basic prerequisite for a non-delayed wound-healing process. In addition to treating the causal factors for delayed wound healing, debridement should be the first step in an adequate phase-adapted wound-bed preparation for chronic wounds. This report aims to review the different options available in the execution of debridement in chronic wounds. The following therapeutic measures are available for the debridement of chronic wounds: surgery, maggot therapy, laser, ultrasound, hydrotherapy, wet-to-dry method, autolysis, proteolytic enzymes, osmotic or chemical debridement. There is no single correct debridement for all patients! Patients are individuals and therefore different methods of debridement may make sense. Which therapeutic option is chosen is determined by multiple factors. Moreover, depending on the wound milieu, the successive application of different methods can be useful.

Recombinant cold-adapted trypsin I from Atlantic cod-expression, purification, and identification

Atlantic cod trypsin I is a cold-adapted proteolytic enzyme exhibiting approximately 20 times higher catalytic efficiency (kcat/KM) than its mesophilic bovine counterpart for the simple amide substrate BAPNA. In general, cold-adapted proteolytic enzymes are sensitive to autolytic degradation, thermal inactivation as well as molecular aggregation, even at temperatures as low as 18-25 degrees C which may explain the problems observed with their expression, activation, and purification. Prior to the data presented here, there have been no reports in the literature on the expression of psychrophilic or cold-adapted proteolytic enzymes from fish. Nevertheless, numerous cold-adapted proteolytic microbial enzymes have been successfully expressed in bacteria and yeast. This report describes successful expression, activation, and purification of the recombinant cod trypsin I in the His-Patch ThioFusion Escherichia coli expression system. The E. coli pThioHis expression vector used in the study enabled the formation of a fusion protein between a highly soluble fraction of HP-thioredoxin contained in the vector and the N-terminal end of the precursor form of cod trypsin I. The HP-thioredoxin part of the fusion protein binds to a metal-chelating ProBond column, which facilitated its purification. The cod trypsin I part of the purified fusion protein was released by proteolytic cleavage, resulting in concomitant activation of the recombinant enzyme. The recombinant cod trypsin I was purified to homogeneity on a trypsin-specific benzamidine affinity column. The identity of the recombinant enzyme was demonstrated by electrophoresis and chromatography.

Characterization of proteinases from Antarctic krill (Euphausia superba)

Fractions of three trypsin-like proteinases, TL I, TL II, and TL III, a chymotrypsin-like proteinase, CL, two carboxypeptidase A enzymes, CPA I and CPA II and two carboxypeptidase B enzymes, CPB I and CPB II, from Antarctic krill (Euphausia superba) have been characterized with respect to purity by the means of capillary electrophoresis, CE, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The masses of the trypsin-like and chymotrypsin-like proteinases were determined to be 25,020, 25,070, 25,060, and 26,260Da for TL I, TL II, TL III, and CL, respectively. The masses of the CPA enzymes are likely 23,170 and 23,260Da, whereas the CPB enzyme masses likely are 33,730 and 33,900Da. The degradation efficiency and cleavage pattern of the trypsin-like proteinases were studied with native myoglobin as a model substrate using CE, MALDI-TOF-MS, and nanoelectrospray mass spectrometry (nESI-MS). The degradation efficiency of the trypsin-like proteinases was found to be approximately 12 and 60 times higher compared to bovine trypsin at 37 degrees C and 1-3 degrees C, respectively. All three fractions of trypsin-like proteinases showed a carboxypeptidase activity in combination with their trypsin activity.

Cold-adapted and mesophilic brachyurins

Two different types of brachyurins, termed I and II, have been described in the literature. Within type I there are two subtypes, Ia and Ib. The prototype for the type I brachyurins is Fiddler crab collagenase I. Its cold-adapted analogue from Antarctic krill, termed euphaulysin, shares many of its characteristics. Both enzymes are distinguished by their broad substrate specificity as well as the ability to cleave collagen. The precursor form of euphaulysin has been expressed in Pichia pastoris and processed to its fully active form using cod trypsin. A molecular model of euphaulysin, based on the known crystal structure of crab collagenase I, indicates that the core structure of these enzymes is almost identical. As a cold-adapted enzyme, euphaulysin has a higher catalytic efficiency than crab collagenase I. It is also more sensitive to thermal inactivation and autolysis. Furthermore, euphaulysin has an increased length of several surface loops compared to crab collagenase I. Extended surface loops have been suggested to play a role in the cold activity of some bacterial enzymes. Sensitivity to autolysis is an important factor which contributes to the thermal instability of euphaulysin. Substitution of a highly exposed residue in the 'autolysis loop' of euphaulysin resulted in an increased stability of the enzyme towards thermal inactivation without altering its catalytic efficiency.

Low-temperature extremophiles and their applications

Psychrophilic (cold-adapted) organisms and their products have potential applications in a broad range of industrial, agricultural and medical processes. In order for growth to occur in low-temperature environments, all cellular components must adapt to the cold. This fact, in combination with the diversity of Archaea, Bacteria and Eucarya isolated from cold environments, highlights the breadth and type of biological products and processes that might be exploited for biotechnology. Relative to this undisputed potential, psychrophiles and their products are under-utilised in biotechnology; however, recent advances, particularly with cold-active enzymes, herald rapid growth for this burgeoning field.