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At least 19 recordsLinked to original sources
PubMed2026

Structural Characterization and Engineering of a GH134 β-Mannanase from Aspergillus nidulans for Enhancement of Activity and Stability.

Mannans are abundant plant hemicelluloses, and endo-β-mannanases are important biocatalysts for their conversion into functional manno-oligosaccharides. Here, we report the structural and functional characterization of a glycoside hydrolase family 134 β-mannanase from Aspergillus nidulans (AnGH134) and a structure-guided engineering strategy to improve its performance on locust bean gum. The 1.75 Å crystal structure reveals the conserved lysozyme-like fold of GH134 enzymes and supports an inverting catalytic mechanism with Glu43 and Asp55 as the putative catalytic residues. Docking, mutational, and molecular dynamics analyses indicate that AnGH134 uses an extended substrate-binding groove and that groove-exit residues and the C-terminal region contribute to productive catalysis. Guided by these findings, N-terminal fusion of CBM10 enhanced catalytic efficiency and thermal stability, whereas C-terminal fusion was detrimental. These results provide a framework for engineering GH134 mannanases.

Aspergillus nidulans↗
PubMed2026

The twofold cost of sex reconsidered: meiotic mechanisms protect anisogamous populations from invasion by thelytoky.

Most multicellular animals practice anisogamy (fertilization between eggs and sperm). When mothers produce sons and daughters at a 1:1 ratio, the "twofold cost of males" arises because males do not directly contribute to population growth. If thelytokous parthenogens producing only daughters invade a population, they should spread rapidly. Although thelytoky has repeatedly evolved across invertebrate and vertebrate taxa, it remains a minority. Why? The evolutionary transition from anisogamy to thelytoky requires eggs to initiate embryonic development without fertilization. However, in metazoan animals, meiotic metaphase (MM) arrest halts oogenesis midway and normally resumes only after stimulation by sperm penetration. Empirical and experimental evidences indicate that release of MM arrest without fertilization is extremely difficult, providing a strong mechanistic barrier against parthenogenesis. Even if MM arrest were released, oogenesis would proceed to produce either a haploid embryo or a diploid embryo through refusion with the second polar body (terminal fusion automixis). Outbred species typically accumulate more than one lethal equivalent of recessive deleterious alleles per genome as heterozygotes. Upon transition to haploid or automictic development, these recessive lethals normally masked in outbred diploids would be exposed simultaneously, causing embryonic death and creating the next barrier. Thus, thelytoky cannot be achieved simply by modification of the existing meiotic system; instead, other mechanisms, such as apomixis, that bypass meiosis are required. Mathematical models and simulations support this "meiotic constraint" hypothesis. Combined with recently proposed immediate benefits of anisogamy and traditional genetic benefits (e.g., Red Queen), it may largely explain the maintenance of costly anisogamy.

Animals↗
PubMed2026

C-Terminal Truncation and Fusion Partner Determine Oncogenicity of FGFR3.

UNLABELLED: Genomic alterations affecting components of the fibroblast growth factor (FGF) signaling axis can trigger aberrant pathway activation and tumor development. Genomic truncation of the FGF receptor 2 (FGFR2) exon 18 (E18) disrupts the FGFR2 carboxy (C)-terminal tail, acting as a potent driver alteration across multiple tumor types. In this study, we analyzed human oncogenomic datasets to reveal that E18 truncations are similarly prevalent in FGFR3, an FGFR2 paralog. FGFR3 E18 truncations primarily occur due to rearrangements (RE) that involve transforming acidic coiled-coil-containing protein 3 (TACC3), resulting in FGFR3ΔE18-TACC3 gene fusions. In contrast to E18-truncated FGFR2, functional in vitro and in vivo examination of Fgfr3 variants demonstrated that the truncation of Fgfr3 E18 is insufficient to promote oncogenic activity in cell lines or in the lungs and mammary glands of mice. Only the combination of an Fgfr3 E18 truncation with a RE partner gene that encodes a receptor-dimerizing domain resulted in the development of tumors, which were sensitive to FGFR inhibition. Overall, these findings suggest that patients with cancers that are positive for rearranged FGFR3, resulting in E18 truncation and a fusion to dimerizing partners, should be considered for FGFR-targeted therapies. SIGNIFICANCE: FGFR3, unlike its paralog FGFR2, requires both a C-terminal truncation and fusion to a partner gene that retains the expression of a dimerizing domain to effectively drive oncogenic signaling and tumorigenesis.

Receptor, Fibroblast Growth Factor, Type 3↗
PubMed1978

Recurrent sustained ventricular tachycardia. 1. Mechanisms.

The mechanism of recurrent sustained ventricular tachycardia (VT) was evaluated in 21 patients. Re-entry as the mechanism for VT was suggested by a) the reproducible initiation (19) and termination (15) of the arrhythmia by programmed stimulation. The rate, ventricle of origin, and stimulation site determined the method of termination. One VPD was usually required with VT rates less than 175/min and/or ventricle of origin ipsilateral to the stimulation site, while two VPDs were usually required for VT with faster rates originating in a contralateral ventricle. The proximal His-Purkinje system (HPS) was not required for initiation or maintenance of VT. Evidence localizing the site of re-entry to a small portion of the ventricles included: a) ventricular capture by ventricular premature depolarizations (VPDs) or pacing (VP) without terminating VT (5), b) sinus capture following VPDs and/or supraventricular fusions without terminating VT (12), and c) atrial pacing normalizing the QRS and H-V intervals without terminating VT (5).

Adolescent↗
PubMed1976

Assembly of the sarcoplasmic reticulum. Biosynthesis of the adenosine triphosphatase in rat skeletal muscle cell culture.

Temporal patterns of biosynthesis of the Ca2+ + Mg2+-dependent adenosine triphosphatase of sarcomplasmic reticulum were obtained from studies with primary cultures of rat skeletal muscle cells. Rates of synthesis at various stages of differentiation were estimated from the incorporation of tritium-labeled leucine into the ATPase. Cells were solubilized with detergent, and newly synthesized ATPase was isolated from cells by antibody precipitation in the presence of carrier ATPase. Radioactivity incorporated into the ATPase was determined after gel electrophoresis of the precipitates and counting of gel slices containing the ATPase band. In Dulbecco's modified Eagle's medium containing 10% horse serum and 0.5% chick embryo extract, mononucleated myoblast cells began to form multinucleated myotubes after about 50 hours in culture. Prior to fusion little ATPase synthesis was detectable; during fusion the ATPase was synthesized at an accelerating rate for a period of about 30 hours. The rate of synthesis levelled off after about 90 hours coincident with termination of fusion. In Dulbecco's modified Eagle's medium containing 20% fetal calf serum and 8% embryo extract, the onset of fusion was delayed for 30 to 40 hours. In this medium biosynthesis of the ATPase was also delayed so that biosynthesis of the ATPase appeared to be correlated with fusion of muscle cells. Cells cultured in Culbecco's modified Eagle's medium containgin 10% horse serum, but only 60 muM Ca2+, proliferated but did not fuse. Under these conditions, synthesis of the ATPase was measurable at 50 to 60 hours, and the rate of synthesis accelerated until 120 hours when it declined. Under all conditions degradation of the ATPase occurred with a half-life of 20 hours whereas the half-life of total protein degradation was 40 hours. Synthesis of the sarcoplasmic reticulum ATPase, like that of a number of other muscle-specific proteins, is greatly accelerated as myoblasts fuse and differentiate into myotubes. Fusion is not essential for this phenomenon, however, although it is normally concomitant with it.

Adenosine Triphosphatases↗
PubMed1978

Purification of the fusion protein of Sendai virus: analysis of the NH2-terminal sequence generated during precursor activation.

The two glycoproteins of Sendai virus, the hemagglutinin-neuraminidase and the fusion protein (F), were separated and purified by affinity chromatography on a Lens culinaris lectin-Sepharose column. F was shown to consist of two disulfide-bonded glycopolypeptide chains, F1 and F2, of molecular weights 51,000 and 11,000, each of which contained 15% carbohydrate by weight. Amino-terminal sequence analysis showed that F2 was blocked and that the hydrophobic sequence NH2-Phe-Phe-Gly-Ala-Val-Ile-Gly-Ile-Ile-Ala-Leu-Gly-Pro-Ala-Thr- was at the amino terminus of F1. This sequence shows identity at six positions with the hydrophobic amino-terminal sequence of the smaller glycopolypeptide chain, HA2, of the hemagglutinin of influenza virus. Both F1 and HA2 are formed by proteolytic cleavage of precursor glycoproteins (Fo, Sendai virus; HAo, influenza virus). Since these cleavages confer infectivity upon both Sendai and influenza viruses and the ability to induce cell-to-cell fusion upon Sendai virus, the hydrophobic NH2-terminal sequences on F1 and HA2 may play a role in fusion of viral and host-cell membranes.

Amino Acid Sequence↗
PubMed1979

Fusion of L line daughter cells in the presence of Sendai virus.

Sendai virus induces the fusion of daughter cells in a population of murine fibroblasts (L cell line). Mitosis and the ensuing fusion of two daughter cells has been observed by means of time-lapse cinemicrography. The paper documents two types of cell fusion: a) two daughter cells become completely separated at the end of the mitosis, and fuse only after a certain period of time, or b) the daughter cells remain attached through a narrow bridge of cytoplasm which persists between the cells as a consequence of incomplete cytokinesis. Widening of the cytoplasmic bridge ultimately results in the fusion of cells. The interval between the termination of mitosis and the fusion ranged from 45 to 60 min. The biological significance of the resulting polyploid cells is discussed.

Animals↗
PubMed1976

Chromosome-associated paracrystalline nuclear inclusions in the spermatocytes of a pulmonate snail, Planorbarius corneus L.

Chromosome-associated paracrystalloids are regularly found in the spermatocytes of snails which were reared in the laboratory. They seem to be largely specific for the male gametocytes as they have been observed only in few cases in the oocytes. It is likely that paracrystalloids are formed during pachytene at the site of large heterochromatic knobs which originate by fusion of heterochromatic terminal segments of some bivalents. During diplotene they are always connected with the telomeres of three or four bivalents, thus forming a large trefoil-like structure. During metaphase I paracrystalloids are shed off from the chromosomes and transferred to the cytoplasm. In early spermatids they are found again in the nuclei, where they "fade away" during spermiogenesis. Histochemically they consist of basic proteins, which are probably crystallized in the cubic system. Radioactive labeling of the structure could not be achieved, neither by 3H-uridine or thymidine, nor by amino acids. The functional significance of this peculiar structure in unknown. Certain features justify a comparison with synaptonemal polycomplexes.

Animals↗
PubMed1977

Idiopathic chondrolysis of the hip: case report with a review of the literature.

The first case of idiopathic chondrolysis of the hip from South-East Asia is reported, with a review of the literature. The problems of differential diagnosis are discussed. As the condition is rare, it is likely to be misdiagnosed and may well be over-treated. The rarity of the condition and its natural history terminating in spontaneous fusion make it mandatory that a correct preoperative diagnosis be established in order to avoid needless radical surgery. Some of the significant clinicopathological findings are highlighted.

Adult↗
PubMed1979

Quantal division and a postmitotic state in myoblast differentiation.

The reversible arrest of myoblast differentiation by ethidium bromide (EB) has been used to examine the nature of the transition from the proliferative state to terminal differentiation resulting in fusion into muscle fibers. If EB is introduced at the time that myoblasts are shifted to medium that induces fusion, all apparent cytodifferentiation is suspended. When such EB arrested myoblasts are released from EB inhibition they fuse without reentering the cell cycle. If EB arrested myoblasts are released into proliferation promoting medium rather than medium that induces fusion they neither fuse nor proliferate. In this case they remain quiescent in the proliferating medium for an extended period, however, if these myoblasts are subsequently shifted to medium that induces fusion, they fuse without reentering the cell cycle. Apparently the myoblasts have become postmitotic and competent to fuse into muscle fibers during their initial exposure to fusion inducing medium, even though cytodifferentiation has been blocked. Exposure of these postmitotic fusion competent myoblasts to proliferation promoting medium does not stimulate them to reenter the cell cycle but does prevent fusion into muscle fibers. These results are most consistent with a quantal division model of myoblast differentiation rather than a gradual transition from the proliferative state to a state in which fusion occurs.

Animals↗
PubMed1977

Action of brown widow spider venom and botulinum toxin on the frog neuromuscular junction examined with the freeze-fracture technique.

1. Structural changes which normally accompany transmitter release at frog neuromuscular junctions are visualized with the freeze-fracture technique. The effects of brown widow spider venom and botulinum toxin were evaluated in terms of their ability to block or produce these structural changes. Changes produced by these neuropoisons were correlated with their known effects on neurotransmitter release. 3. Fusion of synaptic vesicles with the presynaptic plasmalemma, normally evoked by electrical stimulation, was abolished at neuromuscular junctions from frogs treated with botulinum toxin. 3. The concentration of large intramembranous particles in the presynaptic plasmalemma, an indication of the excess of synaptic vesicle fusion over recovery of synaptic vesicle membrane, was increased by treatment with brown widow spider venom, even in the presence of botulinum toxin. 4. When external calcium was present, sites of vesicle fusion induced by brown widow spider venom, as well as by electrical stimulation, were located mainly in the active zone. In the absence of external calcium, many plasmalemmal deformations, also though to be sites of vesicle fusion, were more evenly dispersed over the presynaptic surface of nerve terminals. 5. Botulinum toxin decreased the number of vesicle fusion sites in the active zone induced by spider venom in the presence of external calcium but had little effect on the number of fusion sites induced by spider venom in the absence of external calcium. 6. Nerve terminals soaked in a sodium-free Ringer solution were partially depleted of vesicles. Addition of spider venom to this Ringer did not cause additional depletion of vesicles. 7. Formation of cation-permeable channels in the presynaptic membrane could account for these effects of spider venom on the frog neuromuscular junction. Botulinum toxin blocks vesicle fusion by some means which is not yet understood.

Animals↗
PubMed1978

Anatomy of bovine mammillitis DNA. I Restriction endonuclease maps of four populations of molecules that differ in the relative orientation of their long and short components.

In this paper, we report that the DNA of bovine mammillitis virus (BMV) consists of two covalently linked components that are 71.5 x 10(6) and 15.7 x 10(6) in molecular weight and designated L and S, respectively. We further report that the BMV DNA consists of four equimolar populations differing only in the orientation of the L and S components relative to each other. This conclusion is based on the following: (i) The sum molecular weight of fragments generated by digestion of BMV DNA with Hsu I, Hpa I, Bgl II, or Xba I significantly exceeds the established molecular weight of the intact DNA. (ii) In each digest, the fragments form three groups differing in molar concentration. In reference to the molar concentration of intact DNA, each enzyme digest contained a set of four fragments 0.25 M in concentration, a set of four fragments 0.5 M in concentration, and a variable size set, unique for each enzyme digest, 1.0 M in concentration. (iii) Experiments involving digestion of intact DNA by lambda exonuclease followed by restriction endonuclease digestion established that each of four 0.5 M fragments were positioned at the termini of the BMV DNA. (iv) Complete maps for the fragments generated by each enzyme established that the 0.25 M fragments arise by fusion of the sequences of the terminal fragments when these are juxtaposed as a consequence of the inversion of L and S components. The maps also established the dimensions of the L and S components. We conclude that the structure of BMV DNA is similar to that of HSV DNA previously shown to consist of two unequal size components that invert relative to each other.

Base Sequence↗
PubMed1977

Morphological and morphometric studies on the ultrastructural changes during the active release of neurosecretory substance from the neurohypophyseal nerve terminals in dehydrated rats.

Secretory nerve terminals in the posterior pituitaries of normal rats and animals dehydrated for 1, 3, 5, 7, and 9 days were observed with the transmission electron microscope. Neurosecretory granules were markedly decreased after dehydration and received the minimum number at 5 days. Small vesicles in the terminals may be classified into two types: one in aggregated vesicles about 53 nm in diameter and the other is dispersed vesicles 66 nm in diameter. The former vesicles are seen in the normal terminals and slightly decreased in number after dehydration, while the latter are hardly seen in normal pituitaries, but increase enormously due to dehydration at 3 days and thereafter. It may be conjectured that the former are the real synaptic vesicles probably containing acetylcholine, while the latter are the fragments of limiting membranes of the neurosecretory granules. Inversely to the slight decrease of dispersed vesicles at 7 and 9 days of dehydration, reticular tubules in the nerve terminals were strikingly increased in volume. Such a terminal reticulum may be formed by fusion of vesicles derived from fragmentation of the envelopes of neurosecretory granules. Finally the reticulum as well as dispersed vesicles may be destroyed by lysosomes.

Animals↗
PubMedDate not supplied

Human haemoglobin genetics.

The genes which direct the structure of human fetal and adult haemoglobin consist of a linked pair of alpha-chain loci on chromosome 16 and the G gamma-A gamma-delta-beta loci complex on chromosome 11. The delta-and beta-chain genes contain inserts similar to those of the mouse and rabbit globin genes. The structure of the various messenger RNAs transcribed from these loci is now worked out although the function of the non-coding regions is not known. The abnormal haemoglobin disorders and thalassaemias result from a variety of lesions at these loci which include single base substitutions, deletions of one or more bases or entire loci, insertions, frame-shifts, fusion genes caused by abnormal crossing over, chain termination mutations and ill-defined defects which lead to a reduced rate of transcription or abnormal structure of messenger RNA. Some progress has been made towards an understanding of the cellular mechanisms whereby the haemoglobin polymorphisms have been maintained. Very little is known about the regulatory mechanisms involved in the switch from fetal to adult haemoglobin production, although it is likely that certain specific areas of the gamma-delta-beta gene complex are involved in its control.

Anemia, Sickle Cell↗
PubMed1979

Telomere replication, kinetochore organizers, and satellite DNA evolution.

Robertsonian rearrangements demonstrate one-break chromosome rearrangement and the reversible appearance and disappearance of telomeres and centromeres. Such events are quite discordant with classical cytogenetic theories, which assume all chromosome rearrangements to require at least two breaks and consider centromeres and telomeres as immutable structures rather than structures determined by mutable DNA sequences. Cytogenetic data from spontaneous and induced telomere-telomere fusions in mammals support a molecular model of terminal DNA synthesis in which all telomeres are similar and recombine before replication and subsequent separation. This, along with evidence for a hypothetical DNA sequence, the kinetochore organizer, readily explains latent telomeres, latent centromeres, and reversible (one-break) Robertsonian rearrangements. A second model, involving simply recombination between like satellite DNA sequences on different chromosomes, explains not only how one satellite can simultaneously evolve on different chromosomes, but also why satellite DNA is usually located near centromeres or telomeres and why it maintains a preferred orientation with respect to the centromere.

Base Sequence↗
PubMed1979

Sites within gene lacZ of Escherichia coli for formation of active hybrid beta-galactosidase molecules.

We describe the genetic analysis of 21 Escherichia coli strains in which the amino-terminal sequence of beta-galactosidase has been removed and replaced by an amino-terminal sequence from one or another of the proteins involved in maltose transport. Genetic mapping of the lacZ end of these fused genes indicates that only those fusions in which fewer than 41 amino acids are removed from the amino-terminal sequence of beta-galactosidase result in enzymatically active molecules. Within the region between amino acid 17 and amino acid 41 there are at least four or five sites where enzymatically active hybrid proteins can be formed.

Amino Acid Sequence↗
PubMed1978

Hemoglobin Lincoln Park: a betadelta fusion (anti-Lepore) variant with an amino acid deletion in the delta chain-derived segment.

An electrophoretically slow-moving hemoglobin variant was identified in three members of a family originating from Southern Mexico. The variant, Hb Lincoln Park, made up approximately 14% of the total hemoglobin and appeared to have normal stability and functional properties. None of the individuals in whom the abnormal hemoglobin was present was anemic, but each had a mildly elevated reticulocyte count. Structural data suggest that the non-alpha chain of Hb Lincoln Park represents a betadelta gene-fusion product, with normal beta chain structure of the amino-terminal portion of the chain and delta sequences subsequently, the crossover point occurring between animo acid residues 22 and 50. An additional abnormality is the deletion of valine-137, a component of the delta gene-derived segment of the betadelta chain. To account for the development of this abnormal globin chain, a series of intergenic crossovers is proposed; the first, a nonhomologous crossover between the beta and delta genes, presumably gave rise to the betadelta fusion gene; two additional crossovers, one of them unequal, may then have occurred between the same beta and delta genes to produce the amino acid deletion.

Adult↗