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PubMed2002

The molecular basis of the coloration mechanism in lobster shell: beta-crustacyanin at 3.2-A resolution.

The binding of the carotenoid astaxanthin (AXT) in the protein multimacromolecular complex crustacyanin (CR) is responsible for the blue coloration of lobster shell. The structural basis of the bathochromic shift mechanism has long been elusive. A change in color occurs from the orange red of the unbound dilute AXT (lambda(max) 472 nm in hexane), the well-known color of cooked lobster, to slate blue in the protein-bound live lobster state (lambda(max) 632 nm in CR). Intriguingly, extracted CR becomes red on dehydration and on rehydration goes back to blue. Recently, the innovative use of softer x-rays and xenon derivatization yielded the three-dimensional structure of the A(1) apoprotein subunit of CR, confirming it as a member of the lipocalin superfamily. That work provided the molecular replacement search model for a crystal form of the beta-CR holo complex, that is an A(1) with A(3) subunit assembly including two bound AXT molecules. We have thereby determined the structure of the A(3) molecule de novo. Lobster has clearly evolved an intricate structural mechanism for the coloration of its shell using AXT and a bathochromic shift. Blue/purple AXT proteins are ubiquitous among invertebrate marine animals, particularly the Crustacea. The three-dimensional structure of beta-CR has identified the protein contacts and structural alterations needed for the AXT color regulation mechanism.

Amino Acid Sequence↗

PubMed1970

The total amino acid content of fossil pecten shells.

Amino acid analyses have been made of the insoluble protein, soluble peptide, and free amino acid fractions isolated from a series of fossil pecten shells of ages from the Pleistocene through the Jurassic. The total amino acid content declines progressively with age of the fossil but, in contrast to oyster shells, only a small fraction of the initial protein is present in the Pleistocene and older specimens. Though the thermally less stable acids are depleted in the free acid fraction, this is not true for the insoluble proteins and peptides. Large amounts of free amino acids and peptides persist through the Pliocene, considerable quantities of peptide have been recovered from the Miocene specimens, and even the oldest fossils have retained analyzable amounts of all three fractions.

Amino Acids↗

PubMed1995

Calcium signaling in a narrow somatic submembrane shell during synaptic activity in cerebellar Purkinje neurons.

Temporal and spatial changes in the intracellular Ca2+ concentration ([Ca2+]i) were examined in dendrites and somata of rat cerebellar Purkinje neurons by combining whole-cell patch-clamp recording and fast confocal laser-scanning microscopy. In cells loaded via the patch pipette with the high-affinity Ca2+ indicator Calcium Green-1 (Kd approximately 220 nM), a single synaptic climbing fiber response, a so-called complex spike, resulted in a transient elevation of [Ca2+]i that showed distinct differences among various subcellular compartments. With conventional imaging, the Ca2+ signals were prominent in the dendrites and almost absent in the soma. Confocal recordings from the somatic region, however, revealed steep transient increases in [Ca2+]i that were confined to a submembrane shell of 2- to 3-microns thickness. In the central parts of the soma [Ca2+]i increases were much slower and had smaller amplitudes. The kinetics and amplitudes of the changes in [Ca2+]i were analyzed in more detail by using the fast, low-affinity Ca2+ indicator Calcium Green-5N (Kd approximately 17 microM). We found that brief depolarizing pulses produced [Ca2+]i increases in a narrow somatic submembrane shell that resembled those seen in the dendrites. These results provide direct experimental evidence that the surface-to-volume ratio is a critical determinant of the spatiotemporal pattern of Ca2+ signals evoked by synaptic activity in neurons.

Animals↗

PubMed1997

Molecular cloning and characterization of lustrin A, a matrix protein from shell and pearl nacre of Haliotis rufescens.

A specialized extracellular matrix of proteins and polysaccharides controls the morphology and packing of calcium carbonate crystals and becomes occluded within the mineralized composite during formation of the molluscan shell and pearl. We have cloned and characterized the cDNA coding for Lustrin A, a newly described matrix protein from the nacreous layer of the shell and pearl produced by the abalone, Haliotis rufescens, a marine gastropod mollusc. The full-length cDNA is 4,439 base pairs (bp) long and contains an open reading frame coding for 1,428 amino acids. The deduced amino acid sequence reveals a highly modular structure with a high proportion of Ser (16%), Pro (14%), Gly (13%), and Cys (9%). The protein contains ten highly conserved cysteine-rich domains interspersed by eight proline-rich domains; a glycine- and serine-rich domain lies between the two cysteine-rich domains nearest the C terminus, and these are followed by a basic domain and a C-terminal domain that is highly similar to known protease inhibitors. The glycine- and serine-rich domain and at least one of the proline-rich domains show sequence similarity to proteins of two extracellular matrix superfamilies (one of which also is involved in the mineralized matrixes of bone, dentin, and avian eggshell). The arrangement of alternating cysteine-rich domains and proline-rich domains is strikingly similar to that found in frustulins, the proteins that are integral to the silicified cell wall of diatoms. Its modular structure suggests that Lustrin A is a multifunctional protein, whereas the occurrence of related sequences suggest it is a member of a multiprotein family.

Amino Acid Sequence↗

PubMed2000

Mucins and molluscan calcification. Molecular characterization of mucoperlin, a novel mucin-like protein from the nacreous shell layer of the fan mussel Pinna nobilis (Bivalvia, pteriomorphia).

A cDNA expression library constructed from mantle tissue mRNA of the Mediterranean fan mussel Pinna nobilis was screened with antibodies raised against the acetic acid-soluble shell matrix of the same species. This resulted in the isolation of a 2138-base pair cDNA, containing 13 tandem repeats of 93 base pairs. The deduced protein has a molecular mass of 66.7 kDa and a isoelectric point of 4.8. This protein, which is enriched in serine and proline residues, was overexpressed, purified, and used for producing polyclonal antibodies. Immunological in situ and in vitro tests showed that the protein is localized in the nacreous aragonitic layer of P. nobilis, but not in the calcitic prisms. Because this protein of the nacre of P. nobilis exhibits some mucin-like characteristics, we propose the name mucoperlin. This is the first paper reporting the cloning of a molluscan mucin and the first molecular evidence for the involvement of a mucin in molluscan calcification. This finding corroborates our previous hypothesis that some of the proteinaceous constituents of the molluscan shell matrix would derive from mucins, common to many metazoan lineages of the late Precambrian (Marin, F., Smith, M., Isa, Y., Muyzer, G. and Westbroek, P. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1554-1559). The adaptation of an ancestral mucin to a new function, the regulation of the mineralization process, may be one of the molecular events, among others, that would explain the simultaneous emergence of organized calcification in many metazoan lineages during the Cambrian explosion.

Amino Acid Sequence↗

PubMed2005

Caspartin and calprismin, two proteins of the shell calcitic prisms of the Mediterranean fan mussel Pinna nobilis.

We used the combination of preparative electrophoresis and immunological detection to isolate two new proteins from the shell calcitic prisms of Pinna nobilis, the Mediterranean fan mussel. The amino acid composition of these proteins was determined. Both proteins are soluble, intracrystalline, and acidic. The 38-kDa protein is glycosylated; the 17-kDa one is not. Ala, Asx, Thr, and Pro represent the dominant residues of the 38-kDa protein, named calprismin. An N-terminal sequence was obtained from calprismin. This sequence, which comprises a pattern of 4 cysteine residues, is not related to any known protein. The second protein, named caspartin, exhibits an unusual amino acid composition, since Asx constitutes by far the main amino acid residue. Preliminary sequencing surprisingly suggests that the first 75 N-terminal residues are all Asp. Caspartin self-aggregates spontaneously into multimers. In vitro tests show that it inhibits the precipitation of calcium carbonate. Furthermore, it strongly interferes with the growth of calcite crystals. A polyclonal antiserum raised against caspartin was used to localize this protein in the shell by immunogold. The immunolocalization demonstrates that caspartin is distributed within the prisms and makes a continuous film at the interface between the prisms and the surrounding insoluble sheets. Our finding emphasizes the prominent role of aspartic acid-rich proteins for the building of calcitic prisms among molluscs.

Amino Acid Sequence↗

PubMed2006

The structure of beta-carbonic anhydrase from the carboxysomal shell reveals a distinct subclass with one active site for the price of two.

CsoSCA (formerly CsoS3) is a bacterial carbonic anhydrase localized in the shell of a cellular microcompartment called the carboxysome, where it converts HCO(3)(-) to CO(2) for use in carbon fixation by ribulose-bisphosphate carboxylase/oxygenase (RuBisCO). CsoSCA lacks significant sequence similarity to any of the four known classes of carbonic anhydrase (alpha, beta, gamma, or delta), and so it was initially classified as belonging to a new class, epsilon. The crystal structure of CsoSCA from Halothiobacillus neapolitanus reveals that it is actually a representative member of a new subclass of beta-carbonic anhydrases, distinguished by a lack of active site pairing. Whereas a typical beta-carbonic anhydrase maintains a pair of active sites organized within a two-fold symmetric homodimer or pair of fused, homologous domains, the two domains in CsoSCA have diverged to the point that only one domain in the pair retains a viable active site. We suggest that this defunct and somewhat diminished domain has evolved a new function, specific to its carboxysomal environment. Despite the level of sequence divergence that separates CsoSCA from the other two subclasses of beta-carbonic anhydrases, there is a remarkable level of structural similarity among active site regions, which suggests a common catalytic mechanism for the interconversion of HCO(3)(-) and CO(2). Crystal packing analysis suggests that CsoSCA exists within the carboxysome shell either as a homodimer or as extended filaments.

Amino Acid Sequence↗

PubMed1999

Effects of phosphate, prostaglandins, arachidonic acid and arginine vasotocin on oviposition and pigment secretion from the shell gland in Japanese quail.

1. Phosphate solution, prostaglandin F2alpha and E2, arachidonic acid and arginine vasotocin were injected intrauterinely or intravenously into laying quail hens 6 h before expected oviposition. Following injections, induced ovipositions and secretions of pigment from their shell glands were observed. 2. The effects of intrauterine injection with prostaglandins, which induced oviposition and pigment secretion, were not inhibited by pre-injection of indomethacin. 3. Indomethacin completely inhibited the inducing effects on oviposition and pigment secretion of intrauterine injections with phosphate solution and arachidonic acid. 4. Intravenous injection with arginine vasotocin or prostaglandins also induced oviposition and pigment secretion; indomethacin, however, only inhibited pigment secretion. 5. It is concluded that the effects of prostaglandins on pigment secretion from the shell gland were demonstrated experimentally.

Animals↗

PubMed1988

Monte-Carlo simulation of DNA duplex hydration. B and B' conformations of poly(dA).poly(dT) have different hydration shells.

Monte-Carlo simulation of poly(dA).poly(dT) hydration by 30 water molecules per nucleotide pair has been performed. Two B-family conformations, both with a 36 degrees helical twist but with different minor groove widths, were considered. One conformation is Arnott's standard B form, the other one is specific for poly(dA).poly(dT) B' form with a narrowed minor groove. The mean energies and the mean numbers of water-water and water-DNA hydrogen bonds are close for the two conformations. Nevertheless, the hydration shell of the B' form differs drastically from that of the standard B form. The water arrangement in the minor groove of the B' form resembles the spine of hydration in the central part of Dickerson's dodecamer d(CGCGAATTCGCG). No such spine is formed in the hydration shell of the usual B form with a wider minor groove. In this conformation water bridges between adenine N3 or thymine O2 and oxygen of the sugar ring of the neighbouring nucleotide along the chain can be formed ("strings" in Dickerson's decamer d(CCAAGATTGG].

DNA↗

PubMed1999

Interactions of hydrated IIa and IIb group metal cations with thioguanine-cytosine DNA base pair: Ab initio and density functional theory investigation of polarization effects, differences among cations, and flexibility of the cation hydration shell.

The structures and energies of the thioguanine-cytosine Watson-Crick (thioGC WC) base pair interacting with hydrated IIa (Mg2+, Ca2+, Ba2+) and IIb group (Zn2+, Cd2+, Hg2+) cations have been studied using ab initio techniques. Furthermore, complexes between guanine and thioguanine with hydrated cations have been characterized assuming various structures of the hydration shells. The complexes of the thioGC WC base pair with hydrated cations have similar properties as the previously studied GC WC base pair. There is substantial polarization stabilization of the base pairing due to cation binding which amounts to 7 - 11 kcal/mol. Soft Cd2+ and Hg2+ cations have a uniquely strong interaction with the thiogroup and induce substantial nonplanarity of the pairing. The thiogroup tends to reduce the number of water molecules in the first hydration shell of the cation. All complexes were optimized within the Hartree-Fock (HF) approximation while their energetics has been evaluated using the second-order Moller-Plesset perturbational method (MP2). All interaction energy evaluations and a substantial portion of the optimizations of the hydrated cation-(thio)guanine complexes have been repeated using Becke-3LYP Density Functional Theory method. All three approximations used (HF, Becke-3LYP, and MP2) give qualitatively the same results for the present cationic complexes. The results demonstrate specific differences among the cations and provide a set of reference structures and energies for verification and/or parametrization of empirical potentials and other theoretical methods.

Barium↗

PubMed1992

Induction of chromosome aberrations by monochromatic X-rays with resonance energy of phosphorus K-shell absorption edge.

The induction of chromosome aberrations by monochromatic soft X-rays with energies corresponding to the K-shell absorption edge of phosphorus has been studied in density-inhibited mouse m5S cells. The frequency of dicentrics was markedly enhanced when the cells were irradiated with energy at the K-shell resonance peak (2.153 keV) as compared to those at below (2.146 keV) or above (2.160 keV) the peak. The quantum efficiency was calculated to be 2.7 x 10(-3) for the induction of dicentrics per photoelectric absorption of phosphorus atom in DNA, which was comparable to the known efficiencies of X- or gamma-ray-induced DNA double-strand breaks. However, comparison of the efficiencies based on the absorbed dose indicated that the magnitude of the enhancement was not due solely to the selective photoelectric absorption of the phosphorus atoms in DNA, and suggested the combined contributions of Auger electrons from phosphorus atoms within and outside the DNA molecules.

Animals↗

PubMed2005

A shell finite element model of the pelvic floor muscles.

The pelvic floor gives support to the organs in the abdominal cavity. Using the dataset made public in (Janda et al. J. Biomech. (2003) 36(6), pp. 749-757), we have reconstructed the geometry of one of the most important parts of the pelvic floor, the levator ani, using NURB surfaces. Once the surface is triangulated, the corresponding mesh is used in a finite element analysis with shell elements. Based on the 3D behavior of the muscle we have constructed a shell that takes into account the direction of the muscle fibers and the incompressibility of the tissue. The constitutive model for the isotropic strain energy and the passive strain energy stored in the fibers is adapted from Humphrey's model for cardiac muscles. To this the active behavior of the skeletal muscle is added. We present preliminary results of a simulation of the levator ani muscle under pressure and with active contraction. This research aims at helping simulate the damages to the pelvic floor that can occur after childbirth.

Computer Simulation↗

PubMed1958

Studies on shell formation. VIII. Electron microscopy of crystal growth of the nacreous layer of the oyster Crassostrea virginica.

Electron microscope observations have been made by means of the replica method on growth processes of calcite crystals of the nacreous layer of the shell of the oyster, Crassostrea virginica. Layer formation is initiated by the secretion of a conchiolin matrix and the deposition of rounded crystal seeds on or in this material. In some areas crystal seeds are elongate and within a given area show a similar orientation, probably due to slower deposition. The seeds appear to increase in size by dendritic growth, and smaller seeds become incorporated into larger ones which come into contact to form a single layer. With further growth, crystals overlap, forming a step-like arrangement. The direction of growth is frequently different in neighboring regions. Crystal seeds deposited on crystal surfaces are usually elongate and oriented. Well developed crystals have a tabular idiomorphic form and are parallel in their growth. Rounded and irregular crystals were also observed. The crystals show reticular structure with units of the order of 100 A and striations corresponding with the rhombohedral axes of the crystals. The role of the mantle is discussed in relation to the growth patterns of crystals and shell structure.

Animals↗

PubMed1961

Studies on shell formation. IX. An electron microscope study of crystal layer formation in the oyster.

Details of crystal growth in the calcitostracum of Crassostrea virginica have been studied with the purpose of analyzing the formation of the overlapping rows of oriented tabular crystals characteristic of this part of the shell. Crystal elongation, orientation, and dendritic growth suggest the presence of strong concentration gradients in a thin layer of solution in which crystallization occurs. Formation of the overlapping rows can be explained by three processes observed in the shell: a two-dimensional tree-like dendritic growth in which one set of crystal branchings creeps over an adjacent set of branchings; three-dimensional dendritic growth; and growth by dislocation of crystal surfaces. Multilayers of crystals may thus be formed at one time. This is favored by infrequent secretion of a covering organic matrix which would inhibit crystal growth. The transitional zone covering the outer part of the calcitostracum and the inner part of the prismatic region is generally characterized by aggregates of small crystals with definite orientation. Growth in this zone appears to take place in a relatively homogeneous state of solution without strong concentration gradients. Thin membranes and bands of organic matrix were commonly observed in the transitional zone bordering the prismatic region. The membrane showed a very fine oriented network pattern.

Animals↗

PubMed1987

High-resolution images of the L1551 bipolar outflow: evidence for an expanding, accelerated shell.

Approximately one-half of the L1551 bipolar outflow was mapped in the J = 1-0 transition of 12CO using the FCRAO 14 m telescope. The data were obtained by heavily oversampling over the beam area and then were reconstructed using a maximum entropy algorithm to obtain images of the high-velocity gas with an angular resolution of approximately 20". The outflow exhibits a striking shell-like structure with the lowest velocity out-flowing gas found along the limb of the outflow, and the highest velocity outflowing gas found along the axis of the outflow. A smooth transition is found between low-velocity emission on the periphery and high-velocity gas in the center. Our data can be modeled by molecular material located in a thin expanding shell which is accelerating away from IRS 5.

Astronomical Phenomena↗

PubMed1999

The Detached Dust Shell around the Massive Star HD 179821.

We have used the Keck I telescope to resolve at three mid-IR wavelengths the emission from HD 179821 (= RAFGL 2343), a G-type supergiant of perhaps 30 M middle dot in circle with a detached dust shell. The shell is very approximately circular in shape with an inner diameter of approximately 3&farcs;3, corresponding to 3.0x1017 cm. We estimate that the star was losing approximately 4x10-4 M middle dot in circle yr-1 until about 1800 yr ago, when the mass loss slowed dramatically. During the past approximately 104 yr, the star has lost approximately 10% of its initial mass. The star lies about 0&farcs;35 off center and is closer to the brighter, northern hemisphere of the nebula, which can be explained if the outflow velocity Vinfinity deviates by +20% from the average in the southern hemisphere and -20% from the average in the northern hemisphere. The mass-loss rate M&d2;(straight theta) may have been inversely correlated with the outflow velocity so that the momentum outflow p&d2; was isotropic during the mass-loss phase. It also seems that M&d2;totalVinfinity was within a factor of 2 of L*/c, where L* is the current luminosity of the star; the mass loss may have been driven by radiation pressure. These results may help characterize the asymmetric circumstellar winds into which supernova explosions propagate.

Journal Article↗

PubMed2000

Spherical Oscillatory alpha2 Dynamo Induced by Magnetic Coupling between a Fluid Shell and an Inner Electrically Conducting Core: Relevance to the Solar Dynamo.

A two-layer spherical alpha2 dynamo model consisting of an inner electrically conducting core (magnetic diffusivity lambdai and radius ri) with alpha=0 surrounded by an electrically conducting spherical shell (magnetic diffusivity lambdao and radius ro) with a constant alpha is shown to exhibit oscillatory behavior for values of beta=lambdai&solm0;lambdao and ri&solm0;ro relevant to the solar dynamo. Time-dependent dynamo solutions require ri&solm0;ro>/=0.55 and beta</=O&parl0;1&parr0;. For the Sun, ri&solm0;ro is about 0.8 and beta approximately 10-3. The timescale of the oscillations matches the 22 yr period of the sunspot cycle for lambda0=O(102 km2 s-1). It is unnecessary to hypothesize an alpha-omega dynamo to obtain oscillatory dynamo solutions; an alpha2 dynamo suffices provided the spherical shell region of dynamo action lies above a large, less magnetically diffusive core, as is the case for the solar dynamo.

Journal Article↗

PubMed1997

Calculation of the dose distribution in water from 71Ge K-shell x-rays.

The dose distribution in water from 71Ge K-shell x-rays (Eave = 9.44 keV) was calculated for various source configurations using both analytic and EGS4 Monte Carlo calculations. The point source kernel and the buildup factor are presented. The buildup factor for a point source in water has been found to increase up to about 1.1 as radial distance approaches 1 cm. Comparison between 71Ge and 90Sr/Y shows a similarity between their relative dose distribution in water. The dose distribution from a disc source was calculated using the EGS4 code and compared with the results from analytic calculation. Excellent agreement was observed, confirming the validity of analytic calculations. The dose rate at 0.01 cm from a 71Ge disc source was calculated to be about 1.3 x 10(-5) Gy MBq-1 s-1. Based on the results from this study, 71Ge activity of the order of 3.7 x 10(10) Bq (approximately 1 Ci) might be necessary to obtain dose rates typical of 90Sr/Y ophthalmic applicators. The possibility of using 71Ge as a source of radioactive stents was also investigated. A 71Ge stent was modelled as a cylindrical shell source and the dose rates were determined by Monte Carlo calculations. Some calculated results are compared with published values for a 32P-coated stent. The dose rate at 0.01 cm from a 71Ge stent has been calculated to be about 6.5 x 10(-3) Gy MBq-1 h-1, which is much lower than the reported dose rate at the same distance from a 32P-coated stent. However, an initial source activity of the order of 3.7 x 10(7) Bq (approximately 1 mCi) would easily result in a typical target dose (approximately 24 Gy) needed for intravascular stent applications. In conclusion, 71Ge sources could be used as alternatives to beta sources and, unlike high-energy (approximately MeV) beta sources, may provide easily predictable dose distributions in heterogeneous media and low dose rates, which might be beneficial for some clinical applications.

Beta Particles↗