Improvement of shark type I collagen with microbial transglutaminase in urea

In the presence of urea, type I collagen could form a gel with crosslinks with microbial transglutaminase (MTGase). Collagen self-assembly was accelerated with the addition of MTGase. The proportion of reconstructed collagen fibrils was raised with the addition of MTGase. MTGase-treated collagen gel remained gelled at high temperatures at which collagen denatured. By treatment with MTGase, collagen could form the gel under impossible condition to collagen self-assembly, and that denaturation temperature was raised.     

Improvement of Shark Type I Collagen with Microbial Transglutaminase in Urea

In the presence of urea, type I collagen could form a gel with crosslinks with microbial transglutaminase (MTGase). Collagen self-assembly was accelerated with the addition of MTGase. The proportion of reconstructed collagen fibrils was raised with the addition of MTGase. MTGase-treated collagen gel remained gelled at high temperatures at which collagen denatured. By treatment with MTGase, collagen could form the gel under impossible condition to collagen self-assembly, and that denaturation temperature was raised.     

The optical interconversion of the P-450 and P-420 forms of neuronal nitric oxide synthase: effects of sodium cholate, mercury chloride and urea

We investigated whether or not neuronal nitric oxide synthase (nNOS) (EC 1.14.13.39) was converted to the P-420 form on exposure to sodium cholate, mercury chloride or urea, and the reconversion of the P-420 to the P-450 form. Sodium cholate and mercury chloride induced the conversion of nNOS from the P-450 to the P-420 form in concentration- and incubation time-dependent manners, and the nNOS activity decreased. In the presence of glycerol, L-arginine and/or tetrahydrobiopterin, the sodium cholate-treated P-420 form could be reconverted to the P-450 form under constant experimental conditions, and the nNOS activity could also be restored. The mercury chloride-treated P-420 form of nNOS could be reconverted to the P-450 form on incubation with reduced glutathione (GSH) or L-cysteine, and the nNOS activity was recovered. However, no reconversion of the mercury chloride-treated P-420 form to the P-450 form was observed in the presence of glycerol, L-arginine, or tetrahydrobiopterin. Urea (4.0 M) dissociated nNOS into its subunits, but nNOS remained in the P-450 form. The nNOS monomer was more susceptible to sodium cholate. After removing the urea by dialysis, and supplementation of the nNOS solution with glycerol, L-arginine or BH(4), the P-420 was reconverted to the P-450 form, and the reassociation of nNOS monomers was also observed. These results suggested that nNOS was more stable as to exposure to sodium cholate, mercury chloride or urea in comparison to microsomal cytochrome P-450, which may be due to the different heme environment and protein structure.     

Resistance to deactivation of enzyme-collagen membranes

Amongst the attractive properties of immobilized enzymes, an enhanced stability is very often underlined. In our case, the covalent attachment of numerous enzymes from different classes to water-insoluble collagen films allowed us to study their resistance to inactivation or denaturation after coupling. The influence of heat, denaturing reagents like concentrated urea or guanidinium chloride, the incubation in the presence of glutaraldehyde, have been tested on aspartate amino-transferase either in soluble form or bound on collagen films. The fact that diffusional effects can lead to an apparent enhancement of stability after immobilization has been taken into account and their influence studied for both thermal and storage stability : diffusional limitations are partly responsible for the enhanced stability of the bound enzyme but the binding to the collagen membrane itself increases its storage stability. The resistance of proteolytic enzymes to autolysis has also been checked.     

Procollagen synthesis and processing in periodontal ligament in vivo and in vitro. A comparative study using slab-gel fluorography.

A combination of dodecylsulphate/polyacrylamide gel electrophoresis and fluorography has been used to quantify the synthesis of type I and type III collagens by periodontal ligament in situ and periodontal-ligament fibroblasts in vitro. The separation of 14C-labelled collagen alpha chains was achieved by introducing an interrupted reduction step, and the total radioactivity in the alpha-chain bands related to the fluorographic response by a series of standard curves. From these curves an accurate assessment of the relative amounts of type I and III collagen synthesized could be made. The same system also allowed the synthesis and processing of the respective procollagens to be analyzed. For the study in vivo, 200-g male rats were injected with 2 mCi [14C]glycine and killed 0.5-6 h later. Periodontal ligament was dissected from the mandibular molars and the newly-synthesized collagens extracted with 0.45 M sodium chloride. In the study in vitro, confluent monkey periodontal-ligament fibroblasts were cultured in the presence of [14C]proline and [14C]glycine. Analysis of labelled collagens showed a rapid conversion of type I procollagen to collagen but type III collagen was recovered as a procollagen intermediate both in vitro and in vivo. Analysis of duplicate samples after pepsin digestion showed type III collagen synthesis to comprise 15% of the total collagen synthesized in vivo and 20% in early subcultures in vitro. However, the proportion of type III synthesized by the fibroblasts decreased on subculturing. The data demonstrate that fibroblasts in vitro retain the basic characteristics of collagen synthesis and procollagen processing found in vivo, but the overall phenotypic expression of the cells is not stable in culture.     

Propidium iodide as a probe for the study of chromatin thermal denaturationin situ

Summary The possibility of using propidium iodide, a phenanthridinic fluorochrome specific for double-stranded nucleic acids, for the study of chromatin thermal denaturationin situ has been examined. Smears of lymphocytes and hepatocyte nuclei from 15-day-old rats were fixed in acetic acid-ethanol (13 v/v), treated with RNAse and submitted to different protein extraction procedures, namely, incubation with pepsin, trypsin and sodium chloride.Denaturation experiments were performed in Sörensen buffer at pH 7.4 containing 10% formamide at temperatures between 27 and 95°C. The samples were stained with propidium iodide and mounted in buffer or glycerol. Measurements were performed with a microfluorometer at a wavelength of 546 nm.The results indicate a higher thermostability of lymphocytes as compared to hepatocytes. The denaturation pattern suggests a certain organization complexity of chromatin, better emphasized by the derivative curves which show the presence of at least three fractions with different melting points. After protein extraction, the denaturation curves exhibit a somewhat simplified pattern, with the disappearance of the most stable peak in the derivative curves. The samples mounted in glycerine exhibit a better stability of staining with time, and an increased quantum efficiency of the fluorochrome with regard to those mounted in buffer.These data confirm the importance of protein-DNA interactions in the organization of chromatin and point to some differences, depending on the cell type and on functional activity.     

Influence of collagen denaturation on the chemorheological properties of skin,assessed by differential scanning calorimetry and hydrothermal isometric tension measurement

The curves obtained for skin samples of different ages and species by hydrothermal isometric tension (‘HIT’) measurement are compared to those obtained by differential scanning calorimetry (DSC) under the same thermal conditions (for a rise in temperature at a rate of 1.0°C/min). Collagen denaturation, observed by DSC, directly affects the kinetics of the tension variations in the first part of the ‘HIT’ curves, including the early peak due to the presence and destruction of the heat-labile cross-links in the collagen network. The presence of cross-links is in term shown to delay collagen denaturation to an extent which depends in part on their heat-stability. The final part of the ‘HIT’ curves reflecting the effects of heat in the stable polymeric collagen network is no longer affected by collagen denaturation. Thus, both ‘HIT’ and DSC are useful methods to evaluate collagen reticulation in connective tissues.     

Isolation and characterization of collagen from the cartilage of Amur sturgeon (Acipenser schrenckii)

The collagen in Amur sturgeon cartilage was isolated using sodium chloride (salt-solubilized collagen, SSC, 2.18%), followed by acetic acid (acid-solubilized collagen, ASC, 27.04%) and then pepsin (pepsin-solubilized collagen, PSC, 55.92%). These collagens appeared to be dense sheet-like film linked by random-coiled filaments under SEM. The denaturation and melting temperatures of PSC (35.71 and 123.90 °C) were significantly higher than SSC (32.64 and 114.51 °C) and ASC (32.98 and 120.72 °C) assessed by circular dichroism and differential scanning calorimetry, which could be attributed to its high imino acid content (22.57%) and degree of hydroxylation (47.29%). Electrophoresis pattern showed that the SSC and ASC were type I collagen, while PSC was predominantly type II collagen along with other minor types. Infrared spectra confirmed their triple helical structure, and indicated more hydrogen bonding in ASC and more intermolecular crosslinks in PSC. These results provide some basis for their large-scale production and further application as alternatives to mammalian collagen.     

Separation of the alpha chains of type I and III collagens by SDS-polyacrylamide gel electrophoresis.

A method for the separation of type III collagen from type I collagen by SDS-polyacrylamide gel electrophoresis has been developed. This is based on the observation that the presence of 3-4 M urea decreases the mobility of the alpha 1 [III] chain to a greater extent than those of the alpha 1[I] and alpha 2 chains, although the alpha 1[I] and alpha 1[III] chains move at the same rate in the absence of urea. An attempt to separate the alpha 1[II] chain of type II collagen from the alpha 1[I] chain was unsuccessful under the experimental conditions employed.     

Collagen denaturation in spread monolayers at the air-water interface: Experiments and a possible model of the process

Spread monolayers of the fibril protein collagen were studied at the air-water interface in the presence of denaturants, urea and thiourea. The most prominent feature of spread collagen monolayers at the air-water interface is the ability to form supramolecular structures (fibrils), which themselves can form monolayers with collapse points of their own. The surface pressure isotherms of collagen monolayers have two “quasi-linear” centers, which are separated by a plateau and correspond to liquid-expanded and liquid-condensed states; this unique capability makes collagen different from other proteins. When in monolayer, collagen acquires the same level of structural organization as in the bulk. In the presence of denaturants, subphase characteristics of collagen monolayers change rapidly and irreversibly. Thiourea exerts more pronounced denaturing action on collagen monolayers than urea; this effect increases with exposure time and denaturant concentration. A hypothetical mechanism of thiourea-induced denaturation of fibril proteins is proposed according to which interactions between hydrophobic C=S groups of thiourea and nonpolar surface groups of the protein lead to reorientation of carbonyl groups to formation of intrinsic hydrogen bonds with NH₂-groups of thiourea eventually resulting in the rupture of intrinsic hydrogen bonds and denaturation of the protein.     

Type I collagen prevents amyloid aggregation of hen egg white lysozyme

Both collagen and amyloidogenic proteins have an inherent ability to undergo a self-assembly process leading to formation of supramolecular structures. Though our understanding of collagen–amyloid link is very poor, a few experimental evidences have indicated the protective nature of collagen against amyloid fibril formation. To further our understanding of collagen–amyloid relationship, we have explored the role of type I collagen on amyloid-aggregation of lysozyme. Thioflavin-T assay data indicated strong inhibition of both spontaneous and seeded aggregation of lysozyme by collagen. Both chemical and thermal denaturation experiments have showed increased lysozyme stability in the presence of collagen. However, the presence of collagen did not alter lysozyme activity. These findings confirm that type I collagen is capable of blocking or interfering with the amyloid aggregation of lysozyme, and the results may have significant implications for the design of collagen based therapeutics against aggregation of disease linked amyloidogenic proteins.     

Biosynthesis and deposition of a noncovalent laminin-heparan sulfate proteoglycan complex and other basal lamina components by a human malignant cell line

The basal lamina components laminin, heparan sulfate proteoglycan (HSPG), and type IV collagen were synthesized and codeposited in the extracellular matrix (ECM) by a cultured human cell line from gestational choriocarcinoma (JAR). Laminin and HSPG formed a noncovalent complex detected by the coimmunoprecipitation of HSPG with laminin from cell lysates and culture media. The complex was stable in the cell lysis buffer that contained detergents (1% Triton X-100, 0.5% deoxycholate, and 0.1% sodium dodecyl sulfate) and sodium chloride (from 0.15 to 1.0 M), but was dissociated by adding 8 M urea to the detergent lysates. Even though JAR cells produced roughly equal amounts of HSPG and chondroitin sulfate proteoglycan, only HSPG complexed with laminin, suggesting a specific interaction between these basal lamina components. The laminin-HSPG complex was deposited and retained in the ECM. This was shown biochemically by isolating an enriched fraction of ECM from JAR cells cultured on native type I collagen gels. At steady state, more than half (52%) of the laminin-HSPG in the culture was recovered in the ECM fraction, in contrast to 16% of the total laminin and 29% of the total type IV collagen, which were secreted to a greater extent than laminin-HSPG into the culture medium. The retention of the laminin-HSPG complex in the ECM suggests that it may participate in the assembly of the basal lamina-like extracellular matrix deposited by JAR cultures. Omission of ascorbate from the culture medium abolished the ECM deposition of type IV collagen but had little effect on the deposition of laminin or laminin-HSPG. This demonstrates that the stable deposition of laminin-HSPG and laminin in the collagen-based choriocarcinoma cultures is not dependent on an assembled network of type IV collagen.     

Comparison of extracellular matrix-degrading activities between 64-kDa and 90-kDa gelatinases purified in inhibitor-free forms from human schwannoma cells.

Two kinds of gelatinases (or type IV collagenases), 90-kDa and 64-kDa gelatinases, were purified in a tissue inhibitor of metalloproteinases (TIMP)- or TIMP-2-free form from the serum-free conditioned medium of human schwannoma YST-3 cells, and their activities on extracellular matrix proteins were compared. Sequential chromatographies on a gelatin-Sepharose column, an LCA-agarose column, and a gel filtration column in the presence of 5 M urea yielded 600 micrograms of the 64-kDa enzyme and 45 micrograms of the 90-kDa enzyme from 2.8 liters of the conditioned medium. The purified enzymes showed high gelatinolytic activities without activation by p-aminophenyl mercuric acetate (APMA), indicating that 5 M urea used in the final chromatography not only dissociated the inhibitors from the progelatinases but also activated the proenzymes. The inhibitor-free gelatinases showed a much higher activity than the APMA-activated inhibitor-bound enzymes. The specific activity of the 90-kDa enzyme was nearly 25 times higher than that of the 64-kDa enzyme. The 90-kDa gelatinase hydrolyzed type I collagen as well as native and pepsin-treated type IV collagens at 30 degrees C, while at 37 degrees C it potently hydrolyzed types I, III, and IV collagens but not fibronectin or laminin. The 64-kDa gelatinase showed a similar substrate specificity to that of the 90-kDa enzyme, except that it did not hydrolyze type I collagen and native type IV collagen at 30 degrees C.     

Photo-cross-linking of type I collagen gels in the presence of smooth muscle cells: mechanical properties,cell viability,and function

The effectiveness of photomediated cross-linking of type I collagen gels in the presence of rat aortic smooth muscle cells (RASMC) as a method to enhance gel mechanical properties while retaining native collagen triple helical structure and maintaining high cell viability was investigated. Collagen was chemically modified to incorporate an acrylate moiety. Collagen methacrylamide was cast into gels in the presence of a photoinitiator along with RASMC. The gels were cross-linked using visible light irradiation. Neither acrylate modification nor the cross-linking reaction altered collagen triple helical content. The cross-linking reaction, however, moved the denaturation temperature beyond the physiologic range. A twelve-fold increase in shear modulus was observed after cross-linking. Cell viability in the range of 70% (n = 4, p > 0.05) was observed in the photo-cross-linked gels. Moreover the cells were able to contract the cross-linked gel in a manner commensurate with that observed for natural type I collagen. Methacrylate-mediated photo-cross-linking is a facile route to improve mechanical properties of collagen gels in the presence of cells while maintaining high cell viability. This enhances the potential for type I collagen gels to be used as scaffolds for tissue engineering.     

Unfolding-refolding behaviour of chicken egg white ovomucoid and its correlation with the three domain structure of the protein

The urea and heat-induced unfolding-refolding behaviours of chicken egg white ovomucoid and its four fragments representing domains I, II + III, I + II and III were systematically investigated in 0.06 M sodium phosphate buffer (pH 7.0) by difference spectral measurements. The effect of temperature on ovomucoid and its fragments was also studied in 0.05 M sodium acetate buffer (pH 5.0) and in presence of 2 M urea at pH 7.0. Intrinsic viscosity data showed that ovomucoid and its different fragments did not lose any significant amount of their structure under mild acidic conditions (pH 4.6). Difference spectral results showed extensive disruption of the native structure by urea or temperature. Isothermal transitions showed single-step for domain I, domain I + II and domain III, and two-step having one stable intermediate, for ovomucoid and its fragment representing domain II + III. However, the presence of intermediate was not detected when the transitions were studied with temperature at pH 7.0. Strikingly, the single-step thermal transitions of ovomucoid and its fragment representing domain II + III, became two-step when measured either at pH 5.0 or in presence of 2 M urea at pH 7.0. Analysis of the equilibrium data on urea and heat denaturation showed that the second transition observed with ovomucoid or domain II + III represent the unfolding of domain III. The kinetic results of ovomucoid and its fragments indicate that the protein unfolds with three kinetic phases. A comparison of three rate constants for the unfolding of intact ovomucoid with that of its various fragments revealed that domain I, II and III of the protein correspond to the three kinetic phases having rate constants 0.456, 0.120 and 0.054 min-1, respectively. These data have led us to conclude: (i) the unusual stability of ovomucoid towards various denaturants, including temperature, is due to its domain III, (ii) initiation of the folding of the ovomucoid molecule starts from its NH2-terminal region which probably provides the nucleation site for the formation of the subsequent structure and (iii) domains I and II have greater mutual recognition between them as compared to the recognition either of them have with domain III.     

The thermal behavior of collagen in solution: effect of glycerol and 2-propanol

The thermal stability of different solutions of collagen (Col), collagen mixed with glycerol (Col-G) and collagen mixed with 2-propanol (Col-P) was studied by differential scanning calorimetry (DSC), viscosity and fluorescence. The DSC and viscosity methods showed that glycerol increased the denaturation temperature of collagen about 2°C, while 2-propanol decreased it about 2°C. The values of intrinsic viscosity ([η]) for Col, Col-G and Col-P were 21.67, 20.20 and 24.71 dl/g, respectively. Huggins coefficient (k(H)) increased in the presence of glycerol and decreased in the presence of 2-propanol. It was suggested that glycerol promoted the dissolution of collagen molecular aggregates while 2-propanol enhanced the aggregation. Fluorescence spectra were investigated within the temperature ranging from 15 to 45°C. By comparing the sign of peaks in the two-dimensional (2D) fluorescence correlation maps, the orders of peak response were ～360, ～410>297 nm for Col and Col-G, and 297>～360, ～410 nm for Col-P, respectively. These indicated that the respondences of tyrosine residues, excimer-like species and bityrosine on the perturbation of temperature were different in the presence of glycerol and 2-propanol.     

Studies on alpha-amylase from a thermophilic bacterium. II. Thermal stability of the thermophilic alpha-amylase.

The effect of pH, mental ions, and denaturing reagents on the thermal stability of thermophilic alpha-amylase [EC 3.2.1.1] were examined. The enzyme was most stable at around pH 9.2, which is coincident with the isoelectric point of the enzyme. The stability of the enzyme was increased by the addition of calcium, strontium, and sodium ions. The addition of calcium ions markedly stabilized the enzyme. The protective effects of calcium and sodium ions were additive. At room temperature, no detectable destruction of the helical structure of the enzyme was observed after incubation for 1 hr in the presence of 1% sodium dodecylsulfate, 8 M urea or 6 M guanidine-HC1. The addition of 8 M urea or 6 M guanidine-HC1 lowered the thermal denaturation temperature of the enzyme. The enzyme contained one atom of tightly bound intrinsic calcium per molecule which could not be removed by electrodialysis unless the enzyme was denatured. The rate constants of inactivation and denaturation reactions in the absence and presence of calcium ions were measured and thermodynamic parameters were determined. The presence of calcium ions caused a remarkable decrease in the activation entropy.     

Structural transition during thermal denaturation of collagen in the solution and film states

Temperature dependent vibrational circular dichroism (VCD) spectra of type I collagen, in solution and film states, have been measured. These spectra obtained for solution sample suggest that the thermal denaturation of collagen results in transition from poly-L-proline II (PPII) to unordered structure. The PPII structure of collagen is identified by the presence of negative VCD couplet in the amide I region, while the formation of unordered structure is indicated by the disappearance of VCD in the amide I region. The temperature dependent spectra obtained for the supported collagen film indicated a biphasic transition, which is believed to be the first vibrational spectroscopic report to support a biphasic transition during thermal denaturation of collagen film. The temperature dependent spectra of collagen films suggest that the thermal stability of collagen structure depends on its state and decreases in the order: supported film > free standing film > solution state. These observations are believed to be significant in the VCD spectroscopic analysis of secondary structures of proteins and peptides.     

Thermal stabilty of glucokinase (GK) as influenced by the substrate glucose, an allosteric glucokinase activator drug (GKA) and the osmolytes glycerol and urea

We investigated how glycerol, urea, glucose and a GKA influence kinetics and stability of wild-type and mutant GK. Glycerol and glucose stabilized GK additively. Glycerol barely affected the TF spectra of all GKs but decreased k(cat), glucose S(0.5) and K(D) values and ATP K(M) while leaving cooperativity unchanged. Glycerol sensitized all GKs to GKA as shown by TF. Glucose increased TF of GKs without influence of glycerol on the effect. Glycerol and GKA affected kinetics and binding additively. The activation energies for thermal denaturation of GK were a function of glucose with K(D)s of 3 and 1mM without and with glycerol, respectively. High urea denatured wild type GK reversibly at 20 and 60°C and urea treatment of irreversibly heat denatured GK allowed refolding as demonstrated by TF including glucose response. We concluded: Glycerol stabilizes GK indirectly without changing the folding structure of the apoenzyme, by restructuring the surface water of the protein, whereas glucose stabilizes GK directly by binding to its substrate site and inducing a compact conformation. Glucose or glycerol (alone or combined) is unable to prevent irreversible heat denaturation above 40°C. However, urea denatures GK reversibly even at 60°C by binding to the protein backbone and directly interacting with hydrophobic side chains. It prevents irreversible aggregation allowing complete refolding when urea is removed. This study establishes the foundation for exploring numerous instability mutants among the more than 600 variant GKs causing diabetes in animals and humans.     

Isolation of collagen from the skins of Ehlers-Danlos syndrome-affected dogs by acetic acid extraction and pepsin digestion

Collagen was isolated by acetic acid extraction in the presence of protease inhibitors and also by pepsin digestion from the skins of dogs affected with the Ehlers-Danlos syndrome and the skins on non-affected dogs. The collagen preparations isolated by acetic acid extraction from the Ehlers-Danlos syndrome-affected dog skin contained a greater proportion of alpha-chains than the collagen preparations from the normal dog skin. When the collagen from the Ehlers-Danlos syndrome-affected dog skin was reduced with NaBH4 before heat denaturation, and electrophoresis, there was a greater proportion of beta-chains present. The collagen isolated from the normal dog skin was not affected by the NaBH4 reduction. Collagen preparations isolated by pepsin digestion from both the Ehlers-Danlos syndrome-affected dog skin and the non-affected dog skin contained the same quantity of alpha- and beta-chains. In addition, collagen from both affected and non-affected dog skins isolated by pepsin digestion contained 10-11% type III collagen as determined by the interrupted sodium dodecyl sulfate polyacrylamide gel electrophoresis method. Pepsin digestion of the collagens isolated by acetic acid extraction in the presence of protease inhibitors from the skins of affected and non-affected dogs eliminated the differences between the alpha:beta ratios of the affected and non-affected collagen preparations.