Biomedical subjects

A Orlova

Publications and source records attributed to A Orlova.

23 records · Page 2Linked to original sources

PubMed1994

Three-dimensional reconstruction of a co-complex of F-actin with antibody Fab fragments to actin's NH2 terminus.

We have decorated F-actin with Fab fragments of antibodies to actin residues 1-7. These antibody fragments do not strongly affect the rigor binding of myosin S-1 to actin, but do affect the binding of S-1 to actin in the presence of nucleotide (DasGupta, G., and E. Reisler, 1989. J. Mol. Biol. 207:833-836; 1991. Biochemistry. 30:9961-9966; 1992. Biochemistry. 31:1836-1841). Although the binding constant is rather low, we estimate that we have achieved about 85% occupancy of the actin sites. Three-dimensional reconstructions from electron micrographs of both negatively stained and frozen-hydrated filaments show that the Fab fragment is bound at the location of the NH2 terminus in the model of Holmes et al. (Holmes, K.C., D. Popp, W. Gebhard, and W. Kabsch. 1990. Nature. 347:37-44) for F-actin, excluding very different orientations of the actin subunit in the filament. Most of the mass of the antibody is not visualized, which is due to the large mobility of the NH2 terminus in F-actin, differences in binding angle within the polyclonal antibody population, or a combination of both of these possibilities.

Actins↗

PubMed1993

A conformational change in the actin subunit can change the flexibility of the actin filament.

The mechanical properties of F-actin are very significant, given the central structural role played by actin filaments within muscle and the cytoskeleton. We have determined that actin can exist in a state that has a fourfold increase in flexibility over normal F-actin, and nucleotide. Three-dimensional reconstructions from electron micrographs suggest that this increased flexibility arises from a rotation of subdomain-2, the smallest subdomain, of the actin subunit. The modulation of actin's flexibility by Ca2+ and Mg2+ may have important physiological consequences within the cell. Further, since it has been shown that myosin-decorated actin filaments are more flexible than pure F-actin, it is possible that myosin induces this more flexible state in actin.

Actin Cytoskeleton↗

PubMed1992

Structural basis for the destabilization of F-actin by phosphate release following ATP hydrolysis.

The role of ATP hydrolysis in actin polymerization has been a puzzle, since it is known that polymer formation is possible without the ATPase activity and that the ATPase lags behind polymerization. We have used beryllium fluoride and G-ADP actin monomers to form F-ADP-BeF3- filaments that are a stable analog for either the ATP or the ADP-P(i) state. Electron microscopy and computed three-dimensional reconstruction have been used to compare this state to control actin, F-ADP, polymerized from G-ATP. We find, at a high degree of statistical significance, that subdomain-2 of the actin protomer in the ADP-BeF3- state is in a conformation very similar to that found in the atomic model for F-actin of Holmes and co-workers, but becomes disordered after the release of the phosphate. This breaks one of the longitudinal bonds in the filament, consistent with biochemical observations that phosphate release destabilizes F-actin. We have also found that lithium, which reduces the dissociation rate constant of actin filaments, induces a structural state indistinguishable from that of ADP-BeF3-. Further, in all states about ten C-terminal residues are displaced from the above mentioned model, but that the fit of the rest of the monomer is in excellent agreement, supporting the uniqueness of the solution they found and precluding a significantly different arrangement of the actin monomer in the filament.

Actins↗

PubMedDate not supplied

Allostery, cooperativity, and different structural states in F-actin.

Electron microscopy and three-dimensional reconstructions have been used to show that F-actin can exist in multiple states. We have also been able to visualize large allosteric effects involving the C-terminus, the nucleotide binding site, the high-affinity metal-binding site, and the DNase I-binding loop. Further, there exists a large degree of cooper-activity in F-actin, such that conformational changes at one end of a filament may be transmitted to the other, distant, end. While many of these allosteric and cooperative effects have been previously suggested to exist based upon biochemical observations, we have been able to observe that these effects probably involve the movement of a large number of residues over significant distances. In systems such as muscle some of these conformational changes in F-actin may play an important role.

Actins↗

PubMedDate not supplied

Closo-dodecaborate(2-) as a linker for iodination of macromolecules. Aspects on conjugation chemistry and biodistribution.

Boron-containing compounds like closo-dodecaborate(2-) are in theory suitable for radioactive labeling with halogens. The boron-halogen bond is stronger than carbon-halogen bond and is not likely to be recognized by deiodinating enzymes in vivo. Peptides and proteins may be conjugated with various closo-dodecaborate(2-)-containing ligands, and thereafter, the conjugate can be iodinated. Since closo-dodecaborate(2-) is more avidly iodinated than tyrosine in moderately acidic media, such conjugates may be directly labeled on the boron part with radioisotopes of iodine using the standard Chloramine-T procedure. Mercapto-undecahydro-closo-dodecaborate(2-) (BSH) was reacted with the double bond of allyldextran to form a boronated dextran compound of the molecular size of about 70 kDa. This compound, in the text denoted as Dx-BS, and cesium dodecahydro-closo-dodecaborate(2-) were labeled using iodine-125. The two compounds were administered to rats in order to study their in vivo stability. The results indicate that iodinated Dx-BS is stable for about 20 h in vivo. The degradation rate, as indicated by thyroid uptake, was found low. [125I]Iodo-closo-dodecaborate(2-), which is a possible degradation product of [125I]Dx-BS-I, was rapidly excreted in urine without significant accumulation in any organ.

Animals↗