Characterization of HKE2: an ancient antigen encoded in the major histocompatibility complex.

Genes at the centromeric end of the human leukocyte antigen region influence adaptive autoimmune diseases and cancer. In this study, we characterized protein expression of HKE2, a gene located in the centromeric portion of the class II region of the major histocompatibility complex encoding subunit 6 of prefoldin. Immunohistochemical analysis using an anti-HKE2 antibody indicated that HKE2 protein expression is dramatically upregulated as a consequence of activation. In a tissue microarray and in several tumors, HKE2 was overexpressed in certain cancers compared with normal counterparts. The localization of the HKE2 gene to the class II region, its cytoplasmic expression and putative protein-binding domain suggest that HKE2 may function in adaptive immunity and cancer.

1,2-Bis(2-pyridylethynyl)benzene, a novel trans-chelating bipyridyl ligand. structural characterization of the complexes with silver(I) triflate and palladium(II) chloride.

The design, synthesis, and complexation characteristics of the bipyridyl ligand 1,2-bis-(2-pyridylethynyl)benzene are described. The X-ray crystallographic characterization of the 1:1 complexes of 1,2-bis(2-pyridylethynyl)benzene with silver(I) triflate and palladium(II) chloride are described. In the X-ray crystal structure of the silver(I) triflate complex the ligand is essentially planar with negligible distortion compatible with a good fit of the cation in the "cavity" between the pyridine N atoms. Indeed the silver center is almost linear with the N(1)-Ag(1)-N(2) angle of 177.02(10) degrees. The ligand is also essentially planar in the palladium(II) chloride complex with square planar coordination about the palladium with the N(1)-Pd(1)-N(2), Cl(2)-Pd(1)-Cl(2), and N(1)-Pd(1)-Cl(2) angles at 179.53(7), 177.17(2), and 90.52(5) degrees, respectively.

3-amino-1,2,4-benzotriazine 4-oxide: characterization of a new metabolite arising from bioreductive processing of the antitumor agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine).

Tirapazamine (1) is a promising antitumor agent that selectively causes DNA damage in hypoxic tumor cells, following one-electron bioreductive activation. Surprisingly, after more than 10 years of study, the products arising from bioreductive metabolism of tirapazamine have not been completely characterized. The two previously characterized metabolites are 3-amino-1,2,4-benzotriazine 1-oxide (3) and 3-amino-1,2,4-benzotriazine (5). In this work, 3-amino-1,2,4-benzotriazine 4-oxide (4) is identified for the first time as a product resulting from one-electron activation of the antitumor agent tirapazamine by the enzymes xanthine/xanthine oxidase and NADPH:cytochrome P450 oxidoreductase. As part of this work, the novel N-oxide (4) was unambiguously synthesized and characterized using NMR spectroscopy, UV-vis spectroscopy, LC/MS, and X-ray crystallography. Under conditions where the parent drug tirapazamine is enzymatically activated, the metabolite 4 is produced but readily undergoes further reduction to the benzotriazine (5). Thus, under circumstances where extensive reductive metabolism occurs, the yield of the 4-oxide (4) decreases. In contrast, the isomeric two-electron reduction product 3-amino-1,2,4-benzotriazine 1-oxide (3) does not readily undergo enzymatic reduction and, therefore, is found as a major bioreductive metabolite under all conditions. Finally, the ability of the 4-oxide metabolite (4) to participate in tirapazamine-mediated DNA damage is considered.

Development of novel water-soluble, organometallic compounds for potential use in nuclear medicine: synthesis, characterization, and (1)H and (31)P NMR investigations of the complexes fac-[ReBr(CO)3L] (L=bis(bis(hydroxymethyl)phosphino)ethane, bis(bis(hydroxymethyl)phosphino)benzene).

The bidentate, water-soluble phosphine ligands, bis(bis(hydroxymethyl)phosphino)benzene (HMPB, 1) and bis(bis(hydroxymethyl)phosphino)ethane (HMPE, 2) were reacted with the organometallic precursor fac-[ReBr(3)(CO)(3)](2-), 3, to produce the complexes fac-[Re(OH(2))(CO)(3)L](+) and fac-[ReBr(CO)(3)L] (L = HMPE, HMPB), respectively, in good yields. The rhenium complexes fac-[ReBr(CO)(3)HMPB], 5, and fac-[ ReBr(CO)(3)HMPE], 8, were characterized using (1)H and (31)P NMR spectroscopy. The structure of fac-[ReBr(CO)(3)HMPB] was confirmed by single-crystal X-ray spectroscopy. The substitution reactions of HMPE/HMPB with the rhenium precursor 3 in aqueous solution were monitored using time-dependent (31)P NMR techniques. A significant discrepancy in the reaction kinetics and the substitution mechanism between the two bidentate ligands could be observed presumably due to the different chemical backbones.

Donor-acceptor interactions in crystal engineering.

The molecular complex formed between 4-methyltolane and bis(4-N-methylpyridinium)ethyne ditriflate is reported. The X-ray crystal structure indicates that the crystalline superstructure consists of infinite zigzag ribbons of interlocked donor-acceptor complexes separated by triflate counterions.

Novel terpenoids from the West Indian sea whip Pseudopterogorgia elisabethae (Bayer). Elisapterosins A and B: rearranged diterpenes possessing an unprecedented cagelike framework.

Four diterpenes and a nor-diterpenoid, all of which possess unusual carbocyclic skeletons, were isolated from the hexane solubles of the West Indian gorgonian Pseudopterogorgia elisabethae. The structures and relative configurations of novel metabolites elisabethin D (2), elisabethin D acetate (3), 3-epi-elisabanolide (5), elisapterosin A (6), and elisapterosin B (7) were elucidated by interpretation of overall spectral data, which included 2D NMR correlation methods, IR, UV, and accurate mass measurements (HREI-MS and HRFAB-MS), chemical reactions, and X-ray diffraction analyses. The tetracyclic carbon skeleton of the elisapterosins is undescribed and constitutes a new class of C(20) rearranged diterpenes. Elisapterosin B displays strong in vitro anti-tuberculosis activity.

Unusual folded conformation of nicotinamide adenine dinucleotide bound to flavin reductase P.

The 2.1 A resolution crystal structure of flavin reductase P with the inhibitor nicotinamide adenine dinucleotide (NAD) bound in the active site has been determined. NAD adopts a novel, folded conformation in which the nicotinamide and adenine rings stack in parallel with an inter-ring distance of 3.6 A. The pyrophosphate binds next to the flavin cofactor isoalloxazine, while the stacked nicotinamide/adenine moiety faces away from the flavin. The observed NAD conformation is quite different from the extended conformations observed in other enzyme/NAD(P) structures; however, it resembles the conformation proposed for NAD in solution. The flavin reductase P/NAD structure provides new information about the conformational diversity of NAD, which is important for understanding catalysis. This structure offers the first crystallographic evidence of a folded NAD with ring stacking, and it is the first enzyme structure containing an FMN cofactor interacting with NAD(P). Analysis of the structure suggests a possible dynamic mechanism underlying NADPH substrate specificity and product release that involves unfolding and folding of NADP(H).

1-(1,3-Benzothiazol-2-yl)-2-(2-bromo-5-nitrophenyl)ethanone.

The title compound, C15H9BrN2O3S, was isolated as an unexpected product from the reaction of the anion of sodium 2-(1,3-benzothiazolyl)ethanonitrile with alpha,2-dibromo-5-nitrotoluene. Its structure features a benzothiazole fragment and a bromo- and nitro-substituted phenyl ring linked by a methyl ketone group. The dihedral angle between the benzothiazole and phenyl rings is 103.7 (2) degrees. The benzothiazole fragment is planar, with a maximum deviation of 0.021 (2) A. The nitro group is slightly rotated out of the phenyl-ring plane, with a O(2)-N(2)-C(14)-C(15) torsion angle of 16.4(7) degrees.

Calyxamines A and B, novel piperidine alkaloids from the Caribbean sea sponge Calyx podatypa.

Calyxamines A (1) and B (2) are 2,2,4,6,6-pentasubstituted piperidine alkaloids possessing novel carbon skeletons isolated from the marine sponge Calyx podatypa collected in Puerto Rico. Their structures, after derivatization with trifluoroacetic acid, have been determined by a combination of X-ray and spectroscopic methods. A plausible biogenetic pathway to the calyxamines is suggested.

Age as a prognostic factor in open tibial fractures in children.

Thirty-one consecutive open fractures of the tibia were reviewed prospectively. Duration from injury until last examination averaged 3.7 years. The patients were divided into 2 groups for comparison: Group A consisted of children younger than 12 years of age and Group B of patients 12 years of age or older. The fractures were graded according to the system of Gustilo and Anderson. The severity of patient injuries in each group was similar. The treatments were likewise similar, but for all parameters studied, the younger patients fared better than their older counterparts. This study suggests that open fractures in children younger than 12 years of age require less aggressive surgical treatment, heal faster, are more resistant to infection, and have fewer complications than those in older children.

Preliminary X-ray diffraction studies of an RNA pseudoknot that inhibits HIV-1 reverse transcriptase.

Crystals of a 26-nucleotide pseudoknot RNA, PK26, have been grown. The RNA was produced using phosphoramidite chemistry and was purified by denaturing polyacrylamide electrophoresis. The crystallization was robust with respect to changes in the number of nucleotides and to the salt used as precipitant. The crystals belong to space group P4(1)22 or P4(3)22 with unit-cell dimensions a = b = 61.6, c = 98.9 A. The best crystals diffract X-rays to 2.9 A. Three different sequences incorporating a single 5-bromo-deoxyuridine or 5-bromo-uridine nucleotide were also crystallized. Two of these derivatives are being used to determine the structure by multiple isomorphous replacement.

The structure of an RNA dodecamer shows how tandem U-U base pairs increase the range of stable RNA structures and the diversity of recognition sites.

BACKGROUND: Non-canonical base pairs are fundamental building blocks of RNA structures. They can adopt geometries quite different from those of canonical base pairs and are common in RNA molecules that do not transfer sequence information. Tandem U-U base pairs occur frequently, and can stabilize duplex formation despite the fact that a single U-U base pair is destabilizing. RESULTS: We determined the crystal structure of the RNA dodecamer GGCGCUUGCGUC at 2.4 A resolution. The molecule forms a duplex containing tandem U-U base pairs, which introduce an overall bend of 11-12 degrees in the duplex resulting from conformational changes at each interface between the tandem U-U base pairs and a flanking duplex sequence. The formation of the U-U base pairs cause small changes in several backbone torsion angles; base stacking is preserved and two hydrogen bonds are formed per base pair, explaining the stability of the structure. CONCLUSIONS: Tandem U-U base pairs can produce stable structures not accessible to normal A-form RNA, which may allow the formation of specific interfaces for RNA-RNA or RNA-protein recognition. These base-pairs show an unusual pattern of hydrogen-bond donors and acceptors in the major and minor grooves, which could also act as a recognition site.