The primary structure of collagen

Collagen as the extracellular matrix biomaterials in the arena of medical sciences

Collagen is a multipurpose material that has several applications in the health care, dental care, and pharmaceutical industries. Crosslinked compacted solids or lattice-like gels can be made from collagen. Biocompatibility, biodegradability, and wound-healing properties make collagen a popular scaffold material for cardiovascular, dentistry, and bone tissue engineering. Due to its essential role in the control of several of these processes, collagen has been employed as a wound-healing adjunct. It forms a major component of the extracellular matrix and regulates wound healing in its fibrillar or soluble forms. Collagen supports cardiovascular and other soft tissues. Oral wounds have been dressed with resorbable forms of collagen for closure of graft and extraction sites, and to aid healing. This present review is concentrated on the use of collagen in bone regeneration, wound healing, cardiovascular tissue engineering, and dentistry.

A fresh perspective on infrared spectroscopy as a prescreening method for molecular and stable isotopes analyses on ancient human bones

Following the development of modern genome sequencing technologies, the investigation of museum osteological finds is increasingly informative and popular. Viable protocols to help preserve these collections from exceedingly invasive analyses, would allow greater access to the specimens for scientific research. The main aim of this work is to survey skeletal tissues, specifically petrous bones and roots of teeth, using infrared spectroscopy as a prescreening method to assess the bone quality for molecular analyses. This approach could overcome the major problem of identifying useful genetic material in archaeological bone collections without resorting to demanding, time consuming and expensive laboratory studies. A minimally invasive sampling of archaeological bones was developed and bone structural and compositional changes were examined, linking isotopic and genetic data to infrared spectra. The predictive model based on Infrared parameters is effective in determining the occurrence of ancient DNA (aDNA); however, the quality/quantity of aDNA cannot be determined because of the influence of environmental and local factors experienced by the examined bones during the burial period.

Collagen fabricated delivery systems for wound healing: A new roadmap

Collagen is a biopolymer found in the animal body. It is one of the most abundant proteins in the extracellular matrix that provides strength to the skin, joints, and bones in the human body. It is an important source of elasticity and strength in the extracellular matrix and contributes to the structural and physiological integrity of tissues. Collagen plays an important role in regulating the wound healing process. It helps in wound healing by attracting fibroblasts and encouraging new collagen formation in the wound bed. Therefore, it can be used as a supplementary aid for wound treatment to accelerate the healing process. A prominent benefit of incorporating collagen in wound dressings is its ability to enhance the healing process for critical wounds. Not only collagen but various collagen-containing systems are being prepared to boost its efficacy in wound healing. Different strategies like nanoscale reductions, biopolymers, and incorporating anti-inflammatory and antimicrobial drugs with collagen have been reported. This review article emphasizes the use of collagen for wound healing and various collagen fabricated delivery systems such as nanofibres, nanoparticles, hydrogels, films, and sponges that aid in the healing of wounds.

Identification and Characterization of Fibronectin-Binding Peptides in Gelatin

Collagen and fibronectin (FN) are important components in the extracellular matrix (ECM). Collagen-FN binding belongs to protein-protein interaction and plays a key role in regulating cell behaviors. In this study, FN-binding peptides were isolated from gelatin (degraded collagen) using affinity chromatography, and the amino acid sequences were determined using HPLC-MS. The results indicated that all FN-binding peptides contained GPAG or GPPG. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and dual-polarization interferometry (DPI) were used to analyze the effects of hydroxylation polypeptide on FN binding activity. DPI analysis indicated that peptides with molecular weight (MW) between 2 kDa and 30 kDa showed higher FN-binding activity, indicating MW range played an important role in the interaction between FN and peptides. Finally, two peptides with similar sequences except for hydroxylation of prolines were synthesized. The FN-binding properties of the synthesized peptides were determined by MALDI-TOF MS. For peptide, GAPGADGP*AGAPGTP*GPQGIAGQR, hydroxylation of P8 and P15 is necessary for FN-binding. For peptide, GPPGPMGPPGLAGPPGESGR, the FN-binding process is independent of proline hydroxylation. Thus, FN-binding properties are proline-hydroxylation dependent.

Lung Mechanics Over the Century: From Bench to Bedside and Back to Bench

Lung physiology research advanced significantly over the last 100 years. Respiratory mechanics applied to animal models of lung disease extended the knowledge of the workings of respiratory system. In human research, a better understanding of respiratory mechanics has contributed to development of mechanical ventilators. In this review, we explore the use of respiratory mechanics in basic science to investigate asthma and chronic obstructive pulmonary disease (COPD). We also discuss the use of lung mechanics in clinical care and its role on the development of modern mechanical ventilators. Additionally, we analyse some bench-developed technologies that are not in widespread use in the present but can become part of the clinical arsenal in the future. Finally, we explore some of the difficult questions that intensive care doctors still face when managing respiratory failure. Bringing back these questions to bench can help to solve them. Interaction between basic and translational science and human subject investigation can be very rewarding, as in the conceptualization of “Lung Protective Ventilation” principles. We expect this interaction to expand further generating new treatments and managing strategies for patients with respiratory disease.

Segment-Long-Spacing (SLS) and the Polymorphic Structures of Fibrillar Collagen

The diverse and complex functions of collagen during the development of an organism are closely related to the polymorphism of its supramolecular structures in the extracellular matrix. SLS (segment-long-spacing) is one of the best understood alternative structures of collagen. SLS played an instrumental role in the original studies of collagen more than half a century ago that laid the foundation of nearly everything we know about collagen today. Despite being used mostly under in vitro conditions, the natural occurrence of SLS in tissues has also been reported. Here we will provide a brief overview of the major findings of the SLS and other structures of collagen based on a wealth of work published starting from the 1940s. We will discuss the factors that determine the stability and the structural specificity of the different molecular assemblies of collagen in light of the new studies using designed fibril forming collagen peptides. At the end of the chapter, we will summarize some recent discoveries of the alternative structures of collagen in tissues, especially those involved in pathogenic states. A revisit of SLS will likely inspire new understandings concerning the range of critical roles of fibrillar collagen in terms of its organizational diversity in the extracellular matrix.

Trends in deamidation across archaeological bones, ceramics and dental calculus

The accumulation of post-translational modifications (PTMs) in proteins throughout the lifecycle has been studied for decades, particularly more so with the advent of soft-ionization mass spectrometry-based proteomic techniques. However, particular PTMs, such as the deamidations of asparagine and glutamine residues, continue to accumulate in proteins that remain into the forensic, archaeological, and palaeontological records. The accurate measurement of these ancient 'molecular timers' has been proposed as a method to not only differentiate between exogenous and endogenous proteins within complex mixtures (i.e., contamination), but also as a method of providing relative age estimations into geological time. In this study we explored the extent to which deamidation varies with chronological age across different proteins in bones, as well as investigated differences between proteins across dental calculus and archaeological ceramics. We also analysed the relationships between the observed extent of deamidation and the protein primary structure. We found that collagen obtained from archaeological bones showed a chronological dependence on the extent of deamidation observed, but only when they were from similar environments, supporting prior suggestions about 'thermal age' being a major influence on the deamidation observed. Our study on non-collagenous proteins (NCPs) in archaeological bones showed that while biglycan, and to a lesser extent chondroadherin, showed positive correlations between geological age and the extent of deamidation, others including fetuin-A and serum albumin did not. However, despite the well-known dependence of deamidation on the three-dimensional structure of the peptides, we were unable to find any clear correlation between the structural motifs of the peptides in archaeological bones and the extent of deamidation observed. Our analysis of a set of food proteins obtained from Neolithic archaeological ceramics in Çatalhöyük also showed similar deamidation levels irrespective of the protein structure. Overall, our results suggest that deamidation in archaeological samples could be useful for obtaining additional information beyond identification of species and tissue type, be that as a measure of protein endogeneity and potential contamination, or a measure of protein degradation, or as an indicator of thermal age and for relative dating; however, further research needs to be undertaken to understand why particular proteins are better for this than others, going beyond simple consideration of their secondary structure.

Glycosylation of Type I Collagen

Fibrillar type I collagen is the most abundant structural protein in most tissues and organs. One of the unique and functionally important characteristics of collagen is sequential posttranslational modifications of lysine (Lys) residues. In the endoplasmic reticulum, hydroxylation of specific Lys occurs producing 5-hydroxylysine (Hyl). Then, to the 5-hydroxyl group of Hyl, a single galactose unit can be attached to form galactosyl-Hyl (Gal-Hyl) and further glucose can be added to Gal-Hyl to form glucosylgalactosyl-Hyl (GlcGal-Hyl). These are the only two O-linked glycosides found in mature type I collagen. It has been shown that this modification is critically involved in a number of biological and pathological processes likely through its regulatory roles in collagen fibrillogenesis, intermolecular cross-linking, and collagen-cell interaction. Recently, with the advances in molecular/cell biology and analytical chemistry, the molecular mechanisms of collagen glycosylation have been gradually deciphered, and the type and extent of glycosylation at the specific molecular loci can now be quantitatively analyzed. In this chapter, we describe quantitative analysis of collagen glycosylation by high-performance liquid chromatography (HPLC) and semiquantitative, site-specific analysis by HPLC-tandem mass spectrometry.

Identifying a novel role for X-prolyl aminopeptidase (Xpnpep) 2 in CrVI-induced adverse effects on germ cell nest breakdown and follicle development in rats

Environmental exposure to endocrine-disrupting chemicals (EDCs) is one cause of premature ovarian failure (POF). Hexavalent chromium (CrVI) is a heavy metal EDC widely used in more than 50 industries, including chrome plating, welding, wood processing, and tanneries. Recent data from U.S. Environmental Protection Agency indicate increased levels of Cr in drinking water from several American cities, which potentially predispose residents to various health problems. Recently, we demonstrated that gestational exposure to CrVI caused POF in F1 offspring. The current study was performed to identify the molecular mechanism behind CrVI-induced POF. Pregnant rats were treated with 25 ppm of potassium dichromate from Gestational Day (GD) 9.5 to GD 14.5 through drinking water, and the fetuses were exposed to CrVI through transplacental transfer. Ovaries were removed from the fetuses or pups on Embryonic Day (ED) 15.5, ED 17.5, Postnatal Day (PND) 1, PND 4, or PND 25, and various analyses were performed. Results showed that gestational exposure to CrVI: 1) increased germ cell/oocyte apoptosis and advanced germ cell nest (GCN) breakdown; 2) increased X-prolyl aminopeptidase (Xpnpep) 2, a POF marker in humans, during GCN breakdown; 3) decreased Xpnpep2 during postnatal follicle development; and 4) increased colocalization of Xpnpep2 with Col3 and Col4. We also found that Xpnpep2 inversely regulated the expression of Col1, Col3, and Col4 in all the developmental stages studied. Thus, CrVI advanced GCN breakdown and increased follicle atresia in F1 female progeny by targeting Xpnpep2.

Consequences of irradiation on bone and marrow phenotypes, and its relation to disruption of hematopoietic precursors

The rising levels of radiation exposure, specifically for medical treatments and accidental exposures, have added great concern for the long term risks of bone fractures. Both the bone marrow and bone architecture are devastated following radiation exposure. Even sub-lethal doses cause a deficit to the bone marrow microenvironment, including a decline in hematopoietic cells, and this deficit occurs in a dose dependent fashion. Certain cell phenotypes though are more susceptible to radiation damage, with mesenchymal stem cells being more resilient than the hematopoietic stem cells. The decline in total bone marrow hematopoietic cells is accompanied with elevated adipocytes into the marrow cavity, thereby inhibiting hematopoiesis and recovery of the bone marrow microenvironment. Poor bone marrow is also associated with a decline in bone architectural quality. Therefore, the ability to maintain the bone marrow microenvironment would hinder much of the trabecular bone loss caused by radiation exposure, ultimately decreasing some comorbidities in patients exposed to radiation.

Enzyme-mediated proteolysis of fibrous biopolymers: Dissolution front movement in fibrin or collagen under conditions of diffusive or convective transport

A numerical model based on the convective-diffusive transport of reacting and adsorbing proteolytic enzymes within erodible fibrous biopolymers was used to predict lysis fronts moving across biogels such as fibrin or collagen. The fiber structure and the transport properties of solutes in fibrin (or collagen) were related to the local extent of dissolution within the dissolving structure. An accounting for solubilization of adsorbed species into solution from the eroding fiber phase provided for complete conservation of mass in reacting systems containing over 10 species. At conditions of fibrinolysis typical of clinical situations, the model accurately predicted the dynamic rate of lysis front movement for plasmin, urokinase, and tissue plasminogen activator (tPA)-mediated lysis of fibrin gels measured in vitro. However, under conditions of extremely fast fibrinolysis using high enzyme concentrations, fibrinolytic fronts moved very rapidly (>0.1 mm/mm)-faster than predicted for diffusionlimited reactions-at nearly constant velocity for over 2 h, indicating non-Fickian behavior. This was due to proteolysis-mediated retraction of dissolving fibrin fibers that resulted in fiber convection and front-sharpening within 3 mum of the reaction front, as observed by digitally enhanced microscopy. In comparing the model to fibrinolysis measurements using human lys(77)-plasmin, the average first order rate constant for non-crosslinked fibrin bond cleavage by fibrin-bound plasmin was calculated to be 5s(-1) assuming that 10 cleavages per fibrin monomer were required to solubilize each monomer. The model accurately predicted lysis front movement using pressure-driven permeation of plasmin or urokinase into fibrin as well as literature data obtained under well- mixed conditions for tPA-mediated fibrinolysis. This numerical formulation provides predictive capability for optimization of proteolytic systems which include thrombolytic therapy, wound healing, controlled drug release, and tissue engineering applications. (c) 1995 John Wiley & Sons, Inc.

Lysyl hydroxylase 3-mediated glucosylation in type I collagen: molecular loci and biological significance

Recently, by employing the short hairpin RNA technology, we have generated MC3T3-E1 (MC)-derived clones stably suppressing lysyl hydroxylase 3 (LH3) (short hairpin (Sh) clones) and demonstrated the LH3 function as glucosyltransferase in type I collagen (Sricholpech, M., Perdivara, I., Nagaoka, H., Yokoyama, M., Tomer, K. B., and Yamauchi, M. (2011) Lysyl hydroxylase 3 glucosylates galactosylhydroxylysine residues in type I collagen in osteoblast culture. J. Biol. Chem. 286, 8846-8856). To further elucidate the biological significance of this modification, we characterized and compared type I collagen phenotypes produced by Sh clones and two control groups, MC and those transfected with empty vector. Mass spectrometric analysis identified five glycosylation sites in type I collagen (i.e. α1,2-87, α1,2-174, and α2-219. Of these, the predominant glycosylation site was α1-87, one of the major helical cross-linking sites. In Sh collagen, the abundance of glucosylgalactosylhydroxylysine was significantly decreased at all of the five sites with a concomitant increase in galactosylhydroxylysine at four of these sites. The collagen cross-links were significantly diminished in Sh clones, and, for the major cross-link, dihydroxylysinonorleucine (DHLNL), glucosylgalactosyl-DHLNL was diminished with a concomitant increase in galactosyl-DHLNL. When subjected to in vitro incubation, in Sh clones, the rate of decrease in DHLNL was lower, whereas the rate of increase in its maturational cross-link, pyridinoline, was comparable with controls. Furthermore, in Sh clones, the mean diameters of collagen fibrils were significantly larger, and the onset of mineralized nodule formation was delayed when compared with those of controls. These results indicate that the LH3-mediated glucosylation occurs at the specific molecular loci in the type I collagen molecule and plays critical roles in controlling collagen cross-linking, fibrillogenesis, and mineralization.

Safety of intra-articular use of atelocollagen for enhanced tissue repair

Collagen is an important biomaterial in intra-articular tissue engineering, but there are unanswered questions about its safety. We hypothesize that the addition of type-I-collagen for primary repair of the Anterior Cruciate Ligament (ACL) might result in a local and systemic reaction in a porcine model after 15 weeks as demonstrated by joint effusion, synovial thickening, elevated intraarticular and systemic leukocyte counts. Further, this reaction might be aggravated by the addition of a platelet concentrate. Eighteen porcine ACLs were transected and repaired with either sutures (n=6), a collagen sponge (n=6), or a collagen-platelet-composite (CPC; n=6). Twelve intact contralateral knees served as controls (n=12). No significant synovial thickening or joint effusion was seen in the collagen-treated knees. Synovial fluid leukocyte counts showed no significant differences between surgically treated and intact knees, and no differences were seen in leukocyte counts of the peripheral blood. The addition of a platelet concentrate to the knee joint resulted in lower serum levels of IL-1β, but serum levels of TNF-α were not significantly different between groups. In conclusion, the presence of collagen, with or without added platelets, did not increase the local or systemic inflammatory reactions following surgery, suggesting that Type I collagen is safe to use in the knee joint.

Development of a novel method for analyzing collagen O-glycosylations by hydrazide chemistry

In recent years, glycopeptide purification by hydrazide chemistry has become popular in structural studies of glycoconjugates; however, applications of this method have been almost completely restricted to analysis of the N-glycoproteome. Here we report a novel method for analyzing O-glycosylations unique to collagen, which are attached to hydroxylysine and include galactosyl-hydroxylysine and glucosyl-galactosyl-hydroxylysine. We established a hydrazide chemistry-based glycopeptide purification method using (1) galactose oxidase to introduce an aldehyde into glycopeptides and (2) formic acid with heating to elute the bound glycopeptides by cleaving the hydrazone bond. This method allows not only identification of O-glycosylation sites in collagen but also concurrent discrimination of two types of carbohydrate substitutions. In bovine type I and type II collagens, galactosyl-hydroxylysine /glucosyl-galactosyl-hydroxylysine -containing peptides were specifically detected on subsequent comprehensive liquid chromatography (LC)/MS analysis, and many O-glycosylation sites, including unreported ones, were identified. The position of glycosylated hydroxylysine, which is determined by our unambiguous and simple method, could provide insight into the physiological role of the modifications.

MECHANICAL PROPERTIES OF GREAT ARTERIAL WALL AND CLINICAL IMPLICATION

X-ray diffraction and microscopic analysis investigate the morphological organization of the structural components in the dog carotid wall. Histological analysis confirms an anisotropic morphology of smooth muscle cells and elastic fibers in the tissue. Collagen fibers, as revealed by X-ray diffraction technique, are organized in an isotropic network in the unstretched carotid media. Collagen fibers stretch without a preferential direction of orientation when a carotid segment is deformed in the physiological range under intraluminal pressure. A mathematical model, which takes into account the isotropic distribution of the collagen fibers, is developed. The validity of this model has been tested by computing several mechanical parameters using Anliker's data on the axial and radial oscillation obtained for carotids of living dogs. In spite of the anisotropic morphology of the main constituents of the carotid media layer, from a mechanical point of view the tissue can be considered as an isotropic material for the random distribution of the collagen fibers, which represent the component of higher tensile strength.

Pigment epithelium-derived factor (PEDF) shares binding sites in collagen with heparin/heparan sulfate proteoglycans

Pigment epithelium-derived factor (PEDF) is a collagen-binding protein that is abundantly distributed in various tissues, including the eye. It exhibits various biological functions, such as anti-angiogenic, neurotrophic, and neuroprotective activities. PEDF also interacts with extracellular matrix components such as collagen, heparan sulfate proteoglycans (HSPGs), and hyaluronan. The collagen-binding property has been elucidated to be important for the anti-angiogenic activity in vivo (Hosomichi, J., Yasui, N., Koide, T., Soma, K., and Morita, I. (2005) Biochem. Biophys. Res. Commun. 335, 756-761). Here, we investigated the collagen recognition mechanism by PEDF. We first narrowed down candidate PEDF-binding sequences by taking advantage of previously reported structural requirements in collagen. Subsequent searches for PEDF-binding sequences employing synthetic collagen-like peptides resulted in the identification of one of the critical binding sites for PEDF, human α1(I)(929-938) (IKGHRGFSGL). Further analysis revealed that the collagen recognition by PEDF is sequence- and conformation-specific, and the high affinity binding motif is KGXRGFXGL in the triple helix. The PEDF-binding motif significantly overlapped with the heparin/HSPG-binding motif, KGHRG(F/Y). The interaction of PEDF with collagen I was specifically competed with by heparin but not by chondroitin sulfate-C or hyaluronan. The binding sequences for PEDF and heparin/HSPG also overlapped with the covalent cross-linking sites between collagen molecules. These findings imply a functional relationship between PEDF and HSPGs during angiogenesis, and the interaction of these molecules is regulated by collagen modifications.

Deficiency of cartilage-associated protein in recessive lethal osteogenesis imperfecta

Classic osteogenesis imperfecta, an autosomal dominant disorder associated with osteoporosis and bone fragility, is caused by mutations in the genes for type I collagen. A recessive form of the disorder has long been suspected. Since the loss of cartilage-associated protein (CRTAP), which is required for post-translational prolyl 3-hydroxylation of collagen, causes severe osteoporosis in mice, we investigated whether CRTAP deficiency is associated with recessive osteogenesis imperfecta. Three of 10 children with lethal or severe osteogenesis imperfecta, who did not have a primary collagen defect yet had excess post-translational modification of collagen, were found to have a recessive condition resulting in CRTAP deficiency, suggesting that prolyl 3-hydroxylation of type I collagen is important for bone formation.

Capillary electromigration methods for the study of collagen

This review paper gives an overview of capillary electromigration methods used in the analysis of collagen. Analyses of the parent chains as well as of the bromcyane and collagenase fragments of collagens are presented. Methods include capillary zone electrophoresis, capillary gel electrophoresis, micellar electrokinetic chromatography as well as combinations of HPLC and capillary electrophoresis, and capillary electrophoresis with mass spectrometry.

Impact of collagen subtype proportions in peritoneal tissues on inguinal hernia formation in adults and infants

Impaired collagen subtype proportions in the matrices results in the alteration of tissue tensile strength, and is an underlying cause of adult inguinal hernia formation; however, it remains unclear if this alteration is also responsible for infantile inguinal hernia formation. We correlated the ratios of collagen type I to type III between adults and infants with and those without an inguinal hernia, in an attempt to clarify the pathogenesis of this disorder. We extracted collagen from the hernial sacs of patients with an inguinal hernia, and from the normal peritoneum of patients without an inguinal hernia. After separation by electrophoresis, the collagen bands were quantified and we compared the ratios of collagen type I to type III between the patients with and those without an inguinal hernia. The ratio of collagen type I to type III was significantly lower in the adults with an inguinal hernia (n=8, 6.17+/-2.69) than in those without an inguinal hernia (n=8, 9.38+/-2.99, P=0.041), whereas the ratios were similar in infants with (n=10, 5.72+/-2.66) and those without an inguinal hernia (n=6, 5.60+/-1.88, P=0.925). Our results showed that tissue weakness was not involved in the pathogenesis of infantile inguinal hernia formation, confirming that simple herniotomy is adequate treatment.

Antigenicity and immunogenicity of collagen

Pertinent issues of collagen antigenicity and immunogenicity are concisely reviewed as they relate to the design and application of biomedical devices. A brief discussion of the fundamental concepts of collagen immunochemistry is presented, with a subsequent review of documented clinical responses to devices containing reconstituted soluble or solubilized collagen. The significance of atelocollagen, concerns regarding collagen-induced autoimmunity, and other relevant topics are also addressed in the context of current understanding of the human immune response to collagen.

Cathepsin D: specificity of peptide-bond cleavage in type-I collagen and effects on type-III collagen and procollagen

1. Cathepsin D, purified from bovine thymus, has a limited proteolytic effect on types I and III bovine collagens. The alpha 1 (I) chain was cleaved in native or denatured collagen only within the carboxy-terminal extra-helical sequence, the major site being between resides C6 (Leu) and C7 (Ser). The alpha 2 chain was unaffected in native collagen but was slowly cleaved between residues 782 (Phe) and 783 (Leu) in the denatured form. Cleavages, at 45 degrees C, in type III collagen occur within the extra-helical amino-terminal sequence, on the carboxy-terminal side of the lysine residue involved in intermolecular cross-linking. All three sites of action are within sequences of general hydrophobic character. 2. The very restricted cleavage of peptide bonds in denatured collagens can be ascribed to the infrequent occurrence of groupings of more than two hydrophobic residues and to the high content of the conformation-limiting residues proline and hydroxyproline. 3. The previously demonstrated failure of cathepsin D to solubilize a representative proportion of type III collagen from the fibres of bovine skin collagen [P.G. Scott and C.H. Pearson (1978) Biochem, Soc, Trans. 6, 1197-1199] may be explained by lack of ability of the enzyme to act on this collagen at 25 degrees C, in such a manner as to separate molecules joined by intermolecular cross-links involving the amino-terminal extrahelical region of the molecule.

Prolyl 3-Hydroxylase 1, Enzyme Characterization and Identification of a Novel Family of Enzymes

The collagen prolyl hydroxylases are enzymes that are required for proper collagen biosynthesis, folding, and assembly. They reside within the endoplasmic reticulum and belong to the group of 2-oxoglutarate and iron-dependent dioxygenases. Although prolyl 4-hydroxylase has been characterized as an alpha2beta2 tetramer in which protein disulfide isomerase is the beta subunit with two different alpha subunit isoforms, little is known about the enzyme prolyl 3-hydroxylase (P3H). It was initially characterized and shown to have an enzymatic activity distinct from that of prolyl 4-hydroxylase, but no amino acid sequences or genes were ever reported for the mammalian enzyme. Here we report the characterization of a novel prolyl 3-hydroxylase enzyme isolated from embryonic chicks. The primary structure of the enzyme, which we now call P3H1, demonstrates that P3H1 is a member of a family of prolyl 3-hydroxylases, which share the conserved residues present in the active site of prolyl 4-hydroxylase and lysyl hydroxylase. P3H1 is the chick homologue of mammalian leprecan or growth suppressor 1. Two other P3H family members are the genes previously called MLAT4 and GRCB. In this study we demonstrate prolyl 3-hydroxylase activity of the purified enzyme P3H1 on a full-length procollagen substrate. We also show it to specifically interact with denatured collagen and to exist in a tight complex with other endoplasmic reticulum-resident proteins. Immunohistochemistry with a monoclonal antibody specific for chick P3H1 localizes P3H1 specifically to tissues that express fibrillar collagens, suggesting that other P3H family members may be responsible for modifying basement membrane collagens.

Hierarchical assembly and the onset of banding in fibrous long spacing collagen revealed by atomic force microscopy

The mechanism of formation of fibrillar collagen with a banding periodicity much greater than the 67 nm of native collagen, i.e. the so-called fibrous long spacing (FLS) collagen, has been speculated upon, but has not been previously studied experimentally from a detailed structural perspective. In vitro, such fibrils, with banding periodicity of approximately 270 nm, may be produced by dialysis of an acidic solution of type I collagen and alpha(1)-acid glycoprotein against deionized water. FLS collagen assembly was investigated by visualization of assembly intermediates that were formed during the course of dialysis using atomic force microscopy. Below pH 4, thin, curly nonbanded fibrils were formed. When the dialysis solution reached approximately pH 4, thin, filamentous structures that showed protrusions spaced at approximately 270 nm were seen. As the pH increased, these protofibrils appeared to associate loosely into larger fibrils with clear approximately 270 nm banding which increased in diameter and compactness, such that by approximately pH 4.6, mature FLS collagen fibrils begin to be observed with increasing frequency. These results suggest that there are aspects of a stepwise process in the formation of FLS collagen, and that the banding pattern arises quite early and very specifically in this process. It is proposed that typical 4D-period staggered microfibril subunits assemble laterally with minimal stagger between adjacent fibrils. alpha(1)-Acid glycoprotein presumably promotes this otherwise abnormal lateral assembly over native-type self-assembly. Cocoon-like fibrils, which are hundreds of nanometers in diameter and 10-20 microm in length, were found to coexist with mature FLS fibrils.

Impaired balance of type I and type III procollagen mRNA in cultured fibroblasts of patients with incisional hernia

BACKGROUND

Recent findings of an impaired protein ratio of type I to type III procollagen showed a disturbed collagen metabolism in incisional hernia development. We analyzed the type I and type III procollagen messenger RNA to investigate whether these findings represent the altered extracellular matrix or a primary defect at the transcriptional level.

METHODS

We examined cultured skin fibroblasts of patients with incisional or recurrent incisional hernia in comparison with those without any previous incision (control) and those with a skin scar without clinical appearance of a hernia (scar). Immunohistochemical detection of a lowered protein ratio of type I and type III collagen in the hernia skin tissue leads to mRNA expression analysis. The procollagen mRNA and the ratio of type I to type III procollagen mRNA are detected by reverse transcriptase-polymerase chain reaction and Northern blot analysis, the collagens type I and III by Western blot analysis.

RESULTS

Reverse transcriptase-polymerase chain reaction revealed an increase of type I procollagen mRNA in the incisional and recurrent hernia (0.90 +/- 0.04 and 1.19 +/- 0.04, respectively) compared with stable scar (0.54 +/- 0.02) or healthy tissue (0.43 +/- 0.01). The obvious rise of type III procollagen mRNA to 4.13 +/- 0.04 for incisional, 6.02 +/- 0.03 for recurrent hernia, 2.29 +/- 0.04 for stable scar, and 1.72 +/- 0.03 for the healthy tissue showed a significantly decreased ratio of type I to type III procollagen mRNA in the hernia patients as compared with the controls (P <.01). By Western blot analysis, an increase of type I and type III collagen protein and a significant rise in the corresponding ratio in the recurrent hernia group were detected.

CONCLUSIONS

The altered synthesis of type I and type III collagen in cultured skin fibroblasts suggests a disorder of collagen metabolism, at least in patients with recurrent hernia. Hence, a basically impaired wound healing process is likely to contribute to the unsatisfactory results of incisional hernia repair.

Effects of singlet oxygen on the extracellular matrix protein collagen: oxidation of the collagen crosslink histidinohydroxylysinonorleucine and histidine

The reaction of singlet oxygen, a putative agent of skin photodamage, with the dermal collagen crosslink histidinohydroxylysinonorleucine (HHL) and its precursor histidine is reported. Reaction studies were performed with both purified HHL and bovine dermal tissue. We demonstrate that singlet oxygen can selectively oxidize HHL and histidine amino acid residues in dermal tissue and that intermediate oxidation products of histidine lead to new crosslink products. A novel mechanism for crosslink formation was proposed to involve nucleophilic addition to a transient imidazolone intermediate formed from singlet oxygen oxidation of the histidine imidazole moiety. The implication for such adduct formation and histidine oxidation in collagen proteins is the expression of aberrant collagen crosslinks, perturbation of the dermal collagen function, and hence an altered dermal state.

Stability of collagen during denaturation

The stability of calf skin collagen (CSC) type I during thermal and chemical denaturation in the presence of glycerol was investigated. Thermal denaturation of type I collagen was performed in the presence of glycerol or in combination with urea and sodium chloride. The denaturation curves obtained in the presence of urea or sodium chloride retained their original shape without glycerol. These curves were shifted upward proportionally to the glycerol concentration in the reaction medium. This means that glycerol and the denaturants act independently. The explanation is based on the difference in the mechanism of their action on the collagen molecule.

Fibronectin-binding peptides. I. Isolation and characterization of two unique fibronectin-binding peptides from gelatin

Gelatin binds to fibronectin with a high affinity although the fibronectin-binding components have not been located. Fibronectin plays an important role in tumor cell metastasis and gelatin may have a profound effect on the metastatic process. In this study, fractionated acid-washed gelatin was cleaved with trypsin and resultant peptides fractionated by fibronectin-Sepharose affinity chromatography. After further purification using size exclusion HPLC and then reverse-phase HPLC, two unique peptides were obtained and sequenced. The binding affinities of these two peptides to fibronectin were evaluated by an ELISA method developed during this study and compared with the gelatin. Both possessed significantly higher binding affinities to fibronectin than gelatin alone.

Collagens in the liver extracellular matrix bind hepatocyte growth factor

BACKGROUND & AIMS

Hepatocyte growth factor (HGF), a potent mitogen for hepatocytes, binds to heparan sulfate. Because immunoreactive HGF can be detected in the interstitial extracellular matrix (ECM), where little heparan sulfate is found, the aim of this study was to investigate binding of HGF to several collagens and noncollagenous ECM proteins in vitro.

METHODS

125I-labeled HGF was incubated with collagens I-VI, single collagen chains and their cyanogen bromide peptides, with fibronectin, fibrinogen, and laminin that were either immobilized on polystyrene or blotted to nitrocellulose after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Biological activity of collagen-bound HGF was investigated in cell culture.

RESULTS

HGF displayed binding of moderate affinity (Kd approximately 10(-9) mol/L) to immobilized collagen types I, III, IV, V, and VI. Binding of HGF to all collagens could be inhibited by single chains of either collagens I, III, or VI. Fragmentation with cyanogen bromide indicated unique collagenous peptides mediating the interaction. Collagen-bound HGF induced primary hepatocyte proliferation and MDCK cell scattering in a dose-dependent manner.

CONCLUSIONS

Interstitial collagens I, III, V, and VI serve as abundant, low-affinity binding sites for HGF in the ECM. This interaction is mediated by unique collagenous peptides, opening the potential to modulate HGF availability and activity by collagen-derived peptide analogues.

Post-translational non-enzymatic modification of proteins. II. Separation of selected protein species after glycation and other carbonyl-mediated modifications

There are two strategies applicable to revealing non-enzymatic post-translational modifications of proteins; while assaying of the hydrolytically stable adducts was the subject of our previous communication [1], here we attempted to review separation technologies for the unfragmented modified proteins. There are a few standard procedures used for this purpose, namely Laemmli gel electrophoresis, different modes of gel permeation chromatography and boronate affinity chromatography. The latter approach makes use of the vicinal hydroxy groups present in glycated proteins. Some (but not all) arising adducts exhibit typical fluorescence which can be exploited for detection. In most cases fluorescence is measured at 370/440 nm for the so-called advanced glycation products or at 335/385 nm for the only so far well characterized glycation marker (pentosidine). Some indication exists that, e.g., synchronous fluorescence detection will probably in the future add to the selectivity and allow the distinction of the different adducts arising during non-enzymatic post-translational modifications (glycation). The proteins reviewed are serum albumin, collagen and lens proteins while glycation of hemoglobin is the subject of another review within the present volume.

Thermal stability of calf skin collagen type I in salt solutions

The thermal stability of acid-soluble collagen type I from calf skin in salt solutions is studied by high-sensitivity differential scanning calorimetry. Three concentration ranges have been clearly distinguished in the dependence of collagen thermal stability on ion concentration. At concentrations below 20 mM, all studied salts reduce the temperature of collagen denaturation with a factor of about 0.2 degree C per 1 mM. This effect is attributed to screening of electrostatic interactions leading to collagen stabilisation. At higher concentrations, roughly in the range 20-500 mM, the different salts either slightly stabilise or further destabilise the collagen molecule in salt-specific way that correlates with their position in the lyotropic series. The effect of anions is dominating and follows the order H2PO4- > or = SO4(2-) > Cl- > SCN-, with sign inversion at about SO4(2-). This effect, generally known as the Hofmeister effect, is associated with indirect protein-salt interactions exerted via competition for water molecules between ions and the protein surface. At still higher salt concentrations (onset concentrations between 200 and 800 mM for the different salts), the temperature of collagen denaturation and solution opacity markedly increase for all studied salts due to protein salting out and aggregation. The ability of salts to salt out collagen also correlates with their position in the lyotropic series and increases for chaotropic ions. The SO4(2-) anions interact specifically with collagen - they induce splitting of the protein denaturation peak into two components in the range 100-150 mM Na2SO4 and 300-750 mM Li2SO4. The variations of the collagen denaturation enthalpy at low and intermediate salt concentrations are consistent with a weak linear increase of the enthalpy with denaturation temperature. Its derivative, d(delta H)/dT, is approximately equal to the independently measured difference in the heat capacities of the denatured and native states, delta Cp = Cp(D) - Cp(N) approximately 0.1 cal.g-1 K-1.

Capillary zone electrophoresis of collagen type I CNBr peptides in acid buffers

Collagen type-I CNBr peptides were separated under acidic conditions by capillary electrophoresis. Separation conditions were: 100 mM phosphate buffer pH 2.5, 50 cm x 50 microns capillary (placed in a cartridge), 8 kV, running time 30-45 min, detection by UV at 200 nm. The peptides were separated strictly by their molecular mass and the overall pattern was well comparable to RP-HPLC separations of these analytes. It is proposed that the separation mechanism may involve hydrophobic sorptions to the capillary wall.

The effect of deamination and/or blocking arginine residues on the molecular assembly of acid-extracted rat tail tendon collagen

We describe the effect of deamination of lysine and blocking of arginine residues on the assembly of collagen into native fibrils and SLS aggregates. Treatment of collagen solutions with one or both of these procedures does not prevent the formation of fibrils or SLS aggregates but reduces their ability to form assemblies with accurate longitudinal registration. These observations provide direct confirmation that hydrophobic interactions are important in collagen assembly. Unbanded fibrils were formed within the first 24 h at 4 degrees C from both acidic and neutralized deaminated and from neutralized control collagen solutions, transversely banded fibrils appearing later. This is compatible with the suggestion that initially, collagen fibrils are assembled by lyotropic liquid crystallization and with other observations which suggest that collagen molecules are initially free to move laterally within the fibril before being locked into place. Fibrils assembled from deaminated collagen solution show two variant longitudinal registration patterns which grade into one another. This suggests that, with a reduction in positively charged side chains, the thermodynamic energy minima responsible for longitudinal registration are less sharp compared with control collagen solutions. Reduction of positive charge by chemical modification helps to explain why the chemical modifications reduce swelling of collagen fibres. It also helps to explain why fibrils form spontaneously at 4 degrees C in both arginine-blocked and deaminated collagen solutions. Thus chemical modifications of rat tail tendon provides new insight into the mechanisms in collagen assembly.

Cloning, expression, and type II collagenolytic activity of matrix metalloproteinase-13 from human osteoarthritic cartilage

Proteolysis of triple-helical collagen is an important step in the progression toward irreversible tissue damage in osteoarthritis. Earlier work on the expression of enzymes in cartilage suggested that collagenase-1 (MMP-1) contributes to the process. Degenerate reverse transcription polymerase chain reaction experiments, Northern blot analysis, and direct immunodetection have now provided evidence that collagenase-3 (MMP-13), an enzyme recently cloned from human breast carcinoma, is expressed by chondrocytes in human osteoarthritic cartilage. Variable levels of MMP-13 and MMP-1 in cartilage was significantly induced at both the message and protein levels by interleukin-1 alpha. Recombinant MMP-13 cleaved type II collagen to give characteristic 3/4 and 1/4 fragments; however, MMP-13 turned over type II collagen at least 10 times faster than MMP-1. Experiments with intact type II collagen as well as a synthetic peptide suggested that MMP-13 cleaved type II collagen at the same bond as MMP-1, but this was then followed by a secondary cleavage that removed three amino acids from the 1/4 fragment amino terminus. The expression of MMP-13 in osteoarthritic cartilage and its activity against type II collagen suggest that the enzyme plays a significant role in cartilage collagen degradation, and must consequently form part of a complex target for proposed therapeutic interventions based on collagenase inhibition.

Unique side-chain conformation encoding for chirality and azimuthal orientation in the molecular packing of skin collagen

We used molecular mechanics to study the role of gly X-Y+ sequences, where X- was Asp or Glu and Y+ was Lys or Arg, in the molecular packing of type I collagen. In the minimal energy conformation of a triply stranded molecule having a coiled-coil configuration, the side-chains of these sequences segregated into two oppositely charged groupings of the forms X-Y+X- and Y+X-Y+. Groupings having the same net charge were clustered along two complementary azimuthal edges of the molecule. Intermolecular interactions, through these oppositely charged edges, align the molecules appropriately for the formation of the HHL crosslink of skin. This alignment also can account for the axial periodicity and chiral appearance of skin collagen fibrils.