Thymic stromal lymphopoietin (TSLP) is an interleukin (IL)-

No abstract

The ATP-dependent integral membrane protease FtsH is universally conserved in bacteria. Orthologs exist in chloroplasts and mitochondria, where in humans the loss of a close FtsH-homolog causes a form of spastic paraplegia. FtsH plays a crucial role in quality control by degrading unneeded or damaged membrane proteins, but it also targets soluble signaling factors like 32 and -CII. We report here the crystal structure of a soluble FtsH construct that is functional in caseinolytic and ATPase assays. The molecular architecture of this hexameric molecule consists of two rings where the protease domains possess an all-helical fold and form a flat hexagon that is covered by a toroid built by the AAA domains. The active site of the protease classifies FtsH as an Asp-zincin, contrary to a previous report. The different symmetries of protease and AAA rings suggest a possible translocation mechanism of the target polypeptide chain into the interior of the molecule where the proteolytic sites are located.AAA ͉ protease ͉ protein degradation ͉ x-ray A TP-dependent proteases play crucial roles in protein quality control and regulation (for reviews, see refs. 1 and 2). One of these is FtsH, initially described as a temperature-sensitive and cell-division-defective mutant, which is also called HflB, named after a high-frequency of lysogenization locus of bacteriophage . FtsH is an integral membrane protease found in bacteria, chloroplasts, and mitochondria (reviewed in ref.3) (Fig. 6, which is published as supporting information on the PNAS web site). In bacteria, FtsH malfunction causes severe phenotypes like cell division defects and growth arrest (4, 5) (reviewed in ref.3). Deletion of the human mitochondrial homolog paraplegin, which shares 40% sequence identity with FtsH from Escherichia coli, is responsible for an autosomal recessive form of hereditary spastic paraplegia (6). The N terminus of FtsH contains two transmembrane helices followed by an AAA module (ATPases associated with various cellular activities), including the SRH (second region of homology) (3). The C-terminal part of the polypeptide chain bears the HEXXH motif that is characteristic for Zn-dependent metalloproteases, where the two histidines coordinate to the zinc ion and the glutamate serves as a catalytic base. In bacteria, the AAA and protease domains are located on the cytosolic side of the membrane. Of the five ATP-dependent proteases in E. coli, HslVU, Lon, ClpXP, ClpAP, and FtsH, the last is the only one that is essential and universally conserved in bacteria. It degrades membrane proteins like the uncomplexed SecY subunit of translocase (7), the a-subunit of F o F 1 -ATPase (8), and the photosystem in chloroplasts (9), therefore playing an important role in the quality control of membrane proteins. Further targets comprise regulatory soluble proteins such as 32 (10, 11) or -CII transcriptional activator protein (12). All these substrates are degraded in an ATP-dependent manner where the energy is used for pulling the proteins out of the membran...

Th17 cells have been recognized as the central effectors in organ-related autoimmune diseases. IL-6 is a key factor that reciprocally regulates Th17 and Foxp3 + Treg differentiation by inhibition of TGF-b induced Foxp3 and induction of RORct, a Th17 lineage-specific transcription factor. Recently IL-21 has been suggested to induce RORct and Th17 development in the absence of IL-6. However, the relevance of IL-21 for Th17-dependent inflammatory responses in vivo remains unclear. In this study, we demonstrate that differentiation of IL-17-producing CD4 T cells, their recruitment to inflamed organs, and the development of autoimmune disease was not affected in il21R -/-and il21 -/-mice in models of myelin oligodendrocyte glycoprotein-induced autoimmune encephalitis and autoimmune myocarditis. IL-6 induced Th17 differentiation independent of and much more potently than IL-21 in vitro. These data suggest that IL-6 is sufficient to drive Th17 development and associated autoimmunity in vivo in the absence of IL-21 or IL-21R.

Lipase LipA from Serratia marcescens is a 613-amino acid enzyme belonging to family I.3 of lipolytic enzymes that has an important biotechnological application in the production of a chiral precursor for the coronary vasodilator diltiazem. Like other family I.3 lipases, LipA is secreted by Gram-negative bacteria via a type I secretion system and possesses 13 copies of a calcium binding tandem repeat motif, GGXGXDXUX (U, hydrophobic amino acids), in the C-terminal part of the polypeptide chain. The 1.8-Å crystal structure of LipA reveals a close relation to eukaryotic lipases, whereas family I.1 and I.2 enzymes appear to be more distantly related. Interestingly, the structure shows for the N-terminal lipase domain a variation on the canonical ␣/␤ hydrolase fold in an open conformation, where the putative lid helix is anchored by a Ca 2؉ ion essential for activity. Another novel feature observed in this lipase structure is the presence of a helical hairpin additional to the putative lid helix that exposes a hydrophobic surface to the aqueous medium and might function as an additional lid. The tandem repeats form two separated parallel ␤-roll domains that pack tightly against each other. Variations of the consensus sequence of the tandem repeats within the second ␤-roll result in an asymmetric Ca 2؉ binding on only one side of the roll. The analysis of the properties of the ␤-roll domains suggests an intramolecular chaperone function.