The Evolution of Extracellular Fibrillins and Their Functional Domains

Fibrillins constitute the major backbone of multifunctional microfibrils in elastic and non-elastic extracellular matrices, and are known to interact with several binding partners including tropoelastin and integrins. Here, we study the evolution of fibrillin proteins. Following sequence collection from 39 organisms representative of the major evolutionary groups, molecular evolutionary genetics and phylogeny inference software were used to generate a series of evolutionary trees using distance-based and maximum likelihood methods. The resulting trees support the concept of gene duplication as a means of generating the three vertebrate fibrillins. Beginning with a single fibrillin sequence found in invertebrates and jawless fish, a gene duplication event, which coincides with the appearance of elastin, led to the creation of two genes. One of the genes significantly evolved to become the gene for present-day fibrillin-1, while the other underwent evolutionary changes, including a second duplication, to produce present-day fibrillin-2 and fibrillin-3. Detailed analysis of several sequences and domains within the fibrillins reveals distinct similarities and differences across various species. The RGD integrin-binding site in TB4 of all fibrillins is conserved in cephalochordates and vertebrates, while the integrin-binding site within cbEGF18 of fibrillin-3 is a recent evolutionary change. The proline-rich domain in fibrillin-1, glycine-rich domain in fibrillin-2 and proline-/glycine-rich domain in fibrillin-3 are found in all analyzed tetrapod species, whereas it is completely replaced with an EGF-like domain in cnidarians, arthropods, molluscs and urochordates. All collected sequences contain the first 9-cysteine hybrid domain, and the second 8-cysteine hybrid domain with exception of arthropods containing an atypical 10-cysteine hybrid domain 2. Furin cleavage sites within the N- and C-terminal unique domains were found for all analyzed fibrillin sequences, indicating an essential role for processing of the fibrillin pro-proteins. The four cysteines in the unique N-terminus and the two cysteines in the unique C-terminus are also highly conserved

Increased classical endoplasmic reticulum stress is sufficient to reduce chondrocyte proliferation rate in the growth plate and decrease bone growth

Copyright: © 2015 Kung et al. Mutations in genes encoding cartilage oligomeric matrix protein and matrilin-3 cause a spectrum of chondrodysplasias called multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). The majority of these diseases feature classical endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) as a result of misfolding of the mutant protein. However, the importance and the pathological contribution of ER stress in the disease pathogenesis are unknown. The aim of this study was to investigate the generic role of ER stress and the UPR in the pathogenesis of these diseases. A transgenic mouse line (ColIITgcog) was generated using the collagen II promoter to drive expression of an ER stress-inducing protein (Tgcog) in chondrocytes. The skeletal and histological phenotypes of these ColIITgcog mice were characterised. The expression and intracellular retention of Tgcog induced ER stress and activated the UPR as characterised by increased BiP expression, phosphorylation of eIF2á and spliced Xbp1. ColIITgcog mice exhibited decreased long bone growth and decreased chondrocyte proliferation rate. However, there was no disruption of chondrocyte morphology or growth plate architecture and perturbations in apoptosis were not apparent. Our data demonstrate that the targeted induction of ER stress in chondrocytes was sufficient to reduce the rate of bone growth, a key clinical feature associated with MED and PSACH, in the absence of any growth plate dysplasia. This study establishes that classical ER stress is a pathogenic factor that contributes to the disease mechanism of MED and PSACH. However, not all the pathological features of MED and PSACH were recapitulated, suggesting that a combination of intra- and extra-cellular factors are likely to be responsible for the disease pathology as a whole

New live screening of plant-nematode interactions in the rhizosphere

Abstract Free living nematodes (FLN) are microscopic worms found in all soils. While many FLN species are beneficial to crops, some species cause significant damage by feeding on roots and vectoring viruses. With the planned legislative removal of traditionally used chemical treatments, identification of new ways to manage FLN populations has become a high priority. For this, more powerful screening systems are required to rapidly assess threats to crops and identify treatments efficiently. Here, we have developed new live assays for testing nematode responses to treatment by combining transparent soil microcosms, a new light sheet imaging technique termed Biospeckle Selective Plane Illumination Microscopy (BSPIM) for fast nematode detection, and Confocal Laser Scanning Microscopy for high resolution imaging. We show that BSPIM increased signal to noise ratios by up to 60 fold and allowed the automatic detection of FLN in transparent soil samples of 1.5 mL. Growing plant root systems were rapidly scanned for nematode abundance and activity, and FLN feeding behaviour and responses to chemical compounds observed in soil-like conditions. This approach could be used for direct monitoring of FLN activity either to develop new compounds that target economically damaging herbivorous nematodes or ensuring that beneficial species are not negatively impacted

Fibrillin-1, a calcium binding protein of extracellular matrix.

Fibrillin-1 is a large extracellular matrix glycoprotein which assembles to form 10-12 nm microfibrils in extracellular matrix. Mutations in the human fibrillin-1 gene (FBN-1) cause the connective tissue disease Marfan syndrome and related disorders, which are characterised by defects in the skeletal, cardiovascular and ocular systems of the body. Fibrillin-1 has a striking modular organisation which is dominated by multiple tandem repeats of the calcium binding epidermal growth factor-like (cbEGF) domain. This review focuses on recent studies which have investigated the structural and functional role of calcium binding to cbEGF domains in fibrillin-1 and 10-12 nm microfibrils

Defective secretion of recombinant fragments of fibrillin-1: implications of protein misfolding for the pathogenesis of Marfan syndrome and related disorders.

Fibrillin-1 is a large modular glycoprotein that assembles to form 10-12 nm microfibrils in the extracellular matrix. Mutations in the fibrillin-1 gene (FBN1) cause Marfan syndrome and related connective tissue disorders (fibrillinopathies) that show autosomal dominant inheritance. The pathogenic mechanism is thought to be a dominant negative effect of a mutant protein on microfibril assembly, although direct evidence is lacking. A significant group of disease-causing FBN1 mutations are cysteine substitutions within EGF domains that are predicted to cause misfolding by removal of disulphide bonds that stabilize the native domain fold. We have studied three missense mutations (C1117Y, C1129Y and G1127S) to investigate the effect of misfolding on the trafficking of fibrillin-1 from fibroblast cells. We demonstrate that both C1117Y and C1129Y, expressed as recombinant fragments of fibrillin-1, are retained and accumulate within the cell. Both undergo core glycosylation but lack the complex glycosylation observed in the secreted wild-type fragment, suggesting retention in the endoplasmic reticulum (ER). In addition, co-immunoprecipitation experiments show association with the ER chaperone calreticulin, but not calnexin, 78 kDa glucose-regulated protein (Grp78/BiP) or protein disulfide isomerase. In contrast, G1127S, which causes a moderate change in the EGF domain fold, shows a pattern of glycosylation and trafficking profile indistinguishable from the wild-type fragment. Since expression of the recombinant fragments does not disrupt the secretion of endogenous fibrillin-1 by the cell, we propose that G1127S causes disease via an extracellular dominant negative effect. In contrast, the observed ER retention of C1117Y and C1129Y suggests that disease associated with these missense mutations is caused either by an intracellular dominant negative effect or haploinsufficiency

Fibrillin-1 misfolding and disease.

Fibrillin-1 is a 350 kDa calcium-binding protein which assembles to form 10-12 nm microfibrils in the extracellular matrix (ECM). The structure of fibrillin-1 is dominated by two types of disulfide-rich motifs, the calcium- binding epidermal growth factor-like (cbEGF) and transforming growth factor beta binding protein-like (TB) domains. Disruption of fibrillin-1 domain structure and function contributes to the pathogenic mechanisms underlying two inherited diseases with very different etiologies: Marfan syndrome (MFS) and homocystinuria (HC). MFS is a connective tissue disease caused by mutations in the fibrillin-1 gene FBN1. Many missense mutations cause variable degrees of fibrillin-1 domain misfolding, which may affect the delivery of fibrillin-1 to the ECM and/or its assembly into microfibrils. HC is a metabolic disorder which affects methionine metabolism and results in raised serum levels of the highly reactive thiol-containing amino acid homocysteine. Patients with HC often exhibit ocular and skeletal defects resembling the MFS phenotype, suggesting that elevated homocysteine levels may lead to chemical reduction of disulfide bonds within fibrillin-1 domains resulting in the loss of native structure. Protein misfolding therefore is implicated in pathogenic mechanisms underlying MFS and HC

(1)H, (13)C and (15)N assignments of EGF domains 4 to 7 of human Notch-1

The Notch pathway is a core cell–cell signaling system in Metazoa which plays a key role in development and adult homeostasis. Whereas most Notch structural biology research has focused on the negative regulatory region and the intracellular domain, relatively little structural information is available for the extracellular part of human Notch-1 (hN-1) which mediates ligand recognition. This region consists of 36 epidermal growth factor-like (EGF) domains, many of which contain a calcium-binding consensus sequence. The calcium-binding site in each case is located within the N-terminal portion of the domain, and is associated with both intra- and inter-domain rigidity. The absence of calcium-binding sites in EGF6, EGF10 and EGF22, however, suggests that these domains might represent regions of flexibility in the receptor which could influence the cell-surface architecture (usually depicted as an extended rod projecting from the cell surface). To probe this, we have purified a quadruple-domain construct from hN-1, in which the non-calcium-binding EGF6 is flanked by EGF4–5 and EGF7. Here, we report 1H, 13C and 15N resonance assignments for this four-domain 157 amino acid construct. The assignments presented here are the prerequisite for a detailed study of the structure and dynamics of this region of the Notch receptor

Marfan syndrome caused by a mutation in FBN1 that gives rise to cryptic splicing and a 33 nucleotide insertion in the coding sequence.

We have studied a patient with Marfan syndrome whose mutation was not detected by heteroduplex analysis. Primary cultured patient fibroblasts were metabolically labelled and found to secrete fibrillin-1 defectively when compared with an age-matched control. Sequencing of patient cDNA, isolated by reverse transcription-polymerase chain reaction of patient fibroblast RNA, detected a 33-bp insertion. The reading frame of the mutant allele was maintained and predicted the insertion of 11 amino acids at the beginning of calcium-binding epidermal growth factor-like domain 29. Direct sequencing of genomic DNA detected a heterozygous G+1-->A transversion in intron 46 of FBN1. The 11 amino acid insertion was the consequence of the usage of a cryptic splice site 33-bp downstream of the mutation. This is the first reported case of a splicing defect in FBN1 leading to the production of a full-length fibrillin-1 transcript containing a large amino acid insertion