Computer-aided design of a PDZ domain to recognize new target sequences

PDZ domains are small globular domains that recognize the last 4-7 amino acids at the C-terminus of target proteins. The specificity of the PDZ-ligand recognition is due to side chain-side chain interactions, as well as the positioning of an alpha-helix involved in ligand binding. We have used computer-aided protein design to produce mutant versions of a Class I PDZ domain that bind to novel Class I and Class II target sequences both in vitro and in vivo, thus providing an alternative to primary antibodies in western blotting, affinity chromatography and pull-down experiments. Our results suggest that by combining different backbone templates with computer-aided protein design, PDZ domains could be engineered to specifically recognize a large number of proteins.     

Regulation of myocardial contractility and cell size by distinct PI3K-PTEN signaling pathways

The PTEN/PI3K signaling pathway regulates a vast array of fundamental cellular responses. We show that cardiomyocyte-specific inactivation of tumor suppressor PTEN results in hypertrophy, and unexpectedly, a dramatic decrease in cardiac contractility. Analysis of double-mutant mice revealed that the cardiac hypertrophy and the contractility defects could be genetically uncoupled. PI3Kalpha mediates the alteration in cell size while PI3Kgamma acts as a negative regulator of cardiac contractility. Mechanistically, PI3Kgamma inhibits cAMP production and hypercontractility can be reverted by blocking cAMP function. These data show that PTEN has an important in vivo role in cardiomyocyte hypertrophy and GPCR signaling and identify a function for the PTEN-PI3Kgamma pathway in the modulation of heart muscle contractility.     

Principles of creating biotransducers based on nucleic acid liquid crystals

A brief concept of biosensors is presented. Structural peculiarities and properties of single- and double-stranded nucleic acids that are to be taken into account when creating sensing units for biosensors using different principles of molecular recognition are considered. General schemes of sensing units based on liquid-crystalline dispersions formed from low-molecular mass DNA, its complexes with "cross-linking" agents and from circular superhelical DNA molecules are described.     

Substrate access to the active sites in aminopeptidase T, a representative of a new metallopeptidase clan

Aminopeptidase T (AmpT) from Thermus thermophilus is a metalloexopeptidase with no similarity to prototypical metallopeptidases with an HExxH or HxxEH motif. The crystal structure of the Staphylococcus aureus homologue of AmpT, which is known as aminopeptidase S (AmpS), has been reported recently. This structure revealed a dimeric protein with a very unusual, elongated shape and a large internal cavity. The active sites were found on the inner walls of the cavity and were entirely shielded from the environment, which suggested either that the dimer in the crystals was not physiologically relevant, or that an inactive conformation had been crystallized. Here, we show by gel-filtration and analytical ultracentrifugation that AmpT, like AmpS, forms dimers in solution, and we present the structure of AmpT in a crystal form with five protomers in the asymmetric unit. The five protomers take conformations that range from fully closed, as in the AmpS structure, to nearly open, so that the active site is almost directly accessible. The different conformations indicate flexibility between the AmpT N and C-domains, and explain how AmpT can be active, although the unusual AmpS dimerization mode applies to AmpT as well.     

ATP-dependent membrane assembly of F-actin facilitates membrane fusion

We recently established an in vitro assay that monitors the fusion between latex-bead phagosomes and endocytic organelles in the presence of J774 macrophage cytosol (). Here, we show that different reagents affecting the actin cytoskeleton can either inhibit or stimulate this fusion process. Because the membranes of purified phagosomes can assemble F-actin de novo from pure actin with ATP (), we focused here on the ability of membranes to nucleate actin in the presence of J774 cytosolic extracts. For this, we used F-actin sedimentation, pyrene actin assays, and torsional rheometry, a biophysical approach that could provide kinetic information on actin polymerization and gel formation. We make two major conclusions. First, under our standard in vitro conditions (4 mg/ml cytosol and 1 mM ATP), the presence of membranes actively catalyzed the assembly of cytosolic F-actin, which assembled into highly viscoelastic gels. A model is discussed that links these results to how the actin may facilitate fusion. Second, cytosolic actin paradoxically polymerized more under ATP depletion than under high-ATP conditions, even in the absence of membranes; we discuss these data in the context of the well described, large increases in F-actin seen in many cells during ischemia.     

Histamine and bradykinin stimulate the phosphoinositide turnover in human umbilical vein endothelial cells via different G-proteins

The G-proteins which regulate hormonal turnover of phosphoinositide (PI) in human umbilical vein endothelial cells have been investigated. A 40-41 kDa doublet present in the membranes of these cells was selectively ADP ribosylated by pertussis toxin (PTx), and this doublet was Gi alpha 2 and Gi alpha 3 according to immunoblotting with specific antisera. By contrast, a doublet of 24-26 kDa proteins in the same membrane preparations was ADP ribosylated by the C3 component of botulinum toxin (BoTx). PTx-dependent ADP ribosylation blocked stimulation of PI turnover by histamine, but did not affect stimulation by bradykinin, whereas BoTx (C2 + C3 components) had the opposite effect. Thus two different groups of G-proteins may be involved in hormone-dependent stimulation of PI turnover in human umbilical vein endothelial cells.     

Crystal structure of human filamin C domain 23 and small angle scattering model for filamin C 23-24 dimer

Filamin C is a dimeric, actin-binding protein involved in organization of cortical cytoskeleton and of the sarcomere. We performed crystallographic, small-angle X-ray scattering and analytical ultracentrifugation experiments on the constructs containing carboxy-terminal domains of the protein (domains 23-24 and 19-21). The crystal structure of domain 23 of filamin C showed that the protein adopts the expected immunoglobulin (Ig)-like fold. Small-angle X-ray scattering experiments performed on filamin C tandem Ig-like domains 23 and 24 reveal a dimer that is formed by domain 24 and that domain 23 has little interactions with itself or with domain 24, while the analytical ultracentrifugation experiments showed that the filamin C domains 19-21 form elongated monomers in diluted solutions.     

Tyrosine phosphorylation modifies protein kinase C delta-dependent phosphorylation of cardiac troponin I

Our study identifies tyrosine phosphorylation as a novel protein kinase Cdelta (PKCdelta) activation mechanism that modifies PKCdelta-dependent phosphorylation of cardiac troponin I (cTnI), a myofilament regulatory protein. PKCdelta phosphorylates cTnI at Ser23/Ser24 when activated by lipid cofactors; Src phosphorylates PKCdelta at Tyr311 and Tyr332 leading to enhanced PKCdelta autophosphorylation at Thr505 (its activation loop) and PKCdelta-dependent cTnI phosphorylation at both Ser23/Ser24 and Thr144. The Src-dependent acquisition of cTnI-Thr144 kinase activity is abrogated by Y311F or T505A substitutions. Treatment of detergent-extracted single cardiomyocytes with lipid-activated PKCdelta induces depressed tension at submaximum but not maximum [Ca2+] as expected for cTnI-Ser23/Ser24 phosphorylation. Treatment of myocytes with Src-activated PKCdelta leads to depressed maximum tension and cross-bridge kinetics, attributable to a dominant effect of cTnI-Thr144 phosphorylation. Our data implicate PKCdelta-Tyr311/Thr505 phosphorylation as dynamically regulated modifications that alter PKCdelta enzymology and allow for stimulus-specific control of cardiac mechanics during growth factor stimulation and oxidative stress.     

Evaluation of influenza vaccine Vaxigrip in the combined immunization of conscripts during influenza seasons of 2002-2003

The immunization properties of the influenza vaccine Vaxigrip, used in combination with vaccines against pneunococcal infection and hepatitis A (respectively, Pneumo 23 and Avaxim), were evaluated. In Central Russia in one of the units of the internal forces of the RF Ministry of Internal Affairs 3 groups totaling 755 servicemen were formed, depending on the complex of the introduced vaccines. Active medical observation and the registration of the complaints of the vaccinees at the postvaccinal period did not reveal unusual reactions and complications in none of the groups under observation. In the evaluation of the level of specific antibodies to the circulating influenza viruses prior to vaccination the low level of collective protection to influenza B virus was determined: protective antibody levels were registered only in 14-18% of the servicemen, while the corresponding data with respect of influenza viruses A(H1N1) and A(H3N2) were 45-50% and 56-63% respectively. At the same time, in seronegative persons the vaccine Vaxigrip exhibited high immunogenic activity with respect of all 3 influenza strains; seroconversion to them was determined in 84-92% of the vaccines, and the level of protective antibody titers before the beginning of the epidemic season was 86-99% in the whole of the group. The characteristics of the prophylactic effectiveness of the vaccine Vaxigrip in relation to the influenza virus infection level 1 were 4.7 (index) and 79% (coefficient). In addition, the frequency of influenza cases, clinically pronounced and confirmed by laboratory methods, in patients who had been immunized with 3 vaccines was 6.7%, which was 10.3 times less frequent than number of cases in the groups of comparison (68.2% on the average). The coefficient of epidemiological effectiveness of the prophylaxis of influenza was 90.2%. The complex use of 3 preparations did not affect the immunization properties of the vaccine Vaxigrip.     

Caveolae-associated proteins in cardiomyocytes: caveolin-2 expression and interactions with caveolin-3

Caveolin-3 the muscle-specific caveolin isoform, acts like the more ubiquitously expressed caveolin-1 to sculpt caveolae, specialized membrane microdomains that serve as platforms to organize signal transduction pathways. Caveolin-2 is a structurally related isoform that alone does not drive caveolae biogenesis; rather, caveolin-2 cooperates with caveolin-1 to form caveolae in nonmuscle cells. Although caveolin-2 might be expected to interact in an fashion analogous to that of caveolin-3, it generally has not been detected in cardiomyocytes. This study shows that caveolin-2 and caveolin-3 are detected at low levels in ventricular myocardium and increase dramatically with age or when neonatal cardiomyocytes are placed in culture. In contrast, flotillins (caveolin functional homologs) are expressed at relatively constant levels in these preparations. In neonatal cardiac cultures, caveolin-2 and -3 expression is not influenced by thyroid hormone (a postnatal regulator of other cardiac gene products). The further evidence that caveolin-2 coimmunoprecipitates with caveolin-3 and floats with caveolin-3 by isopycnic centrifugation in cardiomyocyte cultures suggests that caveolin-2 may play a role in caveolae biogenesis and influence cardiac muscle physiology.