Neil R. Thomas

Mutation in myosin heavy chain 6 causes atrial septal defect.

Atrial septal defect is one of the most common forms of congenital heart malformation. We identified a new locus linked with atrial septal defect on chromosome 14q12 in a large family with dominantly inherited atrial septal defect. The underlying mutation is a missense substitution, I820N, in α-myosin heavy chain (MYH6), a structural protein expressed at high levels in the developing atria, which affects the binding of the heavy chain to its regulatory light chain. The cardiac transcription factor TBX5 strongly regulates expression of MYH6, but mutant forms of TBX5, which cause Holt-Oram syndrome, do not. Morpholino knock-down of expression of the chick MYH6 homolog eliminates the formation of the atrial septum without overtly affecting atrial chamber formation. These data provide evidence for a link between a transcription factor, a structural protein and congenital heart disease.

Temperature dependence of the photoluminescence emission from thiol-capped PbS quantum dots

The authors report the temperature dependence of the near-infrared photoluminescence (PL) emission from thiol-capped PbS quantum dots. The high thermal stability of the PL allows the authors to study the thermal broadening of the dot emission over an extended temperature range (4–300K). The authors show that the linewidth of the dot PL emission is strongly enhanced at temperatures above 150K. This behavior is attributed to dephasing of the quantum electronic states by carrier interaction with longitudinal optical phonons. The authors’ data also indicate that the strength of the carrier-phonon coupling is larger in smaller dots.

Continuous kinetic resolution catalysed by cross-linked enzyme aggregates, ‘CLEAs’, in supercritical CO2

We report the use of cross-linked enzyme aggregates (CLEAs®) to catalyse the kinetic resolution of tetralol and 1-phenylethanol in a continuous supercritical carbon dioxide (scCO2) system. We describe the performance of the CLEA from Candida antarctica lipase B (CALB) and compare this to the catalytic activity of Novozym 435 (CALB immobilised on a macroporous acrylic resin). In addition, we report a two-stage reaction with the kinetic resolution of 1-phenylethanol performed in series with the metal (Pd) catalysed hydrogenation of acetophenone. Reactions performed in series have a potential economic advantage as the second, and subsequent reactions do not require additional expenditure of energy for re-pressurization of solvent.

Polyhydroxylated azepanes as new motifs for DNA minor groove binding agents.

The synthesis of 1,3-bis-[3,4,5,6-tetrahydroxyazepane-N-p-phenoxy] and 1,3-bis-[3,4,5,6-tetrahydroxyazepane-N-p-benzyloxy] propanes is reported. These compounds have been prepared to investigate the potential of incorporating iminosugars as useful recognition elements in DNA minor groove binding agents. The compounds were shown to have very moderate binding affinities for DNA in thermal denaturation and ethidium bromide displacement assays when compared with propamidine. They were also found to possess some in vitro anticancer activity that did not correlate with their DNA binding affinity.

Synthesis and biological evaluation of new inhibitors of UDP-Galf transferase--a key enzyme in M. tuberculosis cell wall biosynthesis.

Two iminosugars have been designed and synthesized as potential inhibitors of UDP-Galf transferase, an enzyme involved in Mycobacterium tuberculosis cell wall biosynthesis. The design is based on a proposed model of the transition state for the transferase reaction. One of the two racemic compounds is the first reported inhibitor of the target enzyme from M. smegmatis.

Hapten design for the generation of catalytic antibodies

This article brings together all of the kinetic data on catalytic antibodies available in the published literature at the time of writing (September, 1993). The data have been presented so that they can be analyzed for any significant trends that arise from relating the structure of the transition-state analog/hapten to the type and efficiency of the catalytic antibody activity elicited.

The Biocompatibility of Apoferritin‐Encapsulated PbS Quantum Dots

The biocompatibility of a nanocomposite based on a Pbs quantum dots (QD) entrapped in the hollow core of an apoferritin protein cage is examined. This offers a water-soluble hybrid construct with stable and tunable fluorescence emission at wavelengths larger than 1000nm. Native polyacrylamide gel-electrophoresis studies show that the PbS QDs do not alter the external surface of apoferritin or its migratory behavior. Apoferritin is obtained from ferritin molecules by reductive dissolution of its iron oxide core. MTT assays were performed on normal and cancer cell lines and recorded the cell viability after treatment with AFt-PbS at different concentrations and up to 72-hour. Cells were cultured under optimum conditions in RPMI nutrient medium supplemented with 10 fetal bovine serum, and subcultivated twice weekly to maintain logarithmic growth. Cells were seeded into 96-well microtiter plates at a density of 5 A� 103 per well and allowed 24-hour to adhere before AFt, PbS QDs and AFt-PbS composites were introduced with final concentrations of QDs.

Chemoenzymatic Synthesis, Inhibition Studies, and X-ray Crystallographic Analysis of the Phosphono Analog of UDP-Galp as an Inhibitor and Mechanistic Probe for UDP-Galactopyranose Mutase

UDP (uridine diphosphate) galactopyranose mutase (UGM) is involved in the cell wall biosynthesis of many pathogenic microorganisms. UGM catalyzes the reversible conversion of UDP-α-D-galactopyranose into UDP-α-D-galactofuranose, with the latter being the precursor of galactofuranose (Galf) residues in cell walls. Glycoconjugates of Galf are essential components in the cell wall of various pathogenic bacteria, including Mycobacterium tuberculosis, the causative agent of tuberculosis. The absence of Galf in humans and its bacterial requirement make UGM a potential target for developing novel antibacterial agents. In this article, we report the synthesis, inhibitory activity, and X-ray crystallographic studies of UDP-phosphono-galactopyranose, a nonhydrolyzable C-glycosidic phosphonate. This is the first report on the synthesis of a phosphonate analog of UDP-α-D-galactopyranose by a chemoenzymatic phosphoryl coupling method. The phosphonate was evaluated against three bacterial UGMs and showed only moderate inhibition. We determined the crystal structure of the phosphonate analog bound to Deinococcus radiodurans UGM at 2.6 Å resolution. The phosphonate analog is bound in a novel conformation not observed in UGM-substrate complex structures or in other enzyme-sugar nucleotide phosphonate complexes. This complex structure provides a structural basis for the observed micromolar inhibition towards UGM. Steric clashes, loss of electrostatic stabilization between an active-site arginine (Arg305) and the phosphonate analog, and a 180° flip of the hexose moiety account for the differences in the binding orientations of the isosteric phosphonate analog and the physiological substrate. This provides new insight into the ability of a sugar-nucleotide-binding enzyme to orient a substrate analog in an unexpected geometry and should be taken into consideration in designing such enzyme inhibitors.

Tailoring the physical properties of thiol-capped PbS quantum dots by thermal annealing.

We show that the thermal annealing of thiol-capped PbS colloidal quantum dots provides a means of narrowing the nanoparticle size distribution, increasing the size of the quantum dots and facilitating their coalescence preferentially along the 100 crystallographic axes. We exploit these phenomena to tune the photoluminescence emission of an ensemble of dots and to narrow the optical linewidth to values that compare with those reported at room temperature for single PbS quantum dots. We probe the influence of annealing on the electronic properties of the quantum dots by temperature dependent studies of the photoluminescence and magneto-photoluminescence.

Crystal structure of the antimicrobial peptidase lysostaphin from Staphylococcus simulans

Staphylococcus simulans biovar staphylolyticus lysostaphin efficiently cleaves Staphylococcus aureus cell walls. The protein is in late clinical trials as a topical anti‐staphylococcal agent, and can be used to prevent staphylococcal growth on artificial surfaces. Moreover, the gene has been both stably engineered into and virally delivered to mice or livestock to obtain resistance against staphylococci. Here, we report the first crystal structure of mature lysostaphin and two structures of its isolated catalytic domain at 3.5, 1.78 and 1.26 Å resolution, respectively. The structure of the mature active enzyme confirms its expected organization into catalytic and cell‐wall‐targeting domains. It also indicates that the domains are mobile with respect to each other because of the presence of a highly flexible peptide linker. The high‐resolution structures of the catalytic domain provide details of Zn2+ coordination and may serve as a starting point for the engineering of lysostaphin variants with improved biotechnological characteristics.