Identification of the mitochondrial MSRB2 as a binding partner of LG72

Genetic studies have linked the evolutionary novel, anthropoid primate-specific gene locus G72/G30 in the etiology of schizophrenia and other psychiatric disorders. However, the function of the protein encoded by this locus, LG72, is currently controversially discussed. Some studies have suggested that LG72 binds to and regulates the activity of the peroxisomal enzyme D-amino-acid-oxidase, while others proposed an alternative role of this protein due to its mitochondrial location in vitro. Studies with transgenic mice expressing LG72 further suggested that high levels of LG72 lead to an impairment of mitochondrial functions with a concomitant increase in reactive oxygen species production. In the present study, we now performed extensive interaction analyses and identified the mitochondrial methionine-R-sulfoxide reductase B2 (MSRB2) as a specific interaction partner of LG72. MSRB2 belongs to the MSR protein family and functions in mitochondrial oxidative stress defense. Based on our results, we propose that LG72 is involved in the regulation of mitochondrial oxidative stress

Hsp70 chaperones: Cellular functions and molecular mechanism

Hsp70 proteins are central components of the cellular network of molecular chaperones and folding catalysts. They assist a large variety of protein folding processes in the cell by transient association of their substrate binding domain with short hydrophobic peptide segments within their substrate proteins. The substrate binding and release cycle is driven by the switching of Hsp70 between the low-affinity ATP bound state and the high-affinity ADP bound state. Thus, ATP binding and hydrolysis are essential in vitro and in vivo for the chaperone activity of Hsp70 proteins. This ATPase cycle is controlled by co-chaperones of the family of J-domain proteins, which target Hsp70s to their substrates, and by nucleotide exchange factors, which determine the lifetime of the Hsp70-substrate complex. Additional co-chaperones fine-tune this chaperone cycle. For specific tasks the Hsp70 cycle is coupled to the action of other chaperones, such as Hsp90 and Hsp100

The Hsc/Hsp70 Co-Chaperone Network Controls Antigen Aggregation and Presentation during Maturation of Professional Antigen Presenting Cells

The maturation of mouse macrophages and dendritic cells involves the transient deposition of ubiquitylated proteins in the form of dendritic cell aggresome-like induced structures (DALIS). Transient DALIS formation was used here as a paradigm to study how mammalian cells influence the formation and disassembly of protein aggregates through alterations of their proteostasis machinery. Co-chaperones that modulate the interplay of Hsc70 and Hsp70 with the ubiquitin-proteasome system (UPS) and the autophagosome-lysosome pathway emerged as key regulators of this process. The chaperone-associated ubiquitin ligase CHIP and the ubiquitin-domain protein BAG-1 are essential for DALIS formation in mouse macrophages and bone-marrow derived dendritic cells (BMDCs). CHIP also cooperates with BAG-3 and the autophagic ubiquitin adaptor p62 in the clearance of DALIS through chaperone-assisted selective autophagy (CASA). On the other hand, the co-chaperone HspBP1 inhibits the activity of CHIP and thereby attenuates antigen sequestration. Through a modulation of DALIS formation CHIP, BAG-1 and HspBP1 alter MHC class I mediated antigen presentation in mouse BMDCs. Our data show that the Hsc/Hsp70 co-chaperone network controls transient protein aggregation during maturation of professional antigen presenting cells and in this way regulates the immune response. Similar mechanisms may modulate the formation of aggresomes and aggresome-like induced structures (ALIS) in other mammalian cell types

The Convergence Behavior of the PBIL Algorithm: A Preliminary Approach

In this paper the simplest version of Population Based Incremental Learning (PBIL) is used to minimize the OneMax function in two dimensions. After carrying out several experiments to reveal the limit behavior of the algorithm in this function we obtain that the convergence results depend on the initial vector p (0) , and on the # parameter value. This experienced behavior is guaranteed for mathematical proof. The probability that the algorithm converges to any point of the search space goes to 1 when p (0) and # go to suitable values. Thus, even though the experimental results seem more stable when the # value is near to zero, we can not ensure that PBIL converges to the optimum. 1 Introduction During the nineties many real combinatorial optimization problems have been solved successfully using Genetic Algorithms (GAs). But the existence of deceptive problems where the performance of GAs is very poor have motivated the search for new optimization algorithms. To overcome these di..

PAS3, a Saccharomyces cerevisiae Gene Encoding a Peroxisomal Integral Membrane Protein Essential for Peroxisome Biogenesis

Saccharomyces cerevisiae pas3-mutants are described which conform the pas-phenotype recently reported for the peroxisomal assembly mutants pas1-1 and pas2. The isolation of pas3-mutants enabled us to clone the PAS3 gene by functional complementation. DNA sequence analysis revealed a 50.6-kD protein with at least one domain of sufficient length and hydrophobicity to span a lipid bilayer. To verify these predictions antibodies were raised against a truncated portion of the PAS3 coding region overexpressed in E. coli. Pas3p was identified as a 48 kD peroxisomal integral membrane protein. It is shown that a lack of this protein causes the peroxisome-deficient phenotype and the cytosolic mislocalization of peroxisomal matrix enzymes. Based on protease digestion experiments Pas3p is discussed to be anchored in the peroxisomal membrane by its amino-terminus while the bulk of the molecule is exposed to the cytosol. These findings are consistent with the possibility that Pas3p is one component of the peroxisomal import machinery.

Modulation of in vivo HSP70 chaperone activity by Hip and Bag-1

The chaperone activity of Hsp70 is influenced by the activities of both positive and negative regulatory proteins. In this study, we provide first time evidence for the stimulating effect of the Hsp70-interacting protein Hip on the chaperone activity in the mammalian cytosol. Overexpressing Hip enhances the refolding of the heat-inactivated reporter enzyme luciferase expressed in hamster lung fibroblasts. Also, it protects luciferase from irreversible denaturation under conditions of ATP depletion. We demonstrate that these stimulating actions depend on both the presence of the central Hsp70-binding site and the amino-terminal homo-oligomerization domain of Hip. The carboxyl terminus (amino acids 257-368) comprising the 7 GGMP repeats (Hsc70-like domain) and the Sti1p-like domain are dispensable for the Hip-mediated stimulation of the cellular chaperone activity. Bag-1, which inhibits the Hsp70 chaperone activity both in vitro and in vivo, was found to compete with the stimulatory action of Hip. In cells overexpressing both Hip and Bag-1, the inhibitory effects of Bag-1 were found to be dominant. Our results reveal that in vivo a complex level of regulation of the cellular chaperone activity exists that not only depends on the concentration of Hsp70 but also on the concentration, affinity, and intracellular localization of positive and negative coregulators. As the Hsp70 chaperone machine is also protective in the absence of ATP, our data also demonstrate that cycling between an ATP/ADP-bound state is not absolutely required for the Hsp70 chaperone machine to be active in vivo

Single-point mutation in a conserved TPR domain of Hip disrupts enhancement of glucocorticoid receptor signaling

The Hsp70-interacting protein Hip has been identified as a transient participant in the assembly of both glucocorticoid (GR) and progesterone receptor complexes. Although it has been difficult to identify a physiological role for Hip, it is believed to have intrinsic chaperoning properties and has been identified as a potential anti-apoptotic target of Granzyme B. In vitro assays have provided evidence that Hip may interact with GR complexes in an Hsp70 independent manner and can enhance the function of GR in hormone based reporter assays. In this study, a cDNA for human Hip was used in mutational analysis to map Hip function to critical structural elements. A single amino acid substitution (L211S) resulted in a loss of Hip function. This mutation also appears to disrupt the interaction of Hip with Hsp70 in vitro. Failure to recover Hip-L211S constructs in co-immunoprecipitation assays with an Hsp70 monoclonal antibody suggests that the mutation is unlikely to result in a misfolded substrate