Synergistic cooperation between two ClpB isoforms in aggregate reactivation.

Bacterial AAA+ ATPase ClpB cooperates with DnaK during reactivation of aggregated proteins. The ClpB-mediated disaggregation is linked to translocation of polypeptides through the channel in the oligomeric ClpB. Two isoforms of ClpB are produced in vivo: the full-length ClpB95 and ClpB80, which does not contain the substrate-interacting N-terminal domain.

Protein kinase C as a stress sensor.

While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart.

Human serum albumin nanoparticles for efficient delivery of Cu, Zn superoxide dismutase gene.

Purpose: To assess the potential of human serum albumin nanoparticles (HSA NP) as a nonviral vector for ocular delivery of Cu, Zn superoxide dismutase (SOD1) gene.

Methods: Cu, Zn superoxide dismutase (SOD1) gene-encapsulated nanoparticles (NP) were developed using human serum albumin (HSA), an endogenous protein, by a desolvation-crosslinking method. The pSOD-loaded HSA NP was evaluated for in vitro release characteristics, stability against DNase I and vitreous humor degradation, cytotoxicity, cellular uptake mechanisms, in vitro transfection efficiency, and in vivo gene expression.

The amino-terminal domain of ClpB supports binding to strongly aggregated proteins.

Bacterial heat-shock proteins, ClpB and DnaK form a bichaperone system that efficiently reactivates aggregated proteins. ClpB undergoes nucleotide-dependent self-association and forms ring-shaped oligomers. The ClpB-assisted dissociation of protein aggregates is linked to translocation of substrates through the central channel in the oligomeric ClpB.

The N-terminal domain of Escherichia coli ClpB enhances chaperone function.

ClpB/Hsp104 collaborates with the Hsp70 system to promote the solubilization and reactivation of proteins that misfold and aggregate following heat shock. In Escherichia coli and other eubacteria, two ClpB isoforms (ClpB95 and ClpB80) that differ by the presence or absence of a highly mobile 149-residues long N-terminus domain are synthesized from the same transcript. Whether and how the N-domain contributes to ClpB chaperone activity remains controversial.

Nucleotide-induced switch in oligomerization of the AAA+ ATPase ClpB.

ClpB is a member of the bacterial protein-disaggregating chaperone machinery and belongs to the AAA(+) superfamily of ATPases associated with various cellular activities. The mechanism of ClpB-assisted reactivation of strongly aggregated proteins is unknown and the oligomeric state of ClpB has been under discussion. Sedimentation equilibrium and sedimentation velocity show that, under physiological ionic strength in the absence of nucleotides, ClpB from Escherichia coli undergoes reversible self-association that involves protein concentration-dependent populations of monomers, heptamers, and intermediate-size oligomers.

Structure and function of the middle domain of ClpB from Escherichia coli.

ClpB belongs to the Hsp100/Clp ATPase family. Whereas a homologue of ClpB, ClpA, interacts with and stimulates the peptidase ClpP, ClpB does not associate with peptidases and instead cooperates with DnaK/DnaJ/GrpE in an efficient reactivation of severely aggregated proteins. The major difference between ClpA and ClpB is located in the middle sequence region (MD) that is much longer in ClpB than in ClpA and contains several segments of coiled-coil-like heptad repeats.

Site-directed mutagenesis of conserved charged amino acid residues in ClpB from Escherichia coli.

ClpB is a member of a multichaperone system in Escherichia coli (with DnaK, DnaJ, and GrpE) that reactivates strongly aggregated proteins. The sequence of ClpB contains two ATP-binding domains, each containing Walker consensus motifs. The N- and C-terminal sequence regions of ClpB do not contain known functional motifs.