Structural Biology of Bacterial Multidrug Resistance Gene Regulators

Multidrug resistance (mdr)1 can be defined broadly as the ability of a cell to survive ordinarily lethal doses of more than one drug. Clearly, such resistance is a critical problem in the treatment of fungal and bacterial infections and cancer. Four general, but nonexclusive, mechanisms give rise to multidrug resistance: 1) detoxification by enzymatic modification or cleavage of drug; 2) genetic alteration of the intra- or extracellular targets; 3) decreased permeability of the cell membrane; and 4) active drug extrusion by multidrug transporters. Paramount to our understanding of mdr is the issue of recognition of structurally dissimilar substrates and how drug binding effects function. In bacteria many multidrug transporters are regulated directly (locally) by transcription factors, which also bind the substrates of these transporters, i.e. the drug can act as a transcriptional coactivator or inducer. Multiple mdr transporter genes are also regulated globally by activators such as MarA that do not necessarily bind drugs (1). The regulators are of keen interest because they are more amenable to structural studies than the membrane-bound transporters and thus offer a greater chance to obtain high resolution views of multidrug binding. Moreover, the local gene regulators are equally interesting as their DNA complexes directly reveal the mechanism of mdrtransporter gene regulation. This minireview will summarize the structures of known bacterial mdr regulators. Because our focus is more structural the reader is referred to one of several recent reviews that discuss the more biological aspects of global and local mdr regulation (2-5)

The pUL37 tegument protein guides alphaherpesvirus retrograde axonal transport to promote neuroinvasion

A hallmark property of the neurotropic alpha-herpesvirinae is the dissemination of infection to sensory and autonomic ganglia of the peripheral nervous system following an initial exposure at mucosal surfaces. The peripheral ganglia serve as the latent virus reservoir and the source of recurrent infections such as cold sores (herpes simplex virus type I) and shingles (varicella zoster virus). However, the means by which these viruses routinely invade the nervous system is not fully understood. We report that an internal virion component, the pUL37 tegument protein, has a surface region that is an essential neuroinvasion effector. Mutation of this region rendered herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV) incapable of spreading by retrograde axonal transport to peripheral ganglia both in culture and animals. By monitoring the axonal transport of individual viral particles by time-lapse fluorescence microscopy, the mutant viruses were determined to lack the characteristic sustained intracellular capsid motion along microtubules that normally traffics capsids to the neural soma. Consistent with the axonal transport deficit, the mutant viruses did not reach sites of latency in peripheral ganglia, and were avirulent. Despite this, viral propagation in peripheral tissues and in cultured epithelial cell lines remained robust. Selective elimination of retrograde delivery to the nervous system has long been sought after as a means to develop vaccines against these ubiquitous, and sometimes devastating viruses. In support of this potential, we find that HSV-1 and PRV mutated in the effector region of pUL37 evoked effective vaccination against subsequent nervous system challenges and encephalitic disease. These findings demonstrate that retrograde axonal transport of the herpesviruses occurs by a virus-directed mechanism that operates by coordinating opposing microtubule motors to favor sustained retrograde delivery of the virus to the peripheral ganglia. The ability to selectively eliminate the retrograde axonal transport mechanism from these viruses will be useful in trans-synaptic mapping studies of the mammalian nervous system, and affords a new vaccination paradigm for human and veterinary neurotropic herpesviruses

The structure of Herpesvirus Fusion Glycoprotein B-Bilayer Complex reveals the protein-membrane and lateral protein-protein interaction

Glycoprotein B (gB) is a key component of the complex herpesvirus fusion machinery. We studied membrane interaction of two gB ectodomain forms and present an electron cryotomography structure of the gB-bilayer complex. The two forms differed in presence or absence of the membrane proximal region (MPR) but showed an overall similar trimeric shape. The presence of the MPR impeded interaction with liposomes. In contrast, the MPR-lacking form interacted efficiently with liposomes. Lateral interaction resulted in coat formation on the membranes. The structure revealed that interaction of gB with membranes was mediated by the fusion loops and limited to the outer membrane leaflet. The observed intrinsic propensity of gB to cluster on membranes indicates an additional role of gB in driving the fusion process forward beyond the transient fusion pore opening and subsequently leading to fusion pore expansion

DNA binding shifts the redox potential of the transcription factor SoxR

Electrochemistry measurements on DNA-modified electrodes are used to probe the effects of binding to DNA on the redox potential of SoxR, a transcription factor that contains a [2Fe-2S] cluster and is activated through oxidation. A DNA-bound potential of +200 mV versus NHE (normal hydrogen electrode) is found for SoxR isolated from Escherichia coli and Pseudomonas aeruginosa. This potential value corresponds to a dramatic shift of +490 mV versus values found in the absence of DNA. Using Redmond red as a covalently bound redox reporter affixed above the SoxR binding site, we also see, associated with SoxR binding, an attenuation in the Redmond red signal compared with that for Redmond red attached below the SoxR binding site. This observation is consistent with a SoxR-binding-induced structural distortion in the DNA base stack that inhibits DNA-mediated charge transport to the Redmond red probe. The dramatic shift in potential for DNA-bound SoxR compared with the free form is thus reconciled based on a high-energy conformational change in the SoxR–DNA complex. The substantial positive shift in potential for DNA-bound SoxR furthermore indicates that, in the reducing intracellular environment, DNA-bound SoxR is primarily in the reduced form; the activation of DNA-bound SoxR would then be limited to strong oxidants, making SoxR an effective sensor for oxidative stress. These results more generally underscore the importance of using DNA electrochemistry to determine DNA-bound potentials for redox-sensitive transcription factors because such binding can dramatically affect this key protein property

Temperatura de flores e síliquas de canola (Brassica napus L.) durante ocorrência de geada.

Orientador: Genei Antonio Dalmago

Eficiência de uso da radiação fotossinteticamente ativa em canola sob distintos espaçamentos.

A radiação solar é a fonte primária de energia para vários processos vitais do ecossistema, dentre eles destaca-se o crescimento vegetal e seu acúmulo de fotoassimilados. Neste contexto, a mensuração da radiação fotossinteticamente ativa interceptada (RFAin) por dosséis de plantas e sua interação com as diferentes estruturas da planta, especialmente as folhas, condiciona a capacidade de crescimento e produção

Water excess in different phenological stages of canola cultivars.

The objective of this study was to determine the stage of development with greater sensitivity to water excess and the period of time required to compromise the emergence and grain yield components of canola. The experiments were performed in a greenhouse at the Federal University of Santa Maria and at the Farroupilha Federal Institute, Campus of São Vicente do Sul, RS during the 2015 agricultural year. The completely randomized experimental design was utilized to investigate phenological stages and periods of continuous water excess in the soil. Also, factors like percentage of emergence, emergence speed index, grain yield, number of siliques per plant, one hundred grains weight, dry matter of aerial part, silique length, number of grains per silique, and weight of 20 siliques were determined. The stages of rosette leaf formation and beginning of anthesis are the most sensitive to water excess in the soil. Water excess for 24 h is enough to reduce the emergence speed index. However, the percentage of emergence is not compromised by water excess up to 192 continuous hours. 24 h of water excess reduces the number of siliques per plant, dry matter of aerial part and grain yield of canola