Membrane Protein Biogenesis in Ffh- or FtsY-Depleted Escherichia coli

BACKGROUND: The Escherichia coli version of the mammalian signal recognition particle (SRP) system is required for biogenesis of membrane proteins and contains two essential proteins: the SRP subunit Ffh and the SRP-receptor FtsY. Scattered in vivo studies have raised the possibility that expression of membrane proteins is inhibited in cells depleted of FtsY, whereas Ffh-depletion only affects their assembly. These differential results are surprising in light of the proposed model that FtsY and Ffh play a role in the same pathway of ribosome targeting to the membrane. Therefore, we decided to evaluate these unexpected results systematically. METHODOLOGY/PRINCIPAL FINDINGS: We characterized the following aspects of membrane protein biogenesis under conditions of either FtsY- or Ffh-depletion: (i) Protein expression, stability and localization; (ii) mRNA levels; (iii) folding and activity. With FtsY, we show that it is specifically required for expression of membrane proteins. Since no changes in mRNA levels or membrane protein stability were detected in cells depleted of FtsY, we propose that its depletion may lead to specific inhibition of translation of membrane proteins. Surprisingly, although FtsY and Ffh function in the same pathway, depletion of Ffh did not affect membrane protein expression or localization. CONCLUSIONS: Our results suggest that indeed, while FtsY-depletion affects earlier steps in the pathway (possibly translation), Ffh-depletion disrupts membrane protein biogenesis later during the targeting pathway by preventing their functional assembly in the membrane

Battling out of the home front: Women in uniform during World War One

En el otoño de 1914 las mujeres de los países occidentales tomaron la iniciativa de afrontar la guerra y tomar parte activa en ella. Lo hicieron a la manera diversa en que los seres humanos afrontan los problemas: en la difícil cotidianidad del que aguarda el regreso de los soldados, soportando todo el esfuerzo del sostenimiento familiar, o colaborando en los trabajos producción para la vida civil y militar. Pero no pocas empujaron a los gobiernos para que les permitieran luchar dentro de los ejércitos, llevando los uniformes militares y mostrando los colores de la patria. Estas líneas son su historia.In the fall of 1914 western women began their way to cope with war taking an active part in it. They did it in the various ways human beings usually face problems: awaiting the return of the soldiers in the everyday difficulties, supporting all the works of family´s needs, or helping in the country production work for the civil and military life. But also, not few women pushed governments to allow them fighting in armies, wearing military uniforms and showing the colors of their country. This text shows their history

Dynamics of allosteric transitions in GroEL

The chaperonin GroEL-GroES, a machine which helps some proteins to fold, cycles through a number of allosteric states, the $T$ state, with high affinity for substrate proteins (SPs), the ATP-bound $R$ state, and the $R^{\prime\prime}$ ($GroEL-ADP-GroES$) complex. Structures are known for each of these states. Here, we use a self-organized polymer (SOP) model for the GroEL allosteric states and a general structure-based technique to simulate the dynamics of allosteric transitions in two subunits of GroEL and the heptamer. The $T \to R$ transition, in which the apical domains undergo counter-clockwise motion, is mediated by a multiple salt-bridge switch mechanism, in which a series of salt-bridges break and form. The initial event in the $R \to R^{\prime\prime}$ transition, during which GroEL rotates clockwise, involves a spectacular outside-in movement of helices K and L that results in K80-D359 salt-bridge formation. In both the transitions there is considerable heterogeneity in the transition pathways. The transition state ensembles (TSEs) connecting the $T$, $R$, and $R^{\prime\prime}$ states are broad with the the TSE for the $T \to R$ transition being more plastic than the $R\to R^{\prime\prime}$ TSE. The results suggest that GroEL functions as a force-transmitting device in which forces of about (5-30) pN may act on the SP during the reaction cycle.Comment: 32 pages, 10 figures (Longer version than the one published

DEVELOPMENT OF TEACHING MATERIALS IN WRITING DESCRIPTIVE TEXTS OF VOCATIONAL SCHOOL STUDENTS

The objective of the study is to develop the teaching materials in writing descriptive texts in Grade X students of SMK Binaan UMN Al-Washliyah 3, Medan. The study is conducted by  the Development Research method, and the evaluators are the instructors of the Indonesian Subject (specific instructors), and the subjects are Grade X students. Pre-test and post-test are done to find out the effectiveness of the result. The result of the pre-test shows that the average score is 67% with the category of satisfactory; the result of the post-test shows that the average score is 85% with the category of distinction. The process of developing teaching materials includes three aspects of assessment: 1) teaching materials, 2) presentation, and 3) language structure. The validation of material experts includes content with an average score of 4.9% and a percentage of 82.2% with the category of distinction. The feasibility of presenting teaching materials has an average score of 113% with the category of distinction, and the language element has an average score of 11.4% with the category of distinction. The conclusion indicates that the design for developing teaching materials of descriptive texts by using a scientific approach in the subject of Indonesian is very effective

RPA2 (replication protein A2, 32kDa)

Review on RPA2 (replication protein A2, 32kDa), with data on DNA, on the protein encoded, and where the gene is implicated

Conformational changes in the GTPase modules of the signal reception particle and its receptor drive initiation of protein translocation

During cotranslational protein targeting, two guanosine triphosphatase (GTPase) in the signal recognition particle (SRP) and its receptor (SR) form a unique complex in which hydrolyses of both guanosine triphosphates (GTP) are activated in a shared active site. It was thought that GTP hydrolysis drives the recycling of SRP and SR, but is not crucial for protein targeting. Here, we examined the translocation efficiency of mutant GTPases that block the interaction between SRP and SR at specific stages. Surprisingly, mutants that allow SRP–SR complex assembly but block GTPase activation severely compromise protein translocation. These mutations map to the highly conserved insertion box domain loops that rearrange upon complex formation to form multiple catalytic interactions with the two GTPs. Thus, although GTP hydrolysis is not required, the molecular rearrangements that lead to GTPase activation are essential for protein targeting. Most importantly, our results show that an elaborate rearrangement within the SRP–SR GTPase complex is required to drive the unloading and initiate translocation of cargo proteins

The Impact of Base Stacking on the Conformations and Electrostatics of Single-Stranded DNA

Single-stranded DNA (ssDNA) is notable for its interactions with ssDNA binding proteins (SSBs) during fundamentally important biological processes including DNA repair and replication. Previous work has begun to characterize the conformational and electrostatic properties of ssDNA in association with SSBs. However, the conformational distributions of free ssDNA have been difficult to determine. To capture the vast array of ssDNA conformations in solution, we pair small angle X-ray scattering with novel ensemble fitting methods, obtaining key parameters such as the size, shape and stacking character of strands with different sequences. Complementary ion counting measurements using inductively coupled plasma atomic emission spectroscopy are employed to determine the composition of the ion atmosphere at physiological ionic strength. Applying this combined approach to poly dA and poly dT, we find that the global properties of these sequences are very similar, despite having vastly different propensities for single-stranded helical stacking. These results suggest that a relatively simple mechanism for the binding of ssDNA to non-specific SSBs may be at play, which explains the disparity in binding affinities observed for these systems