Puckering behavior in six new phosphoric triamides containing aliphatic six- and seven-membered ring groups and a database survey of analogous ring-containing structures

The influence of a N heteroatom on the ring conformations of six- and seven- membered aliphatic rings in six new C(O)NHP(O)-based phosphoric triamide structures (analysed by X-ray crystallography) is investigated. Additionally the influence of steric and crystal packing effects is also studied by the analysis of Hirshfeld surfaces. The results are compared to analogous structures with three- to seven- aliphatic membered rings deposited in the Cambridge Structural Database. In the newly determined structures, the six-membered rings only show the near-chair conformation with a maximum deviation of the θ puckering parameter of 4.4° from the ideal chair value of 0°/180°, while the seven-membered rings are found in different conformations such as near-chair, twist chair and twist sofa

Analysis of C3 Suggests Three Periods of Positive Selection Events and Different Evolutionary Patterns between Fish and Mammals

BACKGROUND: The third complement component (C3) is a central protein of the complement system conserved from fish to mammals. It also showed distinct characteristics in different animal groups. Striking features of the fish complement system were unveiled, including prominent levels of extrahepatic expression and isotypic diversity of the complement components. The evidences of the involvement of complement system in the enhancement of B and T cell responses found in mammals indicated that the complement system also serves as a bridge between the innate and adaptive responses. For the reasons mentioned above, it is interesting to explore the evolutionary process of C3 genes and to investigate whether the huge differences between aquatic and terrestrial environments affected the C3 evolution between fish and mammals. METHODOLOGY/PRINCIPAL FINDINGS: Analysis revealed that these two groups of animals had experienced different evolution patterns. The mammalian C3 genes were under purifying selection pressure while the positive selection pressure was detected in fish C3 genes. Three periods of positive selection events of C3 genes were also detected. Two happened on the ancestral lineages to all vertebrates and mammals, respectively, one happened on early period of fish evolutionary history. CONCLUSIONS/SIGNIFICANCE: Three periods of positive selection events had happened on C3 genes during history and the fish and mammals C3 genes experience different evolutionary patterns for their distinct living environments

2-(exo-Tricyclo[5.2.1.0<SUP>2,6</SUP>]deca-4,8-dien-3-endo-yl)acetaldehyde 2,4-dinitrophenylhydrazone

The six-membered ring of the norbornene moiety in the title compound, C18H18N4O4, is in a slightly distorted boat conformation, and the two five-membered rings within it adopt envelope conformations. The structure is stabilized by inter- and intramolecular N-H⋯O hydrogen bonds

Crystal and Molecular Structure of Desmodin

The crystal structure of the title compound has been determined from X-ray diffraction. The compound crystallizes from benzene in the orthorhombic system, space group P212121, with unit cell parameters: a = 8.485(2), b = 9.816(2), c = 22.597(4) A, Z = 4, V = 1881.9(7) A3. The structure was determined by direct methods and refined to a final R-factor of 0.04. Six membered rings B and E are planar. Ring A and ring C are in slightly distorted sofa conformation. Ring D is in envelope conformation. The structure is stabilised by weak intermolecular C-H...O hydrogen bond

4-tert-Butyl-2,6-bis(piperidinomethyl)phenol

The title compound, $C_{22}H_{36}N_2O$, contains piperidine as a major constituent. The two piperidine rings attached to the phenyl ring are in chair conformations. The structure is stabilized by van der Waals forces as well as $O-H^{...}N$ intramolecular hydrogen bonds

Tricoccin R6

The X-ray crystal structure of the title compound, $(C_{25}H_{28}O_8)$, has been determined. In the structure, both the terminal five-membered rings (A and F) are planar. The fused five-membered rings C and E are in envelope conformations, and ring B is in a slightly distorted half-chair conformation. The six-membered ring D is in a slightly distorted sofa conformation. The structure is stabilized by $O-H^{...}O$ hydrogen bonds and $C-H^{...}O$ inter- and intramolecular interactions

A disulfide-bond cascade mechanism for arsenic(III) S-adenosylmethionine methyltransferase

Methylation of the toxic metalloid arsenic is widespread in nature. Members of every kingdom have arsenic(III) S-adenosylmethionine (SAM) methyltransferase enzymes, which are termed ArsM in microbes and AS3MT in animals, including humans. Trivalent arsenic(III) is methylated up to three times to form methylarsenite [MAs(III)], dimethylarsenite [DMAs(III)] and the volatile trimethylarsine [TMAs(III)]. In microbes, arsenic methylation is a detoxification process. In humans, MAs(III) and DMAs(III) are more toxic and carcinogenic than either inorganic arsenate or arsenite. Here, new crystal structures are reported of ArsM from the thermophilic eukaryotic alga Cyanidioschyzon sp. 5508 (CmArsM) with the bound aromatic arsenicals phenylarsenite [PhAs(III)] at 1.80 Å resolution and reduced roxarsone [Rox(III)] at 2.25 Å resolution. These organoarsenicals are bound to two of four conserved cysteine residues: Cys174 and Cys224. The electron density extends the structure to include a newly identified conserved cysteine residue, Cys44, which is disulfide-bonded to the fourth conserved cysteine residue, Cys72. A second disulfide bond between Cys72 and Cys174 had been observed previously in a structure with bound SAM. The loop containing Cys44 and Cys72 shifts by nearly 6.5 Å in the arsenic(III)-bound structures compared with the SAM-bound structure, which suggests that this movement leads to formation of the Cys72-Cys174 disulfide bond. A model is proposed for the catalytic mechanism of arsenic(III) SAM methyltransferases in which a disulfide-bond cascade maintains the products in the trivalent state

Structure of an As(III) <i>S</i>-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation

Enzymatic methylation of arsenic is a detoxification process in microorganisms but in humans may activate the metalloid to more carcinogenic species. We describe the first structure of an As­(III) <i>S</i>-adenosylmethionine methyltransferase by X-ray crystallography that reveals a novel As­(III) binding domain. The structure of the methyltransferase from the thermophilic eukaryotic alga <i>Cyanidioschyzon merolae</i> reveals the relationship between the arsenic and <i>S</i>-adenosylmethionine binding sites to a final resolution of ∼1.6 Å. As­(III) binding causes little change in conformation, but binding of SAM reorients helix α4 and a loop (residues 49–80) toward the As­(III) binding domain, positioning the methyl group for transfer to the metalloid. There is no evidence of a reductase domain. These results are consistent with previous suggestions that arsenic remains trivalent during the catalytic cycle. A homology model of human As­(III) <i>S</i>-adenosylmethionine methyltransferase with the location of known polymorphisms was constructed. The structure provides insights into the mechanism of substrate binding and catalysis

Structure of an As(III) <i>S</i>-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation

Enzymatic methylation of arsenic is a detoxification process in microorganisms but in humans may activate the metalloid to more carcinogenic species. We describe the first structure of an As­(III) <i>S</i>-adenosylmethionine methyltransferase by X-ray crystallography that reveals a novel As­(III) binding domain. The structure of the methyltransferase from the thermophilic eukaryotic alga <i>Cyanidioschyzon merolae</i> reveals the relationship between the arsenic and <i>S</i>-adenosylmethionine binding sites to a final resolution of ∼1.6 Å. As­(III) binding causes little change in conformation, but binding of SAM reorients helix α4 and a loop (residues 49–80) toward the As­(III) binding domain, positioning the methyl group for transfer to the metalloid. There is no evidence of a reductase domain. These results are consistent with previous suggestions that arsenic remains trivalent during the catalytic cycle. A homology model of human As­(III) <i>S</i>-adenosylmethionine methyltransferase with the location of known polymorphisms was constructed. The structure provides insights into the mechanism of substrate binding and catalysis