Shaping the Borrelia burgdorferi genome: crystal structure and binding properties of the DNA-bending protein Hbb

The genome of the Lyme disease-causing spirochete Borrelia burgdorferi encodes only a single polypeptide from the integration host factor (IHF)/HU or 'DNABII' family of nucleoid-associated proteins - Hbb. DNABII proteins induce large bends in DNA and serve as architectural factors in a variety of prokaryotic cellular processes. We have solved the crystal structure of an Hbb-DNA complex in which the DNA is bent by over 180 degrees . We find that like IHF, Hbb relies exclusively on indirect readout to recognize its cognate site. Additional binding studies show that the sequence preferences of Hbb are related to, yet distinct from those of IHF. Defining these binding characteristics may help to uncover additional roles for Hbb in Borrelia DNA metabolism as well as further our understanding of the mechanism of indirect readout.     

Loss of miR-203 regulates cell shape and matrix adhesion through ROBO1/Rac/FAK in response to stiffness

Breast tumor progression is accompanied by changes in the surrounding extracellular matrix (ECM) that increase stiffness of the microenvironment. Mammary epithelial cells engage regulatory pathways that permit dynamic responses to mechanical cues from the ECM. Here, we identify a SLIT2/ROBO1 signaling circuit as a key regulatory mechanism by which cells sense and respond to ECM stiffness to preserve tensional homeostasis. We observed that Robo1 ablation in the developing mammary gland compromised actin stress fiber assembly and inhibited cell contractility to perturb tissue morphogenesis, whereas SLIT2 treatment stimulated Rac and increased focal adhesion kinase activity to enhance cell tension by maintaining cell shape and matrix adhesion. Further investigation revealed that a stiff ECM increased Robo1 levels by down-regulating miR-203. Consistently, patients whose tumor expressed a low miR-203/high Robo1 expression pattern exhibited a better overall survival prognosis. These studies show that cells subjected to stiffened environments up-regulate Robo1 as a protective mechanism that maintains cell shape and facilitates ECM adherence.     

Molecular evolution of streptococcal M protein: cloning and nucleotide sequence of the type 24 M protein gene and relation to other genes of Streptococcus pyogenes.

The structural gene for the type 24 M protein of group A streptococci has been cloned and expressed in Escherichia coli. The complete nucleotide sequence of the gene and the 3' and 5' flanking regions was determined. The sequence includes an open reading frame of 1,617 base pairs encoding a pre-M24 protein of 539 amino acids and a predicted Mr of 58,738. The structural gene contains two distinct tandemly reiterated elements. The first repeated element consists of 5.3 units, and the second contains 2.7 units. Each element shows little variation of the basic 35-amino-acid unit. Comparison of the sequence of the M24 protein with the sequence of the M6 protein (S. K. Hollingshead, V. A. Fischetti, and J. R. Scott, J. Biol. Chem. 261:1677-1686, 1986) indicates that these molecules have are conserved except in the regions coding for the antigenic (type specific) determinant and they have three regions of homology within the structural genes: 38 of 42 amino acids within the amino terminal signal sequence, the second repeated element of the M24 protein is found in the M6 molecule at the same position in the protein, and the carboxy terminal 164 amino acids, including a membrane anchor sequence, are conserved in both proteins. In addition, the sequences flanking the two genes are strongly conserved.     

In vivo and in vitro characterization of novel microparticulates based on hyaluronan and chitosan hydroglutamate

This study examined the application of previously characterized microparticles composed of hyaluronan (HA) and chitosan hydroglutamate (CH) as well as novel microparticles consisting of both polymers (HA/CH) to improve the nasal delivery of a model drug. The rabbit bioavailabilities of gentamicin incorporated in HA, CH, and HA/CH microparticles were increased 23-, 31-, and 42-fold, respectively, compared with the control intranasal solution of gentamicin, indicating that all test microparticles were retained for longer periods on the nasal mucosa of the rabbits as supported by previous in vitro dissolution as well as frog palate mucoadhesion studies, thereby improving drug absorption. The higher bioavailabilities of CH-based formulations (CH and HA/CH) suggest the penetration-enhancing effects of CH may also be partially responsible for the improvement. A model was developed, based on a glass impinger device, to deliver dry powder formulations reproducibly onto the surface of cultured cell monolayers. In vitro permeability and fluorescence microscopy studies on the tight junctions of the 16HBE14o- cell lines further confirmed the ability of CH-based formulations to enhance penetration. Furthermore, the in vitro absorption profile from cell culture studies was consistent with those determined from in vivo studies. The complementary effect from the mucoadhesive nature of HA coupled with the penetration-enhancing effects of CH makes the novel HA/CH formulation a promising nasal delivery system.     

One new genus and three new species of Orsillinae (Hemiptera: Lygaeidae) from Australia

Abstract  Two new species of Nysius Dallas, N. orarius sp. n. and N. tasmaniensis sp. n. are described from New South Wales and Tasmania (Australia), respectively. A new monotypic genus, Reticulatonysius , with type-species R. queenslandensis sp. n. is described from Queensland, and its systematic relationship with other orsilline genera is discussed.     

What Took Them So Long? Explaining PhD Delays among Doctoral Candidates

A delay in PhD completion, while likely undesirable for PhD candidates, can also be detrimental to universities if and when PhD delay leads to attrition/termination. Termination of the PhD trajectory can lead to individual stress, a loss of valuable time and resources invested in the candidate and can also mean a loss of competitive advantage. Using data from two studies of doctoral candidates in the Netherlands, we take a closer look at PhD duration and delay in doctoral completion. Specifically, we address the question: Is it possible to predict which PhD candidates will experience delays in the completion of their doctorate degree? If so, it might be possible to take steps to shorten or even prevent delay, thereby helping to enhance university competitiveness. Moreover, we discuss practical do''s and don''ts for universities and graduate schools to minimize delays.     

Arginine as a General Acid Catalyst in Serine Recombinase-mediated DNA Cleavage

Members of the serine family of site-specific DNA recombinases use an unusual constellation of amino acids to catalyze the formation and resolution of a covalent protein-DNA intermediate. A recent high resolution structure of the catalytic domain of Sin, a particularly well characterized family member, provided a detailed view of the catalytic site. To determine how the enzyme might protonate and stabilize the 3′O leaving group in the strand cleavage reaction, we examined how replacing this oxygen with a sulfur affected the cleavage rate by WT and mutant enzymes. To facilitate direct comparison of the cleavage rates, key experiments used suicide substrates that prevented religation after cleavage. The catalytic defect associated with mutation of one of six highly conserved arginine residues, Arg-69 in Sin, was partially rescued by a 3′ phosphorothiolate substrate. We conclude that Arg-69 has an important role in stabilizing the 3′O leaving group and is the prime candidate for the general acid that protonates the 3′O, in good agreement with the position it occupies in the high resolution structure of the active site of Sin.