Primary structures of bovine elastin a, b, and c deduced from the sequences of cDNA clones

Structure of the elastin gene and alternative splicing of elastin mRNA: implications for human disease

The protein elastin is largely responsible for the elastic properties of vertebrate lungs, large blood vessels, and skin. The structure of the human, bovine, and chick elastin gene and protein monomer, tropoelastin, has recently been elucidated by using techniques of molecular biology. Extensive homology of amino acid sequence exists among the mammalian species and there is in addition strong conservation of nucleotide sequences in the 3' untranslated region of the gene. The translated exons are small and embedded in large expanses of introns. Sequences coding for the hydrophobic regions, responsible for the elastic properties of the molecule, and the alanine-lysine rich regions, responsible for crosslink formation between molecules, reside in separate exons and alternate for the most part in the elastin gene. S1 analyses and sequence analysis of cDNA and genomic clones have indicated that there is substantial alternative splicing of the primary elastin transcript. Variations in the structure of mRNAs resulting from alternative splicing could explain the existence of the multiple forms of tropoelastin observed electrophoretically in several species. Different kinds of splicing patterns could occur in human populations and may contribute to aging and pathological situations in the cardiovascular and pulmonary systems.

Structure of the bovine elastin gene and S1 nuclease analysis of alternative splicing of elastin mRNA in the bovine nuchal ligament

Genomic clones encompassing all the translated sequences, the 3' untranslated sequence, and 1 kb flanking the ATG translation initiation codon of bovine tropoelastin have been obtained and characterized by restriction enzyme analysis and extensive DNA sequencing. These analyses demonstrated that functionally distinct hydrophobic and cross-linking domains of the protein are segregated into separate exons throughout the gene. The putative promoter region lacks a TATA box, has an extremely high G+C content, and contains several SP1 binding sites. Comprehensive S1 analyses using probes covering the entire mRNA and RNA isolated from the nuchal ligament of bovine fetuses of different ages, neonate calves, and adult cows demonstrated that while only a single exon is alternatively spliced at high frequency, many exons are alternatively spliced at limited, variable frequencies. The results also suggest that such limited splicing is increased in the adult tissue relative to fetal and neonate tissues.

Characterization of rat heart tropoelastin

Several overlapping rat tropoelastin cDNA clones were isolated from a lambda gt11 rat heart cDNA library and their nucleotide sequence was determined. The corresponding deduced amino acid sequence of rat tropoelastin revealed strong homology to bovine and human tropoelastins although possessing some unique features including greater size (18%) and composition of repetitive units. Comparison of the amino acid sequence of rat tropoelastin to four other tropoelastin species reveals that the hydrophobic peptide repeat regions in the middle of each molecule and the crosslinking areas containing three lysine residues are remarkably conserved. A possible function for the clustering of three lysine residues in providing a mechanism for the in vivo reduction of dehydrolysinonorleucine via a redox shuttle with dihydrodesmosine is proposed. In addition, the COOH-terminal sequence of the rat tropoelastin is virtually identical to tropoelastins of other species in possessing a cysteine/arginine/lysine containing segment. There are no obvious amino acid insertions or substitutions in the COOH-terminal half of the rat tropoelastin molecule which would signal unique cleavage or glycosylation sites. Examination of the steady-state levels of rat tropoelastin mRNA in 8- and 12-day neonatal lung, heart, and aortic tissues showed that the amount of tropoelastin mRNA was abundant and of similar size (3.9 kb) in all three tissues.

Characterization of elastin protein and mRNA from salmonid fish (Oncorhynchus kisutch)

1. Elastin was isolated from the bulbus arteriosus of a salmonid fish. Monoclonal and polyclonal antibodies, elicited against a CNBr digest of this protein, immunoprecipitated a polypeptide of Mr 43,000 from fish cell culture medium. 2. Cell-free translation of salmon poly A+ RNA produced a protein of approximately 43 kD that was immunoprecipitated with anti-elastin antibodies. The corresponding mRNA had an approximate Mr of 2 kb. 3. Despite similarities in amino acid composition, the differences in Mr between mammalian and salmon mRNA and protein suggest a divergence of fish and higher vertebrate elastins from an earlier ancestral gene.

The glue protein of ribbed mussels (Geukensia demissa): a natural adhesive with some features of collagen

The Atlantic ribbed mussel Geukensia (Modiolus) demissa attaches itself to the roots of cord grass and other hard objects in tidal salt marshes by spinning adhesive byssal threads. The precursor of a protein apparently present in the adhesive plaques of the threads was isolated in quantity from the foot of the mussel. The protein has an apparent molecular weight of 130,000, a pI of 8.1, and contains a high proportion of Gly, Glu/Gln, Lys and 3,4-dihydroxyphenyl-L-alanine (DOPA). Sequence of tryptic peptides suggests a pattern of repeated motifs, such as: Gly--DOPA--Lys, and X--Gly--DOPA--Y--Z--Gly--DOPA/Tyr--Lys, where X is Thr or Ala in octapeptides and Gln--Thr in nonapeptides. Y is variable, but more often than not hydrophobic; and Z is frequently Pro or 4-trans-hydroxyproline (Hyp). The presence of Pro--Gly and Hyp--Gly sequences of delta-hydroxylysine in the protein is reminiscent of typical collagens; however, the protein is not labile to clostridial collagenase, nor does collagen cross-react with antibodies raised against the mussel protein. Unlike typical collagens, Gly probably occurs only at every 4th or 5th residue in this unusual mussel protein.

Cloning of full-length elastin cDNAs from a human skin fibroblast recombinant cDNA library: further elucidation of alternative splicing utilizing exon-specific oligonucleotides

A human cDNA library was constructed utilizing RNA isolated from cultured skin fibroblasts. Recombinant clones containing elastin sequences were identified by plaque hybridizations with previously characterized human placental elastin cDNAs. Seven positive recombinant clones with inserts of approximately 3.2-2.2 kb were isolated. Characterization of the clones by restriction endonuclease analysis and dot-blot hybridizations with exon-specific synthetic oligonucleotides demonstrated considerable variability in the primary nucleotide sequence. Dideoxy nucleotide sequencing confirmed this finding. The variability is most likely a result of alternative splicing of exons from the primary elastin transcripts. The two largest clones contained approximately 1 kb of 3' untranslated sequence and approximately 2.2 kb of translated sequence encoding 730 amino acids. Six amino acids, encoded by exon 12A, have not been previously noted in human elastin cDNAs. In addition, these human skin fibroblast clones contained a 49 bp 5' untranslated sequence. These results demonstrate that there is considerable variability in the processed nucleotide sequence of the elastin mRNAs. These transcripts may code for isoforms of tropoelastin with different biologic properties.

Biochemical study of adduct synthesis between fibrin monomers and elastin

Monomers of fibrin generated by thrombin from fibrinogen reacted with elastin to give a new addition product or adduct. Adduct formation resulted from a covalent bond between fibrin monomers and elastin. The kinetic studies of this reaction confirmed that the adduct was formed before fibrin precipitated to produce the clot. The reaction depended on elastin, fibrinogen and thrombin concentrations. When thrombin-induced and reptilase-induced fibrin were compared, it became obvious that fibrin monomers did intervene more commonly as Des AA-fibrin than as Des AA.BB-fibrin. The adduct synthesis was completely inhibited by 150 microM of the peptide Gly-Pro-Arg-Pro which was previously known to stabilize the fibrin monomers and consequently to inhibit the polymerization completely. It is shown that FXIII could intervene directly in the reaction where homological quality of elastin (human versus bovine) and purity of thrombin were other important factors.

Characterization of human skin fibroblasts elastase activity

We present evidence that enzyme activity hydrolyzing Succinoyl trialanine paranitroanilide (Suc(Ala)3NA) expressed by Human Skin Fibroblasts (HSF) in culture could be attributed to the concerted action of an endopeptidase and an aminopeptidase(s). Both endopeptidase and aminopeptidase activities were strongly inhibited by metal chelating agents and Copper and Zinc ions but were insensitive to Tissue Inhibitor of Metallo Proteases (TIMP). These protease activities coeluted on ion exchange chromatography (DEAE Tris acryl M) and were further separated by high-performance liquid chromatography HPLC (TSK 3000 SW). The endopeptidase activity, designated as HSF E1, was eluted at the position corresponding to an Mr equal to 94,000. It has only a limited elastinolytic potential as evaluated on 3H insoluble elastin, but it extensively degrades human skin elastic fibers as directly assessed on human skin tissue sections and further quantitated by automated image analysis. The level of HSF E1 increases with the number of fibroblast passages.

Multiple chick tropoelastin mRNAs

Several overlapping chick tropoelastin cDNAs were isolated from a lambda gt11 cDNA library constructed from whole 10 day chick embryo total RNA. Comparison of the nucleotide sequence of the 2.3 kb tropoelastin cDNA to the sequences published by Bressan et al. (1) and Tokimitsu et al. (2) revealed the presence of two inserts (72 and 30 base pairs) in the cDNA derived from embryonic tissue. Northern blot analysis of 14 day embryonic aortae RNA with tropoelastin cDNA clones showed hybridization to a 3.5 kb mRNA. However, S1 nuclease protection experiments performed on RNA extracted from the same tissue showed that at least two if not more tropoelastin mRNAs exist and that the proportion of each varies in the ages examined. These results provide an origin and substantiate the differential expression of the multiple tropoelastin polypeptides found in developing chick aortic tissue.

Structure and elasticity of microtubule-associated protein tau

Tau is one of the diverse group of microtubule-associated proteins that bind to microtubules and may thereby influence their structure and function. It occurs in the mammalian brain, mainly in axons, and is a component of the neurofibrillary tangles of Alzheimer's disease. Tau was recently sequenced, but there remains a short-age of structural data on the protein. We have now prepared paracrystals of tau suitable for electron microscopy and image processing. They show distinct transverse banding and polarity, indicating that the protein subunits are aligned with the same orientations. In contrast to other paracrystals, those of tau protein can stretch or contract continuously by more than three-fold; the axial repeats range from 22 to 68 nm. After scaling to a common period, the density distributions are closely superimposable. This suggests that tau is an elastic molecule.

Comparative investigations of partial amino acid sequences of prolamins and glutelins from cereals. VIII. Amino acid sequences of glutelin peptides

The peptide fractions isolated from chymotryptic hydrolysates of wheat, rye and barley glutelins were separated by high-performance liquid chromatography on octadecyl silica gel. The peptides obtained were analysed for their amino acid composition and some also for their amino acid sequence. Characteristic sequences of peptides from wheat glutelin can be grouped into three types. The first type contains a high amount of Gly and frequently Tyr in the N-terminal positions. A typical partial sequence, which occurs repeated in two peptides, is QGQQPGQGQ. Sequences of this type are found in high-molecular-weight subunits. The second type is characterized by the sequence SQn (n = 3-5) followed by a hydrophobic tripeptide e.g., PPF, PVL; the most frequent sequence is SQQQQPPF. Low-molecular-weight subunits contain sequences of this type. The third type, which has partial sequences such as QQPQQPFP, corresponds to typical peptides from prolamin. Most sequences of peptides from rye and barley glutelins can be divided into two groups. The predominant type shows prolamin-like sequences, e.g., PQQPXPQQ with X being F or I. The second type is similar to glycine-rich peptides from wheat glutelin, except that repeating sequences are less frequent.

In vitro processing of tropoelastin: investigation of a possible transport function associated with the carboxy-terminal domain

In vitro translation systems were used to characterize the processing of bovine tropoelastin isoforms and to investigate the possibility that the carboxy-terminal 19 amino acids of tropoelastin encode a molecular domain that directs intracellular transport. Immunoprecipitation with domain-specific antibodies demonstrated that multiple tropoelastin isoforms corresponding to those identified in tissue and cell culture studies were correctly translated and were processed by dog pancreas microsomes. Our results demonstrate that all tropoelastin isoforms are translocated completely into the microsomal vesicle and do not remain associated with the microsomal membrane. These results exclude the possibility that the carboxy-terminal domain of tropoelastin functions as a trafficking signal by effecting an association between tropoelastin and an intracellular membraneous compartment.

Elastin mRNA levels and insoluble elastin accumulation in neonatal rat smooth muscle cell cultures

Insoluble elastin accumulation, elastin mRNA translational efficiencies, and elastin mRNA levels were evaluated in cultures of neonatal rat aortic smooth muscle cells grown for several days in consecutive passages. When the products of in vitro translation were immunoprecipitated with an anti-alpha-elastin antibody, a single 79,000-Da protein was obtained. Northern blot analysis also indicated an elastin mRNA species corresponding to approximately 4.2 kilobases. Insoluble elastin accumulation increased in cells cultured for 7-21 days in first through fourth passages, while with one exception, relative levels and translational activity of elastin mRNA decreased with time in culture. The data indicated that a simple relationship between elastin accumulation and elastin mRNA levels was not evident.

The elastin receptor: a galactoside-binding protein

The elastin receptor complex contains a component of 67 kilodaltons that binds to a glycoconjugate affinity column containing beta-galactoside residues and is eluted from this column with lactose. This protein component is also released from the surface of cultured chondroblasts by incubation with lactose, and its association with immobilized elastin is inhibited by lactose. Since lactose also blocks elastic fiber formation by cultured chondroblasts, the galactoside-binding property of the elastin receptor is implicated in this process.

Evidence for the existence of three chick lung tropoelastins

Three tropoelastin polypeptides are identified among the cell-free translation products of chick embryo lung mRNAs and organ cultures extracts. The tropoelastins are distinguished by one and two dimensional gel electrophoretic systems and are all immunoreactive with monospecific chick tropoelastin antiserum. The ratio of the three tropoelastins does not vary significantly between 10 and 16 days of lung embryogenesis. The third tropoelastin (c) is found to co-migrate with tropoelastin b on SDS-polyacrylamide gel electrophoresis but is visible after cyanogen bromide cleavage of reticulocyte lysate proteins. Immunoprecipitates from lung organ culture also contain tropoelastins a, b and c.