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PubMed1993

Emilin, a component of elastic fibers preferentially located at the elastin-microfibrils interface.

The fine distribution of the extracellular matrix glycoprotein emilin (previously known as glycoprotein gp115) (Bressan, G. M., I. Castellani, A. Colombatti, and D. Volpin. 1983. J. Biol. Chem. 258: 13262-13267) has been studied at the ultrastructural level with specific antibodies. In newborn chick aorta the protein was exclusively found within elastic fibers. In both post- and pre-embedding immunolabeling emilin was mainly associated with regions where elastin and microfibrils are in close contact, such as the periphery of the fibers. This localization of emilin in aorta has been confirmed by quantitative evaluation of the distribution of gold particles within elastic fibers. In other tissues, besides being associated with typical elastic fibers, staining for emilin was found in structures lacking amorphous elastin, but where the presence of tropoelastin has been demonstrated by immunoelectron microscopy. This was particularly evident in the oxitalan fibers of the corneal stroma, in the Descemet's membrane, and in the ciliary zonule. Analysis of embryonic aorta revealed the presence of emilin at early stages of elastogenesis, before the appearance of amorphous elastin. Immunofluorescence studies have shown that emilin produced by chick embryo aorta cells in culture is strictly associated with elastin and that the process of elastin deposition is severely altered by the presence of antiemilin antibodies in the culture medium. The name of the protein was derived from its localization at sites where elastin and microfibrils are in proximity (emilin, elastin microfibril interface located protein).

Animals↗
PubMed1975

Production of cellulose microfibrils by Rhizobium.

Electron microscope examination of Rhizobium spp. revealed microfibrils produced by flocculating strains but not by nonflocculating strains. The microfibrils from R. trifolii (NA30) were isolated and identified as cellulose by enzymatic, X-ray diffraction, and infrared spectral analyses. Both infective and noninfective strains of R. trifolii flocculated and produced microfibrils. More infection threads were observed in clover root hairs growing in the presence of flocs in comparison with root hairs where single bacterial cells predominated.

Cell Adhesion↗
PubMed1999

Ultrastructural distribution of 36-kD microfibril-associated glycoprotein (MAGP-36) in human and bovine tissues.

We observed the ultrastructural distribution of MAGP-36 by immunoelectron microscopy in human and bovine tissues. MAGP-36 was present in microfibrils associated with tropoelastin in skin, aorta, and spleen. It was not detected in microfibrils from the ocular zonule and kidney mesangium that were not associated with tropoelastin. In skin, MAGP-36 was present in both early immature elastic fibers and mature elastic fibers. In mature elastic fibers, MAGP-36 was localized around amorphous elastic cores at the elastin-microfibril interface and in electron-dense bundles. Localization of MAGP-36 in elastic fibers coincided with the distribution of lysyl oxidase, an enzyme that plays a pivotal role in the deposition of tropoelastin. These findings suggest that MAGP-36 may be involved in elastogenesis.

Animals↗
PubMed1982

Histochemical and ultrastructural characterization of subendothelial glycoprotein microfibrils interacting with platelets.

The interaction of human blood platelets with collagenase-treated rabbit subendothelium was studied by histochemical ultrastructural methods and by morphometric semi-quantitative analysis. Aortas were deendothelialized and incubated: 1) with a highly purified bacterial collagenase whose specificity was controlled; and 2) with the same collagenase followed by chymotrypsin. For histochemical studies, tannic acid, ruthenium red, and peroxidase-labeled Ricinus communis and concanavalin A were used. Electron microscopy showed that after digestion of fibrillar collagen by collagenase, adherent and aggregated platelets were observed on Ricinus communis-, concanavalin A-, and ruthenium red-positive glycoprotein microfibrils. After successive incubation with collagenase and chymotrypsin, the microfibrils disappeared. No platelets were observed on the remnant amorphous elastin. Morphometric analysis confirmed the interaction of platelets with collagenase-treated subendothelium. In addition, glycoproteins were extracted from collagenase-treated rabbit aortas using 5 M guanidine. Using an in vitro quantitative test, significant platelet adhesion to these glycoproteins was observed. Our results show an interaction between platelets and noncollagenic glycoprotein microfibrils.

Animals↗
PubMed1991

Thrombospondin: a component of microfibrils in various tissues.

We used antisera directed against human platelet thrombospondin (TSP) and microfibril-associated GP 128 to localize the presence of these glycoproteins in fixed sections of human placenta or porcine arteries and skin by immunogold labeling, using electron microscopy. These two antibodies reacted with both human and porcine tissues and always recognized the same structures. In all three tissues the antibodies were associated with the basement membranes and, more precisely, with the microfibrillar structures present at the junction between the basement membrane and the adjacent connective tissue. This localization indicates that GP 128 and TSP are associated with the microfibrils, and suggests their possible role in the attachment of basement membrane to the connective tissue meshwork. Their presence in microfibrils associated with the subendothelial basement membrane in arteries may be important in regard to the thrombogenicity of the subendothelium since, after an endothelial lesion, they may be directly accessible to blood platelets.

Actin Cytoskeleton↗
PubMed1986

Cellulose microfibril orientation in Oocystis solitaria: proof that microtubules control the alignment of the terminal complexes.

In the green alga Oocystis solitaria microtubules control the regular deposition of cellulose microfibrils. Although it has frequently been suggested that the influence of the cortical microtubules is mediated through the alignment of structures in the plasma membrane, e.g. the cellulose-synthesizing enzymes, experimental proof is lacking. In Oocystis the putative cellulose-synthesizing units, the so-called terminal complexes, can be visualized following freeze-fracture. With respect to the synthesis of a given layer of microfibrils two distinct situations are observable: terminal complex doublets occur before the start of cellulose formation, but are subsequently separated into single terminal complexes by pressure exerted by the crystallizing microfibrils. In order to investigate the effect of anti-microtubular substances on the orientation of the terminal complexes, the state of cellulose deposition at the time of drug application was marked by short (15-30 min) treatment with Congo Red, which causes a morphological change in the terminal complexes. The characteristic alignment of the terminal complexes, both doublets and fragmented single ones, is severely disturbed in cells treated with the herbicide amiprophosmethyl, which is known to interfere with the action of microtubules. The results provide strong evidence that microtubules control the alignment of the putative cellulose-forming units in Oocystis. The observed pattern of interference indicates that the microtubules most probably achieve their control by imposing fluidity channels on the membrane and not via direct links with the terminal complexes.

Cell Membrane↗
PubMed1991

The alpha 1 chain of type VIII collagen is associated with many but not all microfibrils of elastic fiber system.

The antigen of monoclonal antibodies which had labeled the hexagonal lattice of Descemet's membrane in a specific manner was shown to be the alpha 1 chain of type VIII collagen by immunoblotting followed by amino acid sequence analysis. With this antibody, the localization of alpha 1 (VIII) in various tissues was studied by several immunocytochemical methods. Under light microscopy, the alpha 1 (VIII) was found in a fine fibrillar form in various capsular tissues such as capsules of the liver, kidneys, adrenals, lungs and so on. It was also present in dense connective tissues such as the Achilles tendon, and periodontal and perivertebral ligaments. When some dense connective tissues which had been negative to the label including the intima of aorta, perimysium and Glisson's sheath of the liver, were subjected to pepsin digestion, epitopes were revealed which showed a specific immunofluorescence pattern. In many locations the pattern of localization coincided with that of elastic fiber components, and full or partial colocalization with tropoelastin or costaining with resorcin-fuchsin staining was observed. In immunoelectron microscopy, the antigen (alpha 1 (VIII)) was localized on the surface of, but not inside, elastic fibers. However, some tissues which are rich in elastic fibers or microfibrils remained unlabeled. These included elastic fibers of the aortic media and ligamentum nuchae as well as ciliary zonules. Therefore it is suggested that alpha 1 (VIII) is a collagen associated with microfibrils of some elastic fiber systems, but is not an intrinsic component of either elastic fibers or of microfibrils.

Amino Acid Sequence↗
PubMed1975

Ultrastructural studies of human gingiva. V. Microfibrils of elastic nature and their direct penetration of the basal lamina in chronic periodontitis.

In this study, microfibrils widely distributed in the connective tissue of the gingival wall of periodontal pockets were examined by electron microscopy, Theirdistribution, ultrastructural characteristics, close association with fibroblasts and direct communication with the basal lamina were shown. The microfibrils in our specimens were observed in three different groupings (Types A, B, and C). They were believedto represent different stages of maturation of elastic fibera. There was a striking ultrastructural resemblance between oxytalan microfibrils, and the immature or imcompletetype of elastic fiber shown in this report.

Basement Membrane↗
PubMed1989

Isolation and characterization of a new 36-kDa microfibril-associated glycoprotein from porcine aorta.

A new connective tissue protein of 36 kDa has been purified from porcine aorta. The biochemical and immunological properties of the protein are distinct from those of microfibril-associated proteins reported previously such as lysyl oxidase, 31-kDa microfibril-associated glycoprotein, and fibrillin. It could bind to concanavalin A-Sepharose and gelatin-Sepharose. The protein contained the sequence Arg-Gly-Asp-Ala in the amino-terminal region, which is the site for the association with cell and extracellular matrix. Using specific antibody raised to the protein, we demonstrated its restricted localization in aorta adventitia. Immunoelectron microscopy specified its location to a class of extracellular structural elements described as elastin-microfibrils.

Amino Acid Sequence↗
PubMed1987

An electron microscopic study of microfibrils of bone marrow.

After fixation of bone marrow with glutaraldehyde, tannic acid and saponin, a delicate network of microfibrils (10 nm) was observed in the extracellular space. Masses of microfibrils were most frequently observed between the endothelial cells of the sinusoidal wall and adventitial reticular cells, but were also observed at other sites throughout the marrow stroma. Microfibrils are an important component of the extracellular material of bone marrow and appear to provide an anchoring substrate for the endothelium.

Animals↗
PubMed1984

Tubular microfibrils in the glomeruli of membranous nephropathy.

The presence of tubular microfibrils in the mesangium and capillary walls of the renal glomeruli is a rare occurrence that has been reported by others in different glomerular disease processes. The two cases presented in this report demonstrated such microfibrils in membranous glomerulonephropathy, an association previously described in only one other case. These microfibrils differed in size and structural characteristics from collagen fibers, amyloid fibrils, and cryoglobulin microtubules.

Adult↗
PubMed2004

Mutant fibrillin 1 from tight skin mice increases extracellular matrix incorporation of microfibril-associated glycoprotein 2 and type I collagen.

OBJECTIVE: Skin fibrosis in the TSK mouse, a model of skin fibrosis seen in systemic sclerosis (SSc), is caused by a large in-frame duplication in the Fbn1 gene, tsk-Fbn1. We investigated whether tsk-Fbn1 might cause dermal fibrosis by affecting Fbn1 and associated extracellular matrices. We also studied whether deposition of microfibril-associated glycoprotein 2 (MAGP-2), a protein that is associated with fibrillin 1, was altered in the skin of patients with SSc. METHODS: An in vitro model of the TSK mouse was created by conditionally expressing tsk-Fbn1 in mouse embryonic fibroblasts (MEFs). Cell cultures were examined by immunofluorescence and Western and Northern blotting to determine the effect of tsk-Fbn1 on the structure, expression, and deposition of fibrillin 1 (Fbn-1), type I collagen, and MAGP-2. The skin of TSK mice and SSc patients was analyzed by immunohistochemistry for MAGP-2 expression. RESULTS: Expression of tsk-Fbn1 in cultured MEF cells altered the morphology of Fbn-1 fibers and increased the deposition of type I collagen into the extracellular matrix (ECM) without concomitantly changing messenger RNA expression, secretion, or processing of type I procollagen. Moreover, MEF cells expressing tsk-Fbn1 showed increased MAGP-2 matrix. MAGP-2 was increased in the dermis of TSK mice. Fibrotic SSc skin also showed higher levels of MAGP-2 in the dermis than nonfibrotic SSc skin and normal skin. CONCLUSION: Tsk-Fbn1 altered ECM organization and caused fibrosis by affecting the deposition of MAGP-2 or other Fbn-1-associated proteins. Alterations in microfibril structure or deposition might contribute to fibrosis in SSc.

Animals↗
PubMed2005

Increased expression of type I collagen induced by microfibril-associated glycoprotein 2: novel mechanistic insights into the molecular basis of dermal fibrosis in scleroderma.

OBJECTIVE: Mutations in fibrillin 1, a key component of extracellular microfibrils, are associated with connective tissue disorders such as Marfan's syndrome or skin fibrosis in the tight skin mouse model of scleroderma. Previous studies have suggested that fibrillin 1 mediates skin fibrosis via its interface with associated microfibrillar proteins and type I collagen; in particular, microfibril-associated glycoprotein 2 (MAGP-2), an extracellular matrix protein that binds to fibrillins and the alphavbeta3 integrin, is increased in TSK mouse and human scleroderma skin. Because the function of MAGP-2 in the biologic processes of the matrix remains unknown, this study investigated whether MAGP-2 regulates type I collagen. METHODS: Fibroblast cultures conditionally overexpressing MAGP-2 were developed. Cells were analyzed by Western blotting, Northern blotting, pulse-chase analysis, and immunofluorescence to assess the effect of MAGP-2 on type I collagen. RESULTS: Cells overexpressing MAGP-2 formed increased MAGP-2 matrix and showed a 3-fold increase in intracellular type I procollagen. This increase was associated with increased levels of type I collagen in the medium and matrix. Increased type I collagen colocalized with the MAGP-2 matrix. MAGP-2 overexpression had no effect on type I procollagen messenger RNA, but markedly increased the half-life of type I procollagen. MAGP-2 induced type I collagen even under conditions in which no MAGP-2 matrix was detectable, and did not require the presence of the RGD motif of MAGP-2 in its integrin-binding site. CONCLUSION: This study shows that MAGP-2 stabilizes type I procollagen, identifying an important function of MAGP-2 in extracellular matrix homeostasis. It also suggests that MAGP-2 might mediate skin fibrosis in TSK mice and in patients with scleroderma.

Animals↗
PubMed2007

Surface functional group dependent apatite formation on bacterial cellulose microfibrils network in a simulated body fluid.

The apatite forming ability of biopolymer bacterial cellulose (BC) has been investigated by soaking different BC specimens in a simulated body fluid (1.5 SBF) under physiological conditions, at 37 degrees C and pH 7.4, mimicking the natural process of apatite formation. From ATR-FTIR spectra and ICP-AES analysis, the crystalline phase nucleated on the BC microfibrils surface was calcium deficient carbonated apatite through initial formation of octacalcium phosphate (OCP) or OCP like calcium phosphate phase regardless of the substrates. Morphology of the deposits from SEM, FE-SEM, and TEM observations revealed the fine structure of thin film plates uniting together to form apatite globules of various size (from <1 mum to 3 mum) with respect to the substrates. Surface modification by TEMPO (2,2,6,6-tetramethylpyperidine-1-oxyl)-mediated oxidation, which can readily form active carboxyl functional groups upon selective oxidation of primary hydroxyl groups on the surface of BC microfibrils, enhanced the rate of apatite nucleation. Ion exchanged treatment with calcium chloride solution after TEMPO-mediated oxidation was found to be remarkably different from other BC substrates with the highest deposit weight and the smallest apatite globules size. The role of BC substrates to induce mineralization rate differs according to the nature of the BC substrates, which strongly influences the growth behavior of the apatite crystals.

Acetobacter↗
PubMed1983

The structure of the alpha-keratin microfibril.

Quantitative measurements of the intensity of the meridional reflections in the X-ray-diffraction pattern of alpha-keratin are shown to be consistent with a microfibril structure in which a surface lattice with an axially projected period around 200 A is subject to a periodic interruption with an axially projected period of 470 A. Taken in conjunction with recent evidence on the chemical structure of alpha-keratin and other intermediate filaments this finding enables an elaboration to be made of a model proposed earlier by RDB Fraser, TP MacRae, & E Suzuki (J. Mol. Biol. 108, 435-452, 1976) for the alpha-helical framework of the microfibril. The disposition and connectivity of the helical segments suggested here provides a straightforward explanation of a number of recent physicochemical and electron-microscopical observations on intermediate filaments and provides a starting point for the development of models for the framework of other intermediate filaments.

Keratins↗
PubMed2004

Structure of the integrin binding fragment from fibrillin-1 gives new insights into microfibril organization.

Human fibrillin-1, the major structural protein of extracellular matrix (ECM) 10-12 nm microfibrils, is dominated by 43 calcium binding epidermal growth factor-like (cbEGF) and 7 transforming growth factor beta binding protein-like (TB) domains. Crystal structures reveal the integrin binding cbEGF22-TB4-cbEGF23 fragment of human fibrillin-1 to be a Ca(2+)-rigidified tetragonal pyramid. We suggest that other cbEGF-TB pairs within the fibrillins may adopt a similar orientation to cbEGF22-TB4. In addition, we have located a flexible RGD integrin binding loop within TB4. Modeling, cell attachment and spreading assays, immunocytochemistry, and surface plasmon resonance indicate that cbEGF22 bound to TB4 is a requirement for integrin activation and provide insight into the molecular basis of the fibrillin-1 interaction with alphaVbeta3. In light of our data, we propose a novel model for the assembly of the fibrillin microfibril and a mechanism to explain its extensibility.

Crystallography, X-Ray↗
PubMed2003

Solid-state 13C and 1H spin diffusion NMR analyses of the microfibril structure for bacterial cellulose.

To obtain further information about the cause for the rather large splitting of the C4 resonance line into the downfield (C4D) and upfield (C4U) lines in CP/MAS 13C NMR spectra for native cellulose, 13C and 1H spin diffusion measurements have been conducted by using different types of bacterial cellulose samples. In 13C spin diffusion measurements, the C4D resonance line is selectively inverted by the Dante pi pulse sequence and the 13C spin diffusion is allowed to proceed from the C4D carbons to other carbons including the C4U carbons with use of the 13C4-enriched bacterial cellulose sample. The analysis based on the simple spin diffusion theory for the process experimentally observed reveals that the C4U carbons may be located at distances less than about 1 nm from the C4D carbons. In 1H spin diffusion measurements, poly(vinyl alcohol) (PVA) films in which ribbon assemblies of bacterial cellulose are dispersed are employed and the 1H spin diffusion process is examined from the water-swollen PVA continuous phase to the dispersed ribbon assemblies by the 13C detection through the 1H-13C CP technique. As a result, it is found that the C4D and C4U carbons are almost equally subjected to the 1H spin diffusion from the PVA phase, indicating that the C4U carbons are not localized in some limited area, e.g. in the surfacial region, but are distributed in the whole area in the microfibrils. These experimental results suggest that the C4U carbons may exist as structural defects probably due to conformational irregularity associated with disordered hydrogen bonding of the CH(2)OH groups in the microfibrils.

Acetobacter↗
PubMedDate not supplied

Fluorescent cellulose microfibrils as substrate for the detection of cellulase activity.

To devise a sensitive cellulase assay based on substrates having most of the physical characteristics of native cellulose, 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF) was used as a grafting agent to prepare suspensions of fluorescent microfibrils from bacterial cellulose. These suspensions were digested by a series of commercially relevant cellulases from Humicola insolens origin: cloned Cel6B and Cel 45A as well as crude H. insolens complex. The digestion induced the release of fluorescent cellodextrins as well as reducing sugars. After adequate centrifugation, these soluble products were analyzed as a function of grafting content, digestion time, and cellulase characteristics. The resulting data allowed the grafting conditions to be optimized in order to maximize the quantity of soluble products and therefore to increase the sensitivity of the detection. A comparison between the amount of released fluorescence and that of released reducing sugar allowed the differentiation between processive exo and endo cellulase activities. The casting of films of DTAF-grafted microfibrils at the bottom of the microwell titer plates also led to sensitive cellulase detection. As these films kept their integrity and remained firmly glued to the well bottom during the digestion time, they are tailored made for a full automation of the cellulases testing.

Cellulase↗