Lipids trigger a conformational switch that regulates signal recognition particle (SRP)-mediated protein targeting

Co-translational protein targeting to the membrane is mediated by the signal recognition particle and its receptor (FtsY). Their homologous GTPase domains interact at the membrane and form a heterodimer in which both GTPases are activated. The prerequisite for protein targeting is the interaction of FtsY with phospholipids. However, the mechanism of FtsY regulation by phospholipids remained unclear. Here we show that the N terminus of FtsY (A domain) is natively unfolded in solution and define the complete membrane-targeting sequence. We show that the membrane-targeting sequence is highly dynamic in solution, independent of nucleotides and directly responds to the density of anionic phospholipids by a random coil-helix transition. This conformational switch is essential for tethering FtsY to membranes and activates the GTPase for its subsequent interaction with the signal recognition particle. Our results underline the dynamics of lipid-protein interactions and their importance in the regulation of protein targeting and translocation across biological membranes.     

Crystal structure of the ligand binding domain of netrin G2

Netrin G proteins represent a small family of synaptic cell adhesion molecules related to netrins and to the polymerization domains of laminins. Two netrin G proteins are encoded in vertebrate genomes, netrins G1 and G2, which are known to bind the leucine-rich repeat proteins netrin G ligand (NGL)-1 and NGL-2, respectively. Netrin G proteins share a common multi-domain architecture comprising a laminin N-terminal (LN) domain followed by three laminin epidermal growth factor-like (LE) domains and a C′ region containing a glycosylphosphatidylinositol anchor. Here, we use deletion analysis to show that the LN domain region of netrin Gs contains the binding site for NGLs to which they bind with 1:1 stoichiometry and sub-micromolar affinity. Netrin Gs are alternatively spliced in their LE domain regions, but the binding region, the LN domain, is identical in all splice forms. We determined the crystal structure for a fragment comprising the LN domain and domain LE1 of netrin G2 by sulfur single-wavelength anomalous diffraction phasing and refined it to 1.8 Å resolution. The structure reveals an overall architecture similar to that of laminin α chain LN domains but includes significant differences including a Ca²⁺ binding site in the LN domain. These results reveal the minimal binding unit for interaction of netrin Gs with NGLs, define structural features specific to netrin Gs, and suggest that netrin G alternative splicing is not involved in NGL recognition.     

Novel 9a,11-bridged azalides: One-pot synthesis of N'-substituted 2-imino-1,3-oxazolidines condensed to an azalide aglycone

An efficient one-pot method for the synthesis of novel 9a,11-bridged 15-membered 9a-aza-9-deoxo-9a-homoerythromycin A and its 6-O-methyl analogue has been developed. The novel bicyclic azalide scaffold is characterized by an N′-substituted-2-imino-1,3-oxazolidine moiety bound to a macrolactone ring between positions 9a and 11. Removal of the cladinose sugar from the starting compounds allows easy preparation of a small series of such bicyclic 3-keto and 3,6-hemiketal azalide derivatives. A mechanism for the formation of N′-substituted-2-imino-1,3-oxazolidines is discussed. Antibacterial properties of the prepared compounds were evaluated.     

The effect of handedness on electromyographic activity of human shoulder muscles during movement.

The aim of the study was to investigate whether there was a difference in the electromyographic (EMG) activity of human shoulder muscles between the dominant and nondominant side during movement and to explore whether a possible side-difference depends on the specific task. We compared the EMG activity with surface and intramuscular electrodes in eight muscles of both shoulders in 20 healthy subjects whose hand preference was evaluated using a standard questionnaire. EMG signals were recorded during abduction and external rotation. During abduction, the normalized EMG activity was significantly smaller on the dominant side compared to the nondominant side for all the muscles except for infraspinatus and lower trapezius (P 相似文献   

Escherichia coli signal recognition particle receptor FtsY contains an essential and autonomous membrane-binding amphipathic helix

Escherichia coli membrane protein biogenesis is mediated by a signal recognition particle and its membrane-associated receptor (FtsY). Although crucial for its function, it is still not clear how FtsY interacts with the membrane. Analysis of the structure/function differences between severely truncated active (NG+1) and inactive (NG) mutants of FtsY enabled us to identify an essential membrane-interacting determinant. Comparison of the three-dimensional structures of the mutants, combined with site-directed mutagenesis, modeling, and liposome-binding assays, revealed that FtsY contains a conserved autonomous lipid-binding amphipathic alpha-helix at the N-terminal end of the N domain. Deletion experiments showed that this helix is essential for FtsY function in vivo, thus offering, for the first time, clear evidence for the functionally important, physiologically relevant interaction of FtsY with lipids.     

What distinguishes the Olympic level heavyweight rowers from other internationally successful rowers?

The aim of the study was to determine which of the observed variables differentiate mostly the successful (Olympic Games contenders) from the less successful rowers (Internationally competitive rowers) and in order for that anthropometric and physiological profile of elite Croatian heavyweight rowers was assessed. Twenty nine national rowing champions were divided into two groups according to their international competitive achievements. Physiological characteristics were assessed during a continuous progressive rowing ergometer test. Differences were determined using the independent t-test with Bonferroni corrections. Successful rowers had somewhat larger values of almost all of the observed lengths, widths and girths (exceptions: chest and thigh girth). In addition, their maximal oxygen uptake was significantly higher (5.51 +/- 0.40 L/min vs. 5.16 +/- 0.39 L/min; p < 0.05) as was their power output at anaerobic threshold (346.3 +/-17.9 W vs. 319.2 +/- 20.1 W; p < 0.01). Less successful Croatian rowers should target their training in the upcoming years towards increasing, primarily, maximal oxygen uptake and power output at anaerobic threshold.     

Two new phenylpiperazines with atypical antipsychotic potential

Two new series of substituted arylpiperazines with heterocyclic 3-propoxy-benzimidazole or 3-propoxy-benzimidazole-2-thione groups were synthesized and their in vitro binding affinities for the D(2), 5-HT(1A), 5-HT(2A), and alpha(1)-adrenergic receptors determined. Among them, only two compounds with phenyl aryl-constituent (8a and 9a) showed 5-HT(2A)/D(2) pK(i) binding ratios proposed for atypical neuroleptics. As to their behavioral screening on rodents, both compounds exhibited a non-cataleptic action in rats and antagonized D-amphetamine-induced hyperlocomotion in mice, suggesting their possible atypical antipsychotic potency.     

Novel 9a-carbamoyl- and 9a-thiocarbamoyl-3-decladinosyl-6-hydroxy and 6-methoxy derivatives of 15-membered macrolides

An efficient method for the synthesis of diverse 9a-carbamoyl- and 9a-thiocarbamoyl-3-decladinosyl-6-hydroxy and 3-decladinosyl-6-methoxy derivatives of 15-membered azalides has been developed. These derivatives bear various alkyl and aryl groups attached to macrolide scaffold through urea or thiourea moieties at 9a position. Chemical transformations of hydroxy group at position C-3 afforded range of ketolides, anhydrolides, hemiketals, cyclic ethers, and acylides. It has been shown that 6-hydroxy and 6-methoxy derivatives undergo different chemical transformations under otherwise identical reaction conditions. Antimicrobial properties of prepared compounds were evaluated.