The control of spindle length by Hsp70 and Hsp110 molecular chaperones

AbstractMolecular chaperones are an essential group of proteins required to maintain proper protein homeostasis in the cell and include Hsp40, Hsp60, Hsp70, Hsp90, and Hsp100 among others. Hsp110 proteins form a subfamily of the Hsp70 family and seem to primarily function as nucleotide exchange factors for the Hsp70s. Data to date suggest that Hsp110 together with Hsp70 are required to ensure proper spindle assembly and nuclear distribution during cell division. More specifically, we propose that an Hsp110–Hsp70 complex modulates the activity and directionality of the kinesin-5 motor, Cin8, which is required for spindle elongation. The modulation of spindle length by molecular chaperones might be a mechanism by which cell division can be controlled especially under proteostatic stress

The AAA+ superfamily of functionally diverse proteins

The AAA+ superfamily is a large superfamily of ATPases that are characterized by a conserved catalytic module, the AAA+ module. Members are involved in an astonishing range of different cellular processes

The RavA-ViaA Chaperone-Like System Interacts with and Modulates the Activity of the Fumarate Reductase Respiratory Complex

Regulatory ATPase variant A (RavA) is a MoxR AAA + protein that functions together with a partner protein that we termed VWA interacting with AAA + ATPase (ViaA) containing a von Willebrand Factor A domain. However, the functional role of RavA-ViaA in the cell is not yet well established. Here, we show that RavA-ViaA are functionally associated with anaerobic respiration in Escherichia coli through interactions with the fumarate reductase (Frd) electron transport complex. Expression analysis of ravA and viaA genes showed that both proteins are co-expressed with multiple anaerobic respiratory genes, many of which are regulated by the anaerobic transcriptional regulator Fnr. Consistently, the expression of both ravA and viaA was found to be dependent on Fnr in cells grown under oxygen-limiting condition. ViaA was found to physically interact with FrdA, the flavin-containing subunit of the Frd complex. Both RavA and the Fe–S-containing subunit of the Frd complex, FrdB, regulate this interaction. Importantly, Frd activity was observed to increase in the absence of RavA and ViaA. This indicates that RavA and ViaA modulate the activity of the Frd complex, signifying a potential regulatory chaperone-like function for RavA-ViaA during bacterial anaerobic respiration with fumarate as the terminal electron acceptor

In Vivo Observation of Polypeptide Flux through the Bacterial Chaperonin System

AbstractThe quantitative contribution of chaperonin GroEL to protein folding in E. coli was analyzed. A diverse set of newly synthesized polypeptides, predominantly between 10–55 kDa, interacts with GroEL, accounting for 10%–15% of all cytoplasmic protein under normal growth conditions, and for 30% or more upon exposure to heat stress. Most proteins leave GroEL rapidly within 10–30 s. We distinguish three classes of substrate proteins: (I) proteins with a chaperonin-independent folding pathway; (II) proteins, more than 50% of total, with an intermediate chaperonin dependence for which normally only a small fraction transits GroEL; and (III) a set of highly chaperonin-dependent proteins, many of which dissociate slowly from GroEL and probably require sequestration of aggregation-sensitive intermediates within the GroEL cavity for successful folding

Tamoxifen Enhances the Hsp90 Molecular Chaperone ATPase Activity

Background: Hsp90 is an essential molecular chaperone that is also a novel anti-cancer drug target. There is growing interest in developing new drugs that modulate Hsp90 activity. Methodology/Principal Findings: Using a virtual screening approach, 4-hydroxytamoxifen, the active metabolite of the anti-estrogen drug tamoxifen, was identified as a putative Hsp90 ligand. Surprisingly, while all drugs targeting Hsp90 inhibit the chaperone ATPase activity, it was found experimentally that 4-hydroxytamoxifen and tamoxifen enhance rather than inhibit Hsp90 ATPase. Conclusions/Significance: Hence, tamoxifen and its metabolite are the first members of a new pharmacological class of Hsp90 activators

Identifying Predictors of High Sodium Excretion in Patients with Heart Failure: A Mixed Effect Analysis of Longitudinal Data

BACKGROUND: A low-sodium diet is a core component of heart failure self-care but patients have difficulty following the diet. AIM: The aim of this study was to identify predictors of higher than recommended sodium excretion among patients with heart failure. METHODS: The World Health Organization Five Dimensions of Adherence model was used to guide analysis of existing data collected from a prospective, longitudinal study of 280 community-dwelling adults with previously or currently symptomatic heart failure. Sodium excretion was measured objectively using 24-hour urine sodium measured at three time points over six months. A mixed effect logistic model identified predictors of higher than recommended sodium excretion. RESULTS: The adjusted odds of higher sodium excretion were 2.90, (95% confidence interval (CI): 1.15-4.25, pp=0.007) for patients with diabetes; and 2.22 (95% CI: 1.09-4.53, p=0.028) for patients who were cognitively intact. CONCLUSION: Three factors were associated with excess sodium excretion and two factors, obesity and diabetes, are modifiable by changing dietary food patterns

High-spin structures of 136Cs

Odd-odd 136Cs nuclei have been produced in the 18O + 208Pb and 12C + 238U fusion-fission reactions and their gamma rays studied with the Euroball array. The high-spin level scheme has been built up to ~ 4.7 MeV excitation energy and spin I ~ 16 hbar from the triple gamma-ray coincidence data. The configurations of the three structures observed above ~ 2 MeV excitation energy are first discussed by analogy with the proton excitations identified in the semi-magic 137Cs nucleus, which involve the three high-j orbits lying above the Z=50 gap, pi g_{7/2}, pi d_{5/2} and pi h_{11/2}. This is confirmed by the results of shell-model calculations performed in this work.Comment: 6 pages, 4 figures, 3 table