Recognition and catabolism of synthetic heterotrimeric collagen peptides by matrix metalloproteinases

BACKGROUND: The general consensus is that interstitial collagens are digested by collagenases and denatured collagen by gelatinases, although processing of fibrillar and acetic-acid-soluble collagen by gelatinase A has also been reported. One of the main difficulties in studying the mechanism of action of these matrix metalloproteinases (MMPs) derives from the physicochemical properties of the natural triple-helical collagen, which makes it difficult to handle. RESULTS: Synthetic heterotrimeric collagenous peptides that contain the collagenase cleavage site of human collagen type I and differ in the thermal stability of the triple-helical fold were used to mimic natural collagen and gelatin, respectively. Results from digestion of these substrates by fibroblast and neutrophil collagenases (MMP-1 and MMP-8), as well as by gelatinase A (MMP-2), confirmed that the two classes of enzymes operate within the context of strong conformational dependency of the substrates. It was also found that gelatinases and collagenases exhibit two distinct proteolytic mechanisms: gelatinase digests the gelatin-like heterotrimer rapidly in individual steps with intermediate releases of partially processed substrate into the medium, whereas collagenases degrade the triple-helical heterotrimer by trapping it until scission through all three alpha chains is achieved. CONCLUSIONS: The results confirm the usefulness of synthetic heterotrimeric collagenous peptides in the folded and unfolded state as mimics of the natural substrates collagen and gelatin, respectively, to gain a better a insight into the proteolytic mechanisms of matrix metalloproteinases.     

Controlling the morphology of metal-promoted higher ordered assemblies of collagen peptides with varied core lengths

Self-assembling peptides have become an important subclass of next-generation biomaterials. In particular, materials that mimic the properties of collagen have received considerable attention due to the unique properties of natural collagen. Previous peptide-based designs have been successful in generating structures with morphological properties that were primarily determined by the type of self-assembling mechanism. Herein we demonstrate the metal ion-promoted, supramolecular assembly of collagen-based peptide triple helices into distinct morphologies that are controlled by defining the number of Pro-Hyp-Gly repeating units. We synthesized and characterized collagen-based peptides that incorporated either 5, 7, 9, or 11 Pro-Hyp-Gly repeating units. We found that the number of repeating units, and the resulting stability of the collagen triple helix, is intimately linked with the types of assemblies formed. For instance, collagen peptides that did not form a stable triple helix, such as NCoH5, did not participate in supramolecular assembly with added metal ions. Collagen peptides that formed stable triple helices, such as NCoH11, resulted in microsaddle structures with metal-promoted assembly, whereas a highly cross-linked, three-dimensional mesh formed with NCoH7, albeit at a higher metal ion concentration. These data provide evidence that triple helix formation is required for efficient metal-triggered assembly to the observed microstructures.     

Facile modification of collagen directed by collagen mimetic peptides

Recent widespread interest in the development of engineered tissue and organ replacement therapies has prompted demand for new approaches to immobilize exogenous components to natural collagen. Chemical coupling of synthetic moieties to amino acid side chains has been commonly practiced for such purposes; however, such coupling reactions are difficult to control on large proteins and are generally not conducive to modifying integrated collagen scaffolds that contain live cells and tissues. As an alternative to the conventional "covalent" modification method, we have developed a novel "physical" modification technique that is based on collagen's native ability to associate into a triple-helical molecular architecture. Here, we present a finding that collagen mimetic peptides (CMPs) of sequence -(Pro-Hyp-Gly)x- exhibit strong affinity to both native and gelatinized type I collagen under controlled thermal conditions. We also show that the cell adhesion characteristics of collagen can be readily altered by applying a poly(ethylene glycol)-CMP conjugate to a prefabricated collagen film.     

Open-tubular electrochromatographic characterization of synthetic peptides

The open-tubular electrochromatographic (OT-CEC) migration behavior of a series of peptides, based on a common structural feature, has been characterized using two different types of chemically modified etched capillaries. The organic moieties immobilized onto the capillary inner surface were n-butylphenyl and cholesterol-10-undecenaoate, respectively. The structure-migration behavior of this set of peptides has been studied at several pH values and with methanol at different concentrations as an organic solvent modifier of the buffer electrolyte composition. By comparing the structural properties of the peptides, such as their amino acid sequences, charge-to-mass ratios and intrinsic hydrophobicities to their migrational behavior, the relative contribution of electrophoretic and chromatographic mobility to the overall migration times, elution order, and selectivity has been determined. Moreover, the experimental data provide important insight into procedures that can be used to modulate the separation of peptides in OT-CEC through variation of the composition of the electrolyte buffer as well as via the properties of the bonded organic moiety.     

Design of synthetic peptides for diagnostics

Due to the advantageous properties of synthetic molecules compared to biological ones biological molecules in diagnostic tests are replaced increasingly by synthetic ones, usually synthetic peptides or related molecules. The replacement of biological antigens by synthetic peptides is most advanced at present, as well as the use of site-specific antibodies induced with synthetic peptides. Moreover recent results indicate that synthetic molecules may also replace antibodies. Ultimately this will lead to diagnostic assays built of synthetic molecules only.     

Photoelectrochemical immunodiagnosis of canine leishmaniasis using cadmium-sulfide-sensitized zinc oxide modified with synthetic peptides

A photoelectrochemical immunosensor for the detection of anti-Leishmania infantum antibodies based on zinc oxide and cadmium sulfide films electrodeposited on an ITO-coated glass slide (CdS/ZnO/ITO) has been proposed. The effects of light/dark conditions and the kinetics of CdS sensitizer regeneration were evaluated by scanning electrochemical microscopy in feedback mode. The platform was modified using two different peptides (PEP 13 and PEP 16) from two different proteins of high specificity and selectivity toward recognition of L. infantum antibodies, producing Peps/CdS/ZnO/ITO. This photoelectrochemical immunosensor provides a cheap and promising method of discriminating between positive and negative canine serum samples.     

Immunodiagnosis of parasitic diseases with synthetic peptides

Parasitic diseases remain as a major public health problem worldwide, not only based on their historically high morbidity and mortality rates, but also because risk factors associated with their transmission are increasing. Laboratory diagnosis and particularly immunodiagnosis is a basic tool for the demonstration, clinical management and control of these infections. Classically, the serological tests for the detection of antibodies or antigens are based on the use of crude and purified antigens. Synthetic peptides have opened a new field and perspectives, as the source of pure epitopes and molecules for diagnosis of malaria, Chagas' disease, leishmaniasis, schistosomiasis, hidatidosis, cysticercosis and fasciolosis based on the detection of antibodies and circulating antigens. Herein, are critically reviewed the relevant advances and applications of the synthetic peptides on immunodiagnosis of parasitic diseases. A variety of sequences, constructs (monomers, polymers, MAPs), immunological methods and samples have been used, demonstrating their diagnostic potential. However, in most parasitic infections it is necessary to use more than a single peptide in order to avoid the genetic restriction against certain epitopes, as well as to test them in well characteized groups of patients, in order to confirm their sensitivity and specificity. The concept of multidiagnosis with synthetic peptides, using a novel multi-dot blot assay is introduced. Finally, the chemical imitation of antigens, offers a tremendous posibilities in the diagnosis of parasitic infections in developing countries since this strategy is cheaper, simpler, reproducible, useful for large scale testing and in most cases, specific and sensitive.     

Molecular assembly of Zn porphyrin complexes onto a gold electrode using synthetic light-harvesting model polypeptides

Molecular assembly of Zn porphyrin pigments, Zn substituted bacteriochlorophyll a ([Zn]-BChl a) and Zn mesoporphyrin monomer (ZnMPMME) on a gold electrode using synthetic 1α-helix hydrophobic polypeptides which have similar amino acid sequences to the hydrophobic core in the native photosynthetic light-harvesting (LH) 1-β polypeptide from Rhodobacter sphaeroides, has been achieved: this process is dependent on the structures of pigments and polypeptides. Interestingly, an enhanced photoelectric current was observed when ZnMPMME with the LH1 model polypeptide in an α-helical configuration was assembled onto the electrode.     

Separations of hydrophobic synthetic peptides in counter-current chromatography

Synthetic peptides with many aromatic, aliphatic and especially acidic amino acid residues are not very soluble and require strong solvents for useful partitioning. A chloroform-methanol-acidic solvent system fractionates neutral and basically charged 26-mers to provide high yields. An insoluble 15-mer with 5 Trp residues and 60% overall hydrophobic amino acid content was purified in pyridine-acetic acid and in another basic t-butyl methyl ether-n-butanol-acetonitrile solvent system with high recovery. Two instruments were used, the eccentric-multi-layer hybrid coil planet centrifuge and the new spiral disk planet centrifuge that were able to retain the stationary phase of these solvent systems, some of which have low interfacial tension.     

Epitaxially guided assembly of collagen layers on mica surfaces

Ordered assembly of collagen molecules on flat substrates has potential for various applications and serves as a model system for studying the assembly process. While previous studies demonstrated self-assembly of collagen on muscovite mica into highly ordered layers, the mechanism by which different conditions affect the resulting morphology remains to be elucidated. Using atomic force microscopy, we follow the assembly of collagen on muscovite mica at a concentration lower than the critical fibrillogenesis concentration in bulk. Initially, individual collagen molecules adsorb to mica and subsequently nucleate into fibrils possessing the 67 nm D-periodic bands. Emergence of fibrils aligned in parallel despite large interfibril distances agrees with an alignment mechanism guided by the underlying mica. The epitaxial growth was further confirmed by the formation of novel triangular networks of collagen fibrils on phlogopite mica, whose surface lattice is known to have a hexagonal symmetry, whereas the more widely used muscovite does not. Comparing collagen assembly on the two types of mica at different potassium concentrations revealed that potassium binds to the negatively charged mica surface and neutralizes it, thereby reducing the binding affinity of collagen and enhancing surface diffusion. These results suggest that collagen assembly on mica follows the surface adsorption, diffusion, nucleation, and growth pathway, where the growth direction is determined at the nucleation step. Comparison with other molecules that assemble similarly on mica supports generality of the proposed assembly mechanism, the knowledge of which will be useful for controlling the resulting surface morphologies.     

Noncovalent multivalent assembly of jun peptides on a leucine zipper dendrimer displaying fos peptides

[reaction: see text] The synthesis and characterization of a new leucine-zipper dendrimer (LZD) is reported that displays four copies of the peptide corresponding to the coiled-coiled dimerization domain of Fos. Circular dichroism spectroscopy, fluorescence titration, and sedimentation equilibrium experiments demonstrate that Fos-LZD can noncovalently assemble four copies of the peptide corresponding to the coiled-coil domain of Jun. This work provides the basis for the future construction of noncovalently assembled multivalent protein assemblies displaying any protein of interest.     

Improved mass accuracy for higher mass peptides by using SWIFT excitation for MALDI-FTICR mass spectrometry

Stepwise-external calibration has previously been shown to produce sub part-per-million (ppm) mass accuracy for the MALDI-FTICR/MS analyses of peptides up to m/z 2500. The present work extends these results to ions up to m/z 4000. Mass measurement errors for ions of higher mass-to-charge are larger than for ions below m/z 2500 when using conventional chirp excitation to detect ions. Mass accuracy obtained by using stored waveform inverse Fourier transform (SWIFT) excitation was evaluated and compared with chirp excitation. Analysis of measurement errors reveals that SWIFT excitation provides smaller deviations from the calibration equation and better mass accuracy than chirp excitation for a wide mass range and for widely varying ion populations.     

NMR monitoring of chain-specific stability in heterotrimeric collagen peptides

NMR spectroscopy is used to investigate the heterotrimeric nature of a collagen model peptide. Two distinct peptide chains (A and B) were synthesized to model a site in heterotrimeric basement membrane type IV collagen. For NMR studies, four amino acids in the B chain were labeled with 15N/13C. Circular dichroism spectroscopy and differential scanning calorimetry thermal stability results on a solution with both A and B peptides (molar ratio 2A:1B) are consistent with the presence of one heterotrimeric triple-helical molecular species. Heteronuclear single quantum coherence experiments on homotrimers of the B peptide show trimer peaks which disappear at temperatures higher than 10 degrees C, while the 2A:1B mixture has trimer peaks with increased stability and altered chemical shifts. The reduction in the number of Leu trimer peaks from three to one and the increased stability of trimer resonances confirm the participation of B chains in an AAB heterotrimer molecule.     

Specific activity of collagenase on peptides related to collagen

Summary The relative rate of cleavage by collagenase of three new synthetic substrates-(glycyl-prolyl-alanine)₂, (glycyl-prolyl-glycine)₂, and (glycyl-prolyl-hydroxyproline)₂-has been studied. These substrates, which simulate the amino acid sequences within the pseudocrystalline zones of collagen, are cleaved by collagenase at different rates.     

Metal-mediated tandem coassembly of collagen peptides into banded microstructures

The ability to recapitulate the features of natural collagen at the micro- and nanoscale with novel biopolymers has the potential to lead to improved biomaterials. Herein we describe stimuli-responsive collagen-based peptides (IdaCol and HisCol) that together form higher order assemblies in the presence of added metal ions. SEM and TEM imaging of these assemblies revealed microscale petal-like and intertwined fiber morphologies, each with periodic banding on the nanometer scale. The observed banding is consistent with tandem coassembly of alternating IdaCol and HisCol triple helical blocks that may laterally associate either in or out of register to form higher order structures, and mimics the banding found in natural collagen fibers.     

Rational design and assembly of synthetic trimodular polyketide synthases

Type I polyketide synthases (PKSs) consist of modules that add two-carbon units in polyketide backbones. Rearranging modules from different sources can yield novel enzymes that produce unnatural products, but the rules that govern module-module communication are still not well known. The construction and assay of hybrid bimodular units with synthetic PKS genes were recently reported. Here, we describe the rational design of trimodular PKSs by combining bimodular units. A cloning-expression system was developed to assemble and test 54 unnatural trimodular PKSs flanked by the loading module and the thioesterase from the erythromycin synthase. Remarkably, 96% of them produced the expected polyketide. The obtained results represent an important milestone toward the ultimate goal of making new bioactive polyketides by rational design. Additionally, these results show a path for the production of customized tetraketides by fermentation, which can be an important source of advanced intermediates to facilitate the synthesis of complex products.