58,566 research outputs found
Mapping class groups and outer automorphism groups of free groups are C*-simple
We prove that the reduced C*-algebras of centerless mapping class groups and
outer automorphism groups of free groups are simple, as are the irreducible
pure subgroups of mapping class groups and the analogous subgroups of outer
automorphism groups of free groups.Comment: 10 pages, amstex. J. Functional Analysis, to be publishe
In silico prediction of mutant HIV-1 proteases cleaving a target sequence
HIV-1 protease represents an appealing system for directed enzyme re-design,
since it has various different endogenous targets, a relatively simple
structure and it is well studied. Recently Chaudhury and Gray (Structure (2009)
17: 1636 -- 1648) published a computational algorithm to discern the
specificity determining residues of HIV-1 protease. In this paper we present
two computational tools aimed at re-designing HIV-1 protease, derived from the
algorithm of Chaudhuri and Gray. First, we present an energy-only based
methodology to discriminate cleavable and non cleavable peptides for HIV-1
proteases, both wild type and mutant. Secondly, we show an algorithm we
developed to predict mutant HIV-1 proteases capable of cleaving a new target
substrate peptide, different from the natural targets of HIV-1 protease. The
obtained in silico mutant enzymes were analyzed in terms of cleavability and
specificity towards the target peptide using the energy-only methodology. We
found two mutant proteases as best candidates for specificity and cleavability
towards the target sequence
Core Precession and Global Modes in Granular Bulk Flow
A transition from local to global shear zones is reported for granular flows
in a modified Couette cell. The experimental geometry is a slowly rotating drum
which has a stationary disc of radius R_s fixed at its bottom. Granular
material, which fills this cell up to height H, forms a wide shear zone which
emanates from the discontinuity at the stationary discs edge. For shallow
layers (H/R_s < 0.55), the shear zone reaches the free surface, with the core
of the material resting on the disc and remaining stationary. In contrast, for
deep layers (H/R_s > 0.55), the shear zones meet below the surface and the core
starts to precess. A change in the symmetry of the surface velocities reveals
that this behavior is associated with a transition from a local to a global
shear mode.Comment: 4 pages, 7 figures, submitte
On the Stability of Compactified D=11 Supermembranes
We prove D=11 supermembrane theories wrapping around in an irreducible way
over on the target manifold, have a
hamiltonian with strict minima and without infinite dimensional valleys at the
minima for the bosonic sector. The minima occur at monopole connections of an
associated U(1) bundle over topologically non trivial Riemann surfaces of
arbitrary genus. Explicit expressions for the minimal connections in terms of
membrane maps are presented. The minimal maps and corresponding connections
satisfy the BPS condition with half SUSY.Comment: 15 pages, latex. Added comments in conclusions and more reference
Effects of repeated consumption on sensory-enhanced satiety
Previous research suggests that sensory characteristics of a drink modify the acute satiating effects of its nutrients, with enhanced satiety evident when a high energy drink was thicker and tasted creamier. The present study tested whether this modulation of satiety by sensory context was altered by repeated consumption. Participants (n=48) consumed one of four drinks mid-morning on seven non-consecutive days with satiety responses measured pre-exposure (day 1), post-exposure (day 6) and at a one month follow-up. Drinks combined two levels of energy (lower energy, LE, 326 KJ: higher energy, HE, 1163KJ) with two levels of satiety-predictive sensory characteristics (low-sensory, LS, or enhanced sensory, ES). Test lunch intake 90 minutes after drink consumption depended on both the energy content and sensory characteristics of the drink before exposure, but on energy content alone at post-exposure and the follow-up. The largest change was an increase in test meal intake over time in the LE/LS condition. Effects on intake were reflected in appetite ratings, with rated hunger and expected filling affected by sensory characteristics and energy content pre-exposure, but were largely determined by energy content post exposure and at follow up. In contrast, a measure of expected satiety reflected sensory characteristics regardless of energy content on all three test days. Overall these data suggest that some aspects of the sensory-modulation of satiety are changed by repeated consumption, with covert energy becoming more effective in suppressing appetite over time, but also suggest that these behavioural changes are not readily translated into expectations of satiety
A Computational Methodology to Screen Activities of Enzyme Variants
We present a fast computational method to efficiently screen enzyme activity.
In the presented method, the effect of mutations on the barrier height of an
enzyme-catalysed reaction can be computed within 24 hours on roughly 10
processors. The methodology is based on the PM6 and MOZYME methods as
implemented in MOPAC2009, and is tested on the first step of the amide
hydrolysis reaction catalyzed by Candida Antarctica lipase B (CalB) enzyme. The
barrier heights are estimated using adiabatic mapping and are shown to give
barrier heights to within 3kcal/mol of B3LYP/6-31G(d)//RHF/3-21G results for a
small model system. Relatively strict convergence criteria
(0.5kcal/(mol{\AA})), long NDDO cutoff distances within the MOZYME method
(15{\AA}) and single point evaluations using conventional PM6 are needed for
reliable results. The generation of mutant structure and subsequent setup of
the semiempirical calculations are automated so that the effect on barrier
heights can be estimated for hundreds of mutants in a matter of weeks using
high performance computing
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