Structural Basis for Activity Regulation and Substrate Preference of Clostridial Collagenases G,H, and T

Clostridial collagenases are among the most efficient enzymes to degrade by far the most predominant protein in the biosphere. Here we present crystal structures of the peptidases of three clostridial collagenase isoforms (ColG, ColH, and ColT). The comparison of unliganded and liganded structures reveals a quaternary subdomain dynamics. In the unliganded ColH structure, this globular dynamics is modulated by an aspartate switch motion that binds to the catalytic zinc. We further identified a calcium binding site in proximity to the catalytic zinc. Both ions are required for full activity, explaining why calcium critically affects the enzymatic activity of clostridial collagenases. Our studies further reveal that loops close to the active site thus serve as characteristic substrate selectivity filter. These elements explain the distinct peptidolytic and collagenolytic activities of these enzymes and provide a rational framework to engineer collagenases with customized substrate specificity as well as for inhibitor design.     

High-level expression of his-tagged clostridial collagenase in Clostridium perfringens

Clostridium histolyticum collagenase is used to isolate cells from various organs and tissues for tissue engineering, and also to treat destructive fibrosis; thus, the demand for high-grade enzyme preparations is increasing. In this study, we constructed a plasmid encoding C. histolyticum type II collagenase (ColH) with a C-terminal hexahistidine tag (ColH-his) to facilitate the purification of the enzyme through immobilized metal affinity chromatography (IMAC). When ColH-his was expressed in a protease-deficient mutant of Clostridium perfringens, it was produced in the culture supernatant more efficiently than the untagged ColH. ColH-his exhibited the same hydrolytic activity as ColH against 4-phenylazobenzyloxy-carbonyl-Pro-Leu-Gly-Pro-D: -Arg (Pz peptide), a synthetic collagenase substrate. From 100 ml of the culture supernatant, approximately 1 mg of ColH-his was purified by ammonium sulfate precipitation, IMAC, and high-performance liquid chromatography on a MonoQ column. When IMAC was performed on chelating Sepharose charged with Zn(2+) instead of Ni(2+), a potential carcinogenic metal, the specific activities against Pz peptide and type I collagen decreased slightly. However, they were comparable to those reported for other recombinant ColHs and a commercial C. histolyticum collagenase preparation, suggesting that this expression system is useful for large-scale preparation of high-grade clostridial collagenases.     

A universal strategy for high-yield production of soluble and functional clostridial collagenases in <Emphasis Type="Italic">E. coli</Emphasis>

Clostridial collagenases are foe and friend: on the one hand, these enzymes enable host infiltration and colonization by pathogenic clostridia, and on the other hand, they are valuable biotechnological tools due to their capacity to degrade various types of collagen and gelatine. However, the demand for high-grade preparations exceeds supply due to their pathogenic origin and the intricate purification of homogeneous isoforms. We present the establishment of an Escherichia coli expression system for a variety of constructs of collagenase G (ColG) and H (ColH) from Clostridium histolyticum and collagenase T (ColT) from Clostridium tetani, mimicking the isoforms in vivo. Based on a setup of five different expression strains and two expression vectors, 12 different constructs were expressed, and a flexible purification platform was established, consisting of various orthogonal chromatography steps adaptable to the individual needs of the respective variant. This fast, cost-effective, and easy-to-establish platform enabled us to obtain at least 10 mg of highly pure mono-isoformic protein per liter of culture, ideally suited for numerous sophisticated downstream applications. This production and purification platform paves the way for systematic screenings of recombinant collagenases to enlighten the biochemical function and to identify key residues and motifs in collagenolysis.     

Limited proteolysis of type I collagen at hyperreactive sites by class I and II Clostridium histolyticum collagenases: complementary digestion patterns

The initial proteolytic events in the hydrolysis of rat tendon type I collagen by the class I and II collagenases from Clostridium histolyticum have been investigated at 15 degrees C. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis has been used to detect the initial cleavage fragments of both the alpha 1(I) and alpha 2 chains, which migrate at different rates in the buffer system employed. Experiments with the class I collagenases indicate that the first cleavage occurs across all three chains of the triple helix close to the C-terminus to produce fragments whose alpha chains have molecular weights of approximately 88,000. The second cleavage occurs near the N-terminus to reduce the molecular weight of the alpha chains to 80,000. Initial proteolysis by the class II collagenases occurs across all three chains at a site in the interior of the collagen triple helix to give N- and C-terminal fragments with alpha-chain molecular weights of 35,000 and 62,000, respectively. The C-terminal fragment is subsequently cleaved to give fragments with alpha-chain molecular weights of 59,000. These results indicate that type I collagen is degraded at several hyperreactive sites by these enzymes. Thus, initial proteolysis by these bacterial collagenases occurs at specific sites, much like the mammalian collagenases. These results with the individual clostridial collagenases provide an explanation for earlier data which indicated that collagen is degraded sequentially from the ends by a crude clostridial collagenase preparation.     

Nereis cuticle collagen. Proteolysis by marine vibrial and clostridial collagenases

Proteolysis of Nereis cuticle collagen by two bacterial collagenases was investigated using viscosimetry, enzyme kinetics, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and ion exchange chromatography of collagenolytic peptides. Collagenase of the marine Vibrio B-30 completely degrades native cuticle collagen at 7 degress C with a turnover number 50 times greater than that of the clostridial collagenase. Although turnover numbers for the two enzymes are comparable when using denatured cuticle collagen as substrate, the vibrial collagenase appears to cleave twice as many peptide bonds per mg of cuticle collagen as does the clostridial enzyme. Sodium dodecyl sulfate gel electrophoresis of collagenase-digested native cuticle collagen reflects the resistance of the collagen to clostridial collagenase; however, the vibrial enzyme completely degrades the cuticle collagen with the formation of one transient intermediate (Mr 400,000). Peptide analysis of fully digested denatured cuticle collagen reveals that the two enzymes have a number of qualitative and quantitative similarities. Despite these, however, only the vibrial collagenase seems capable of extensively degrading native cuticle collagen.     

Purification and properties of individual collagenases fromStreptomyces sp. strain 3B

Streptomyces strain 3B constitutively secreted collagenolytic enzymes during the post-exponential growth phase. Purification is described here leading to two collagenases (I and II) with specific activity of 3350 and 3600 U/mg, respectively, the highest activity obtained as yet for any streptomycete collagenase. Analysis of the purified enzymes by the method of zymography revealed that both I and II were homogeneous, with molar mass 116 and 97 kDa, respectively. Both collagenases were identical in their pH (7.5) and temperature optimum (37 degrees C). The inhibition profile of the enzymes by EDTA and 1,10-phenanthroline confirmed these enzymes to be metalloproteinases. By testing the activity with insoluble collagen, acid soluble collagen, gelatin, casein, elastin and Pz-PLGPR it was established that I and II are very specific for insoluble collagen and gelatin, showing a high activity toward acid soluble collagen and Pz-PLGPR. However, collagenases I and II failed to hydrolyze casein and elastin; they belong to true collagenases and resemble the clostridial enzymes.     

Enhancement of the structural stability of full-length clostridial collagenase by calcium ions

The clostridial collagenases G and H are multidomain proteins. For collagen digestion, the domain arrangement is likely to play an important role in collagen binding and hydrolysis. In this study, the full-length collagenase H protein from Clostridium histolyticum was expressed in Escherichia coli and purified. The N-terminal amino acid of the purified protein was Ala31. The expressed protein showed enzymatic activity against azocoll as a substrate. To investigate the role of Ca(2+) in providing structural stability to the full-length collagenase H, biophysical measurements were conducted using the recombinant protein. Size exclusion chromatography revealed that the Ca(2+) chelation by EGTA induced interdomain conformational changes. Dynamic light scattering measurements showed an increase in the percent polydispersity as the Ca(2+) was chelated, suggesting an increase in protein flexibility. In addition to these conformational changes, differential scanning fluorimetry measurements revealed that the thermostability was decreased by Ca(2+) chelation, in comparison with the thermal melting point (T(m)). The melting point changed from 54 to 49°C by the Ca(2+) chelation, and it was restored to 54°C by the addition of excess Ca(2+). These results indicated that the interdomain flexibility and the domain arrangement of full-length collagenase H are reversibly regulated by Ca(2+).     

New Achromobacter collagenase and its immunological relationship with a vertebrate collagenase

Evidence is presented that Achromobacter iophagus produces two distinct collagenases. Achromobacter collagenases A and B were separated by high-performance liquid chromatography from partially purified enzyme. The main collagenase, A (EC 3.4.24.8), which has been already described, was eluted in the region of molecular mass 110-90 kDa. A minor collagenase B eluted in the region of 320 kDa, although in SDS-gel electrophoresis the apparent molecular masses of its main active forms were estimated as 55 and 110 kDa. The specificities of collagenases A and B are different. Collagenase A splits in its synthetic substrate Pz-Pro-Leu-Gly-Pro-DArg the bond Leu-Gly, collagenase B does not split this substrate. Both collagenases split bonds Gln-Gly and Leu-Gly in synthetic peptides DNP-Pro-Gln-Gly-Ile-Ala-Gly-Gln-DArg-OH and DNP-Pro-Leu-Gly-Ile-Ala-Gly-DArg-NH2, respectively. Collagenase B is twice as active as A on the native collagen type I. Both enzymes are inhibited by EDTA. The antibodies raised against the human tooth collagenase specifically inhibited the collagenase B, but did not influence the activity of collagenase A. These results indicate, to our knowledge for the first time, an immunological relationship between a bacterial and a vertebrate collagenase.     

A convenient fluorescent assay for vertebrate collagenases

A versatile, convenient assay for vertebrate collagenases has been developed using the fluorescent peptide substrate dansyl-Pro-Gln-Gly-Ile-Ala-Gly-D-Arg. This sequence resembles that of collagen at the site of cleavage but includes modifications designed to eliminate nonspecific hydrolysis by contaminating peptidases. Both human skin fibroblast and bovine corneal cell collagenases cleave the substrate specifically at the Gly-Ile bond. Plasmin, thrombin, trypsin, alpha-chymotrypsin, carboxypeptidase B, and bacterial collagenase do not cleave the substrate. Elastase and angiotensin converting enzyme display 20- and 400-fold less activity than the vertebrate collagenases, respectively, and cleave the peptide at different positions. The assay is performed by incubating a 5- to 25-microliters aliquot of trypsin-activated sample with an equal volume of 2 mM substrate overnight at 33 degrees C and pH 7.5. Thin-layer chromatography then separates the fluorescent product from the substrate in less than 20 min and allows the detection of subnanogram levels of collagenase. The assay is applicable to the screening of large numbers of samples under different conditions of pH and ionic strength and is readily adaptable for use in a variety of collagenase-dependent systems, such as assays for collagenase activating and/or inducing factors.     

Crystal structure of Grimontia hollisae collagenase provides insights into its novel substrate specificity toward collagen

Collagenase from the gram-negative bacterium Grimontia hollisae strain 1706B (Ghcol) degrades collagen more efficiently even than clostridial collagenase, the most widely used industrial collagenase. However, the structural determinants facilitating this efficiency are unclear. Here, we report the crystal structures of ligand-free and Gly-Pro-hydroxyproline (Hyp)-complexed Ghcol at 2.2 and 2.4 Å resolution, respectively. These structures revealed that the activator and peptidase domains in Ghcol form a saddle-shaped structure with one zinc ion and four calcium ions. In addition, the activator domain comprises two homologous subdomains, whereas zinc-bound water was observed in the ligand-free Ghcol. In the ligand-complexed Ghcol, we found two Gly-Pro-Hyp molecules, each bind at the active site and at two surfaces on the duplicate subdomains of the activator domain facing the active site, and the nucleophilic water is replaced by the carboxyl oxygen of Hyp at the P1 position. Furthermore, all Gly-Pro-Hyp molecules bound to Ghcol have almost the same conformation as Pro-Pro-Gly motif in model collagen (Pro-Pro-Gly)₁₀, suggesting these three sites contribute to the unwinding of the collagen triple helix. A comparison of activities revealed that Ghcol exhibits broader substrate specificity than clostridial collagenase at the P2 and P2′ positions, which may be attributed to the larger space available for substrate binding at the S2 and S2′ sites in Ghcol. Analysis of variants of three active-site Tyr residues revealed that mutation of Tyr564 affected catalysis, whereas mutation of Tyr476 or Tyr555 affected substrate recognition. These results provide insights into the substrate specificity and mechanism of G. hollisae collagenase.     

Purification of human collagenases with a hydroxamic acid affinity column

Human collagenase has been isolated from skin fibroblasts and rheumatoid synovium by using an affinity matrix, prepared by coupling Pro-Leu-Gly-NHOH to agarose. Following the methodology described herein, the skin enzyme was isolated in two steps in 76% yield and the synovial enzyme was purified in three steps in 71% yield. Importantly, each enzyme hydrolyzed collagen into 3/4-1/4 cleavage fragments, indicating that a true collagenase had been isolated. The column was specific for the human enzyme since the collagenase from Clostridium histolyticum did not bind. The affinity ligand was designed according to the formalism proposed by Holmquist and Vallee [Holmquist, B., & Vallee, B. L. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 6216] that effective metalloenzyme inhibitors can be synthesized by coupling a suitable metal-coordinating group to a substrate analogue. In this case, the hydroxamic acid probably coordinates to the active-site metal and the Pro-Leu-Gly moiety is similar to the carboxyl side of the cleavage site of collagen, the enzyme's substrate. The IC50 for N-(benzyloxycarbonyl)-Pro-Leu-Gly-NHOH is 4 X 10(-5) M for both enzymes. The affinity chromatographic procedures described here should aid in future studies on vertebrate collagenases.     

A targeted mutation at the known collagenase cleavage site in mouse type I collagen impairs tissue remodeling

Degradation of type I collagen, the most abundant collagen, is initiated by collagenase cleavage at a highly conserved site between Gly775 and Ile776 of the alpha 1 (I) chain. Mutations at or around this site render type I collagen resistant to collagenase digestion in vitro. We show here that mice carrying a collagenase-resistant mutant Col1a-1 transgene die late in embryo-genesis, ascribable to overexpression of the transgene, since the same mutation introduced into the endogenous Col1a-1 gene by gene targeting permitted normal development of mutant mice to young adulthood. With increasing age, animals carrying the targeted mutation developed marked fibrosis of the dermis similar to that in human scleroderma. Postpartum involution of the uterus in the mutant mice was also impaired, with persistence of collagenous nodules in the uterine wall. Although type I collagen from the homozygous mutant mice was resistant to cleavage by human or rat fibroblast collagenases at the helical site, only the rat collagenase cleaved collagen trimers at an additional, novel site in the nonhelical N-telopeptide domain. Our results suggest that cleavage by murine collagenase at the N-telopeptide site could account for resorption of type I collagen during embryonic and early adult life. During intense collagen resorption, however, such as in the immediate postpartum uterus and in the dermis later in life, cleavage at the helical site is essential for normal collagen turnover. Thus, type I collagen is degraded by at least two differentially controlled mechanisms involving collagenases with distinct, but overlapping, substrate specificities.     

Identification of metal ligands in the Clostridium histolyticum ColH collagenase

A Clostridium histolyticum 116-kDa collagenase has an H415EXXH motif but not the third zinc ligand, as found in already characterized zinc metalloproteinases. To identify its catalytic site, we mutated the codons corresponding to the three conserved residues in the motif to other amino acid residues. The mutation affecting His415 or His419 abolished catalytic activity and zinc binding, while that affecting Glu416 did the former but not the latter. These results suggest that the motif forms the catalytic site. We also mutated the codons corresponding to other amino acid residues that are likely zinc ligands. The mutation affecting Glu447 decreased markedly both the enzymatic activity and the zinc content, while that affecting Glu446 or Glu451 had smaller effects on activity and zinc binding. These mutations caused a decrease in kcat but no significant change in Km. These results are consistent with the hypothesis that Glu447 is the third zinc ligand. The spacing of the three zinc ligands is the same in all known clostridial collagenases but not in other known gluzincins, indicating that they form a new gluzincin subfamily. The effects of mutations affecting Glu446 and Glu451 suggest that the two residues are also involved in catalysis, possibly through an interaction with the two zinc-binding histidine residues.     

A simple method for calibrating collagenase/pronase E ratio to optimize heart cell isolation

Summary— A mixture of crude collagenase and non-specific proteases has been used to isolate guinea pig ventricular heart cells. Measurements of collagenase activity with Wünsch's substrate and protein content with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) suggest that collagenase enzymes do not play a major role in heart cell isolation. On the other hand, an important factor in heart digestion seems to consist of some fractions of the proteases present in crude collagenase. It is also noted that crude collagenases do not present any sensitivity to added calcium but because this ion is important to obtain isolated cells its role is discussed. According to our results, the SDS-PAGE method can be used to determine the appropriate enzyme concentrations to obtain calcium-tolerant myocytes. These myocytes have electrophysiological properties as reported in the literature.     

Development of a Förster resonance energy transfer assay for monitoring bacterial collagenase triple-helical peptidase activity

Due to their efficiency in the hydrolysis of the collagen triple helix, Clostridium histolyticum collagenases are used for isolation of cells from various tissues, including isolation of the human pancreatic islets. However, the instability of clostridial collagenase I (Col G) results in a degraded Col G that has weak collagenolytic activity and an adverse effect on islet isolation and viability. A Förster resonance energy transfer triple-helical peptide substrate (fTHP) has been developed for selective evaluation of bacterial collagenase activity. The fTHP [sequence: Gly-mep-Flp-(Gly-Pro-Hyp)₄-Gly-Lys(Mca)-Thr-Gly-Pro-Leu-Gly-Pro-Pro-Gly-Lys(Dnp)-Ser-(Gly-Pro-Hyp)₄-NH₂] had a melting temperature (T_m) of 36.2 °C and was hydrolyzed efficiently by bacterial collagenase (k_cat/K_M = 25,000 s⁻¹ M⁻¹) but not by clostripain, trypsin, neutral protease, thermolysin, or elastase. The fTHP bacterial collagenase assay allows for rapid and specific assessment of enzyme activity toward triple helices and, thus, potential application for evaluating the efficiency of cell isolation by collagenases.     

Effect of divalent metal ions on collagenase from Clostridium histolyticum.

The collagenase from Clostridium histolyticum (EC 3.4.24.3) degrades type IV collagen with Km 32 nM, indicating a high affinity for this substrate. Ferrous and ferric ions can inhibit Clostridium collagenase. Inhibition by Fe++ was of the mixed, non-competitive type, with Ki 90 microM. The inhibitory effect of Fe++ may be due to Zn++ displacement from the intrinsic functional center of this metalloprotease, since in the presence of excess amounts of Zn++ enzyme activity is retained. This inhibitory effect of Fe++ may be common for all types of collagenases, since this ion can also inhibit type IV collagenase purified from Walker 256 carcinoma, with IC50 80 microM. Cu++ can only partially inhibit Clostridium collagenase, while other divalent metal ions such as Cd++, Co++, Hg++, Mg++, Ni++ or Zn++ are devoid of any inhibitory effect on the enzyme.     

Structural properties of a collagenous heterotrimer that mimics the collagenase cleavage site of collagen type I

Collagens contain sequence- and conformation-dependent epitopes responsible for their digestion by collagenases at specific loci. A synthetic heterotrimer construct containing the collagenase cleavage site of collagen type I was found to mimic perfectly native collagen in terms of selectivity and mode of enzymatic degradation. The NMR conformational analysis of this molecule clearly revealed the presence of two structural domains, i.e. a triple helix spanning the Gly-Pro-Hyp repeats and a less ordered portion corresponding to the collagenase cleavage site where the three chains are aligned in extended conformation with loose interchain contacts. These structural properties allow for additional insights into the very particular mechanism of collagen digestion by collagenases.     

Differences in the degradation of native collagen by two microbial collagenases.

The early stages of degradation of native collagen by two bacterial collagenases were studied by electron microscopy and by automatic Edman degradation. The purified collagenase from Clostridium histolyticum was shown to cleave native collagen at several sites, but not progressively from the N-terminus, as had been previously suggested. The homogeneous collagenase from Achromobacter iophagus cleaves native collagen preferentially at two sites corresponding to the interbands 33-34 and 41-42. The latter lies within the region cleaved by the eukaryotic collagenases.     

The interaction of α2-macroglobulin with proteinases. Binding and inhibition of mammalian collagenases and other metal proteinases

1. Experiments were performed to determine whether the specific collagenases and other metal proteinases are bound and inhibited by alpha(2)-macroglobulin, as are endopeptidases of other classes. 2. A specific collagenase from rabbit synovial cells was inhibited by human serum. The inhibition could be attributed entirely to alpha(2)-macroglobulin; alpha(1)-trypsin inhibitor was not inhibitory. alpha(2)-Macroglobulin presaturated with trypsin or cathepsin B1 did not inhibit collagenase, and pretreatment of alpha(2)-macroglobulin with collagenase prevented subsequent reaction with trypsin. The binding of collagenase by alpha(2)-macroglobulin was not reversible in gel chromatography. 3. The collagenolytic activity of several rheumatoid synovial fluids was completely inhibited by incubation of the fluids with alpha(2)-macroglobulin. 4. The collagenase of human polymorphonuclear-leucocyte granules showed time-dependent inhibition by alpha(2)-macroglobulin. 5. The collagenolytic metal proteinase of Crotalus atrox venom was inhibited by alpha(2)-macroglobulin. 6. The collagenase of Clostridium histolyticum was bound by alpha(2)-macroglobulin, and inhibited more strongly with respect to collagen than with respect to a peptide substrate. 7. Thermolysin, the metal proteinase of Bacillus thermoproteolyticus, was bound and inhibited by alpha(2)-macroglobulin. 8. It was shown by polyacrylamidegel electrophoresis of reduced alpha(2)-macroglobulin in the presence of sodium dodecyl sulphate that synovial-cell collagenase, clostridial collagenase and thermolysin cleave the quarter subunit of alpha(2)-macroglobulin near its mid-point, as do serine proteinases. 9. The results are discussed in relation to previous work, and it is concluded that the characteristics of interaction of the metal proteinases with alpha(2)-macroglobulin are the same as those of other proteinases.     

Age-related changes in collagenase expression in cultured embryonic and fetal human skin fibroblasts

Since skin collagenase is required for initiation of the degradation of types I and III collagens, the major collagens of the human dermis, we examined its expression during embryonic and fetal development. When using skin fibroblasts cultured from human embryos and fetuses, immunoreactive collagenase concentrations were strongly correlated with estimated gestational age (p less than 0.001), with levels at 7-8 weeks of gestation that were about one-twentieth of those in the 29-week cell cultures. In crude culture medium, the apparent catalytic efficiency (activity per unit immunoreactive protein) was variable, an observation attributable in part to variable expression of a collagenase-inhibitory protein. Following chromatographic purification, four of ten fetal collagenases were found to have greater than or equal to 4-fold decrease in specific activity, suggesting that these particular fetal collagenases may be structurally and/or catalytically altered. Since the decreased levels of immunoreactive protein suggested that decreased enzyme synthesis was the major mechanism, we examined collagenase synthesis in a cell-free translation system. Here, we quantitated collagenase expression in the culture medium of intact cells prior to harvesting mRNA. Compared with the intact adult cells, the fetal cells had 3-17 times less collagenase activity in the medium, while in cell-free translation there was a 2- to 3-fold decrease in collagenase synthesis. These data suggest that decreased in vitro expression is correlated with decreased levels of translatable collagenase mRNA but that other factors, such as the collagenase inhibitor and altered specific activity of the enzyme, may be important in modulating collagenase activity.