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At least 1,189 records · Page 66Linked to original sources
PubMed1984

[Morphogenetic role of the cortical cytoskeleton and plasma membrane of the ovum].

The classical embryological conception of egg cortex localization of morphogenetic determinants is interpreted in terms of current data on cell cortex and cell surface organization. The egg surface complex that involves cortical cytoskeleton--oolemma (stabilized with transmembrane linkage between the cytoskeleton and ligands of egg envelope extracellular matrix) presumably ensures storage of cortical morphogenetic information, i.e. the spatial memory of egg and zygote as a heterogeneous distribution of membrane and cortex components. Any of the rigid cortical complex component--membrane receptors, structural cytoskeletal proteins and also embedded in cortical gel-like framework of actin filaments RNP's and non-structural proteins (e.g. enzymes) may function as possible morphogenetic determinants. The coupling of general cortical rigidity and local contractility during the cleavage may be accounted (after Condeelis, 1981) for the actin-myosin interaction following a local dissociation of the stiff structural complex of actin--actin-binding proteins.

Actins↗
PubMed1981

[Reflection of the periodic structure of complex acoustic signals in the summated activity of inferior colliculus neurons in cats].

The frequency following response (FFR) of the cat posterior colliculus rather roughly reflects the subtle temporal and spectral properties of complex tonal and speech signals. The FFR relation to a certain phase of the complex signal depends on the signal's main frequency and phase spectrum. The FFR periodicity corresponds to the signal's base frequency even if it is missing from the spectrum. A complex signal with an missing base frequency can induce a periodic SSR even if the frequency itself is not able to induce the FFR. The data obtained characterize some neurophysiological mechanisms of perception of complex sound signal's periodicity.

Acoustic Stimulation↗
PubMed1977

[The construction of models intending spatial representation of complex vessel structures demonstrated by means of the mammalian glomerulus].

This report presents information about a method to construct a wax-sheet model of rat and human glomerula, able to be divided into several segments. Based on the wax model consisting of segments a glomerula model is developed, showing the axis of the glomerula capillaries formed by an ironwire. By means of this model it will be possible to follow the course of the capillaries precisely.

Animals↗
PubMedDate not supplied

[Modification of the DNA spatial structure when complexed with cisplatin].

The experimental and theoretical analyses of the conformational transitions of DNA-cis-platinum complexes have been carried out. It is shown that at low concentrations of the ligand, the thermodynamic parameters of the helix-coil transition of the complexes are not the result of the local B-->A transition.

Animals↗
PubMed2004

RNA polymerase II structure: from core to functional complexes.

New structural studies of RNA polymerase II (Pol II) complexes mark the beginning of a detailed mechanistic analysis of the eukaryotic mRNA transcription cycle. Crystallographic models of the complete Pol II, together with new biochemical and electron microscopic data, give insights into transcription initiation. The first X-ray analysis of a Pol II complex with a transcription factor, the elongation factor TFIIS, supports the idea that the polymerase has a 'tunable' active site that switches between mRNA synthesis and cleavage. The new studies also show that domains of transcription factors can enter polymerase openings, to modulate function during transcription.

Protein Structure, Tertiary↗
PubMed2004

Inhibition of Leishmania major pteridine reductase by 2,4,6-triaminoquinazoline: structure of the NADPH ternary complex.

The structure of Leishmania major pteridine reductase (PTR1) in complex with NADPH and the inhibitor 2,4,6-triaminoquinazoline (TAQ) has been solved in a new crystal form by molecular replacement and refined to 2.6 A resolution. The inhibitor mimics a fragment, the pterin head group, of the archetypal antifolate drug methotrexate (MTX) and exploits similar chemical features to bind in the PTR1 active site. Despite being a much smaller molecule, TAQ displays a similar inhibition constant to that of MTX. PTR1 is a target for the development of improved therapies for infections caused by trypanosomatid parasites and this analysis provides information to assist the structure-based development of novel enzyme inhibitors.

Animals↗
PubMed2000

Mechanism of catalysis of the cofactor-independent phosphoglycerate mutase from Bacillus stearothermophilus. Crystal structure of the complex with 2-phosphoglycerate.

The structure of the complex between the 2, 3-diphosphoglycerate-independent phosphoglycerate mutase (iPGM) from Bacillus stearothermophilus and its 3-phosphoglycerate substrate has recently been solved, and analysis of this structure allowed formulation of a mechanism for iPGM catalysis. In order to obtain further evidence for this mechanism, we have solved the structure of this iPGM complexed with 2-phosphoglycerate and two Mn(2+) ions at 1. 7-A resolution. The structure consists of two different domains connected by two loops and interacting through a network of hydrogen bonds. This structure is consistent with the proposed mechanism for iPGM catalysis, with the two main steps in catalysis being a phosphatase reaction removing the phosphate from 2- or 3-phosphoglycerate, generating an enzyme-bound phosphoserine intermediate, followed by a phosphotransferase reaction as the phosphate is transferred from the enzyme back to the glycerate moiety. The structure also allowed the assignment of the function of the two domains of the enzyme, one of which participates in the phosphatase reaction and formation of the phosphoserine enzyme intermediate, with the other involved in the phosphotransferase reaction regenerating phosphoglycerate. Significant structural similarity has also been found between the active site of the iPGM domain catalyzing the phosphatase reaction and Escherichia coli alkaline phosphatase.

Amino Acid Sequence↗
PubMed1987

Multiple synaptonemal complexes (polycomplexes): origin, structure and function.

Multiple synaptonemal complexes (polycomplexes) (PC) are similar in structure to synaptonemal complexes (SC) and are also highly conserved through evolution. They have been described in over 70 organisms throughout all life forms. The appearance of PCs are restricted to meiotic and germ-line derived tissues and are most commonly present after SC formation. However, in a number of animals and plants, both extra- and intranuclear PCs are present during premeiotic and pre-pachytene stages. The structure and biochemical composition of PCs is similar to SCs that the basic unit is tripartite, consisting of two lateral elements and a central region (in which transverse elements are located), and the dimensions of such structures are equivalent. Stacking of SC subunits, while still maintaining equivalent SC dimensions, creates a problem since the lateral elements (LE) would then be twice as thick in the PC as compared to the SC. Recently, it has been shown that the LE of the SC is actually multistranded, thus the LE of each subunit of the PC is half as thick as its counterpart in the SC.

Animals↗
PubMed2006

Unprecedented alkene complex of zinc(II): structures and bonding of divinylzinc complexes.

This report describes the solid-state structures of a series of divinylzinc complexes, one of which represents the only structurally characterized zinc(II) pi-complex. Vinylzinc reagents, Zn[C(Me)=CH2]2 (1) and Zn[C(H)=CMe2]2 (2), have been synthesized and isolated as white crystalline solids in 66 and 72% yield, respectively. Each compound exhibits an infinite polymeric architecture in the solid state via a series of zinc-pi (1) and zinc-sigma-bonded (2) bridging interactions. Addition of chelating ligands to these divinylzinc compounds allowed isolation of the monomeric adducts (bipy)Zn[C(Me)=CH2]2 (1.bipy), (tmeda)Zn[C(Me)=CH2]2 (1*tmeda), (bipy)Zn[C(H)=CMe2]2 (2*bipy), and (tmeda)Zn[C(H)=CMe2]2 (2*tmeda), of which 1*bipy, 2*bipy, and 2*tmeda have been characterized crystallographically.

Alkenes↗
PubMed2003

Crystal structure of the MurG:UDP-GlcNAc complex reveals common structural principles of a superfamily of glycosyltransferases.

MurG is an essential glycosyltransferase that forms the glycosidic linkage between N-acetyl muramyl pentapeptide and N-acetyl glucosamine in the biosynthesis of the bacterial cell wall. This enzyme is a member of a major superfamily of NDP-glycosyltransferases for which no x-ray structures containing intact substrates have been reported. Here we present the 2.5-A crystal structure of Escherichia coli MurG in complex with its donor substrate, UDP-GlcNAc. Combined with genomic analysis of other superfamily members and site-specific mutagenesis of E. coli MurG, this structure sheds light on the molecular basis for both donor and acceptor selectivity for the superfamily. This structural analysis suggests that it will be possible to evolve new glycosyltransferases from prototypical superfamily members by varying two key loops while maintaining the overall architecture of the family and preserving key residues.

Amino Acid Sequence↗
PubMed2006

Apparently complex high-pressure phase of gallium as a simple modulated structure.

The phase of gallium GaII, with symmetry C222(1) and 104 atoms per unit cell, has been recently reported as an example of structural complexity under high pressure. It is shown here that this phase is a simple modulated distortion of an average structure of Fddd symmetry with all atoms structurally equivalent. The modulation can be described with only 4 parameters and satisfies symmetry properties described by a centrosymmetric superspace group. The structural distortion is dominated by a frozen transversal mode associated with a single irreducible representation of Fddd, with a wave vector on the line Q, at an edge of the Brillouin zone. The average structure can be related with an hcp configuration through simple sliding of hcp layers, reminiscent of the hcp-bcc Bürgers mechanism.

Journal Article↗