Radiation Damage and Racemic Protein Crystallography Reveal the Unique Structure of the GASA/Snakin Protein Superfamily

Proteins from the GASA/snakin superfamily are common in plant proteomes and have diverse functions, including hormonal crosstalk, development, and defense. One 63‐residue member of this family, snakin‐1, an antimicrobial protein from potatoes, has previously been chemically synthesized in a fully active form. Herein the 1.5 Å structure of snakin‐1, determined by a novel combination of racemic protein crystallization and radiation‐damage‐induced phasing (RIP), is reported. Racemic crystals of snakin‐1 and quasi‐racemic crystals incorporating an unnatural 4‐iodophenylalanine residue were prepared from chemically synthesized d ‐ and l ‐proteins. Breakage of the C?I bonds in the quasi‐racemic crystals facilitated structure determination by RIP. The crystal structure reveals a unique protein fold with six disulfide crosslinks, presenting a distinct electrostatic surface that may target the protein to microbial cell surfaces.     

Escherichia coli quinolinate synthetase does indeed harbor a [4Fe-4S] cluster

Quinolinic acid is an intermediate in the biosynthesis of nicotinamide-containing redox cofactors. The ultimate step in the formation of quinolinic acid in prokaryotes is the condensation of iminosuccinate and dihydroxyacetone phosphate, which is catalyzed by the product of the nadA gene in Escherichia coli. A combination of UV-vis, M?ssbauer, and EPR spectroscopies, along with analytical methods for the determination of iron and sulfide, demonstrates for the first time that anaerobically purified quinolinate synthetase (NadA) from E. coli contains one [4Fe-4S] cluster per polypeptide. The protein is active, catalyzing the formation of quinolinic acid with a Vmax [ET]-1 of 0.01 s-1.     

Comparison of various types of coherence and emergent coherent systems

Coherence is a collective property that is present in Bose–Einstein condensates (BEC), an example of which when charged is superconductivity (SC). Coherence is also believed to be present to a degree in highly efficient energy transfer in certain biological systems. Attributes of coherent systems are examined in BEC, superfluidity and Bardeen, Cooper, and Schrieffer SC and a laser in part 1. Part 2 consists of examination of various proposals for coherence including “emergent coherent systems” where there may be coherence but no phase transition. We discuss “cold” atomic gases, the Casimir effect, an extended version of Förster's resonance energy transfer, Fröhlich's model, exciton‐coupled quantum wells, and conceptually “old” polaritons rejuvenated by new developments. A discussion about highly efficient energy transfer in photosynthesis along with our proposal for a possible new model for this system is the last of the examples. We finish with a discussion about emergent coherent systems and attempt to classify the examples of parts 1 and 2. © 2013 Wiley Periodicals, Inc.     

A quasi-similarity analysis of the turbulent boundary layer on a flat plate

The partial differential equation of the boundary layer on a flat plate are simplified by using the universal variables for turbulent flow. For laminar flow this gives boundary layer having a finite thickness and a friction coefficient differing by a few percent from the Blasius value. For a turbulent flow a differential equation for the velocity distribution is obtained with a parameter which varies slowly with the streamwise coordinate. The numerical value of this parameter is determined as an eigenvalue of the differential equations giving a velocity profile which evolves as the boundary layer thickens. Numerical calculations using a simple eddy viscosity model gave results in very good agreement with experiment.     

A comparison of the lift of flat delta wings and waveriders at high angles of incidence and high mach number

Summary It has been suggested that in the conditions of lifting re-entry caret wings are likely to have higher lift coefficients than flat-bottomed wings with the same ratio of lift to drag. Thus, for given speed and wing loading, they can re-enter at higher altitudes with a consequent reduction in stagnation point heating rate. In this paper thin-shock-layer theory is used to study the lifting properties of caret and flat-bottomed wings and of wings with concave lower surfaces. It is found that significant gains in lift coefficient can be achieved with moderately recessed lower surfaces. These results hold for both perfect and real gas flows.

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Übersicht Man hat vermutet, daß dachartig geknickte Auftriebsflächen beim Wiedereintritt in die Erdatmosphäre einen größeren Auftriebskoeffizienten haben als flache Flügel mit demselben Verhältnis von Auftrieb zu Widerstand. Auf diese Weise können sie bei gegebener Geschwindigkeit und Flügelbelastung bei größeren Höhen wieder eintreten und führen dabei zu einer geringeren Erhitzung im Staupunkt. In der vorliegenden Arbeit wird eine auf der Annahme einer dünnen Stoßschicht basierende Theorie verwendet, um die Auftriebseigenschaften von gefalteten und flachen Deltaflügeln sowie von Flügeln mit konkaver Unterseite zu untersuchen. Es stellt sich heraus, daß eine bedeutende Verbesserung des Auftriebskoeffizienten durch schwach eingeknickte Unterseiten erreicht werden kann. Diese Ergebnisse gelten sowohl für ideale wie auch für reale Gasströmungen.