Biomedical subjects

S Falke

Publications and source records attributed to S Falke.

4 recordsLinked to original sources

PubMed2001

Structural changes in GroEL effected by binding a denatured protein substrate.

In the absence of nucleotides or cofactors, the Escherichia coli chaperonin GroEL binds select proteins in non-native conformations, such as denatured glutamine synthetase (GS) monomers, preventing their aggregation and spontaneous renaturation. The nature of the GroEL-GS complexes thus formed, specifically the effect on the conformation of the GroEL tetradecamer, has been examined by electron microscopy. We find that specimens of GroEL-GS are visibly heterogeneous, due to incomplete loading of GroEL with GS. Images contain particles indistinguishable from GroEL alone, and also those with consistent identifiable differences. Side-views of the modified particles reveal additional protein density at one end of the GroEL-GS complex, and end-views display chirality in the heptameric projection not seen in the unliganded GroEL. The coordinate appearance of these two projection differences suggests that binding of GS, as representative of a class of protein substrates, induces or stabilizes a conformation of GroEL that differs from the unliganded chaperonin. Three-dimensional reconstruction of the GroEL-GS complex reveals the location of the bound protein substrate, as well as complex conformational changes in GroEL itself, both cis and trans with respect to the bound GS. The most apparent structural alterations are inward movements of the apical domains of both GroEL heptamers, protrusion of the substrate protein from the cavity of the cis ring, and a narrowing of the unoccupied opening of the trans ring.

Chaperonin 60↗

PubMed1997

Structural and functional effects of PA700 and modulator protein on proteasomes.

Control and targeting of the proteolytic activity of the major intracellular protease, the proteasome, is accomplished by various regulatory protein complexes that may form higher-order assemblies with the proteasome. An activator of proteolytic activity, PA700, has been shown to have an ATP-dependent stimulatory effect on the peptidase activities of the proteasome, and another protein factor, the modulator, further enhances the effect of PA700. Here we show that the addition of PA700 endows the proteasome with the ability to cleave ubiquitinated proteins, a property associated with the previously isolated 26 S form of the proteasome. The modulator further stimulates this specific activity, without having any such effect on the proteasome alone. Using electron microscopy, we show that addition of PA700 causes the appearance of protein "caps" at one or both ends of proteasomes, forming structures that are indistinguishable from 26 S proteasomes. Quantitation of the numbers of uncapped, singly capped and doubly capped complexes indicates cooperativity in the association of PA700 with the two ends of the proteasome. Addition of modulator protein makes no further structural modification that is detectable by electron microscopy, but does cause an increase in the number of capped complexes visible at subsaturating concentrations of PA700. Hence PA700 converts the proteasome both functionally and structurally to the 26 S form, and the modulator promotes this transformation, apparently without stable association with the resulting complex.

Adenosine Triphosphate↗

PubMedDate not supplied

Classification and reconstruction of a heterogeneous set of electron microscopic images: a case study of GroEL-substrate complexes.

Image analysis methods were used to separate images of a large macromolecular complex, the chaperonin GroEL, in a preparation in which it is partially liganded to a nonnative protein substrate, glutamine synthetase. The relatively small difference ( approximately 6%) in size between the chaperonin in its free and complexed forms, and the absence of gross changes in overall conformation, made separation of the two types of particles challenging. Different approaches were evaluated and used for alignment and classification of images, both in two common projections and in three dimensions, yielding 2D averages and a 3D reconstruction. The results of 3D analysis describe the conformational changes effected by binding of this particular protein substrate and demonstrate the utility of 2D analysis as an indicator of structural change in this system.

Chaperonin 60↗

PubMedDate not supplied

[The induction of an acquired storage pool deficiency of the thrombocytes by IgG antibodies in systemic lupus erythematosus and chronic polyarthritis].

Sera of patients with RA and SLE contain platelet-reactive IgG antibodies, which bring about the release of serotonin from platelets. They can also induce the aggregation of normal human platelets. In addition, such antibodies cause a decreased in vitro disaggregation of platelets after ADP exposure, as well as a significantly reduced collagen-induced aggregation. Thus, IgG platelet antibodies in RA and SLE can cause a functional impairment of patients' platelets, and may also be instrumental in systemic inflammatory rheumatoid disease by releasing proinflammatory mediators.

Adenosine Diphosphate↗