YidC and SecY mediate membrane insertion of a type I transmembrane domain

YidC has been identified recently as an evolutionary conserved factor that is involved in the integration of inner membrane proteins (IMPs) in Escherichia coli. The discovery of YidC has inspired the reevaluation of membrane protein assembly pathways in E. coli. In this study, we have analyzed the role of YidC in membrane integration of a widely used model IMP, leader peptidase (Lep). Site-directed photocross-linking experiments demonstrate that both YidC and SecY contact nascent Lep very early during biogenesis, at only 50-amino acid nascent chain length. At this length the first transmembrane domain (TM), which acquires a type I topology, is not even fully exposed outside the ribosome. The pattern of interactions appears dependent on the position of the cross-linking probe in the nascent chain. Upon elongation, nascent Lep remains close to YidC and comes into contact with lipids as well. Our results suggest a role for YidC in both the reception and lipid partitioning of type I TMs

Atypical periosteal osteoid osteoma: a case report

Osteoid osteoma is a benign osteoblastic tumor usually seen in adolescent and young males. In the paediatric age group, since the history may be difficult to elicit, there are often problems in early diagnosis. The author reports an unusual presentation of osteoid osteoma in a ten-year-old girl, which could not be diagnosed by conventional X-rays and CT scan

Flexibility in targeting and insertion during bacterial membrane protein biogenesis.

The biogenesis of Escherichia coli inner membrane proteins (IMPs) is assisted by targeting and insertion factors such as the signal recognition particle (SRP), the Sec-translocon and YidC with translocation of (large) periplasmic domains energized by SecA and the proton motive force (pmf). The use of these factors and forces is probably primarily determined by specific structural features of an IMP. To analyze these features we have engineered a set of model IMPs based on endogenous E. coli IMPs known to follow distinct targeting and insertion pathways. The modified model IMPs were analyzed for altered routing using an in vivo protease mapping approach. The data suggest a facultative use of different combinations of factors. © 2007 Elsevier Inc. All rights reserved

Estimating the size of the active translocation pore of an autotransporter.

Autotransporters (ATs) are large virulence factors secreted by Gram-negative bacteria. The passenger domain, carrying the virulence functions, is transported across the bacterial outer membrane in a step that is facilitated by a C-terminal β-domain. This domain folds into a β-barrel with a central aqueous pore of ∼ 1 nm inner diameter according to crystal structures. However, these static dimensions are not compatible with the observed secretion of passengers that may contain natural short-spaced disulfide bonds or artificially fused folded elements. Here, we have systematically analyzed the dimensions of the active AT passenger translocator by inserting peptides of different length and structural complexity in the passenger of the AT hemoglobin protease. The peptides were introduced in a short loop protruding from the main structure and flanked by two single cysteines. Our results show that the attained secondary structure may be more critical for secretion than the length of peptide inserted. Furthermore, the data suggest that, during passenger translocation, at least four extended polypeptides or an extended polypeptide and an α-helix are accommodated in the translocator, indicating that the diameter of the active translocation pore is up to 1.7 nm. If the β-domain functions as the translocator, it must be forced into an expanded conformation during passenger translocation. © 2011 Elsevier Ltd. All rights reserved

The two membrane segments of leader peptidase partition one by one into the lipid bilayer via a Sec/YidC interface.

We have addressed the mechanism of insertion of both transmembrane segments (TMs) of leader peptidase, a double-spanning protein, into the Escherichia coli inner membrane. Using photo-crosslinking, the first TM (H1) was shown to insert at a Sec-translocon/YidC interface in a fixed orientation. H1 lost its contacts with the Sec-translocon and gained access to lipids near YidC soon after complete exposure outside the ribosome. Following lipid integration, it moved away from the Sec/YidC insertion site. The second TM (H2) inserted and interacted with SecY and YidC in a similar transient fashion. The data are consistent with a linear integration model in which the TMs of polytopic inner membrane proteins move one by one from a Sec/YidC insertion site into the lipid bilayer. We propose that YidC assists the lipid partitioning of single TMs. © 2004 European Molecular Biology Organization

Molecular characterization of Escherichia coli FtsE and FtsX.

The genes ftsE and ftsX are organized in one operon together with ftsY. FtsY codes for the receptor of the signal recognition particle (SRP) that functions in targeting a subset of inner membrane proteins. We have found no indications for a structural relationship between FtsE/X and FtsY. Evidence is presented that FtsE and FtsX form a complex in the inner membrane that bears the characteristics of an ATP-binding cassette (ABC)-type transporter. FtsE is a hydrophilic nucleotide-binding protein that has a tendency to dimerize and associates with the inner membrane through an interaction with the integral membrane protein FtsX. An FtsE null mutant showed filamentous growth and appeared viable on high salt medium only, indicating a role for FtsE in cell division and/or salt transport

Evaluation of pharmacological aids on physical performance after a transmeridian flight

Effets de la caféine et de la mélatonine sur les problèmes liés au décalage horaire (baisse des performances, fatigue...) chez des réservistes de l'U.S. Air Force ayant effectués un vol sur sept fuseaux horaires en direction de l'est