[Ribosome and the secret of longevity]. / Ribosoma i sekret dolgoletiia.

Proteins in cells are constantly undergoing damage. Nevertheless, the concentration of damaged proteins in young organisms is maintained at the low level due to the continual protein turnover: degradation of damaged proteins and synthesis of new ones. During aging, the concentration of damaged proteins increases because of decelerating protein turnover, the cause of which is unknown, however, it may be related to the decrease in ribosome concentration.

[Novel type of signaling molecules: protein kinases covalently linked to ion channels]. / Signal'nye molekuly novogo tipa: proteinkinazy, kovalentno sviazannye s ionnymi kanalami.

Recently we identified a new class of protein kinases with a novel type of catalytic domain structurally and evolutionarily unrelated to the conventional eukaryotic protein kinases. This new class, which we named alpha-kinases, is represented by eukaryotic elongation factor-2 kinase and the Dictyostelium myosin heavy chain kinases. Here we cloned, sequenced and analyzed the tissue distribution of five new putative mammalian alpha-kinases: melanoma alpha-kinase, kidney alpha-kinase, heart alpha-kinase, skeletal muscle alpha-kinase, and lymphocyte alpha-kinase. All five are large proteins of more than 1000 amino acids with an alpha-kinase catalytic domain located at the very carboxyl-terminus. We expressed the catalytic domain of melanoma alpha-kinase in Escherichia coli, and found that it autophosphorylates on threonine residues, demonstrating that it is a genuine protein kinase. Unexpectedly, we found that the long amino-terminal portions of melanoma and kidney alpha-kinases represent new members of the transient receptor potential (TRP) ion channel family, which are implicated in the mediation of capacitative Ca2+ entry in nonexcitable mammalian cells. This suggests that melanoma and kidney alpha-kinases, which represent a novel type of signaling molecule, are involved in the regulation of Ca2+ influx in mammalian cells.

[Organization of enzymes on subcellular structures: relay at the surface]. / Organizatsiia fermentov na vnutrikletochnykh strukturakh: éstafeta u poverkhnosti.

There is a large body of evidence that soluble cytoplasmic enzymes of eukaryotic cells, e.g., glycolytic enzymes and proteins of the translational machinery, are organized in some way in space and in time. The following features of such organization emerge from the experimental data: (1) metabolites are transferred between enzymes directly "from hand to hand" in short-living enzyme-enzyme complexes rather than by diffusion in aqueous media; (2) enzymes show a tendency to be absorbed on surfaces of subcellular structures, such as membranes, cytoskeleton and polyribosomes; (3) enzymes are desorbed from a surface of a subcellular structure after binding specific metabolites, i.e., substrates and/or products of the reactions catalyzed by these enzymes. These features are suggestive of a relay mechanism for the enzyme systems functioning in a cell; an enzyme adsorbed on a surface of a subcellular structure is desorbed after binding its substrate or in the course of the catalytic act. Within a complex with its product the enzyme diffuses into the environment, until it reaches the next enzyme adsorbed on the same surface; then a short-living enzyme-enzyme complex is formed, and a direct "from hand to hand" transfer of the metabolite takes place. As a result, the overall metabolic process appears to be localized near the surface. We termed this mechanism as a "relay at the surface".

[Threonyl-tRNA synthase from rabbit reticulocytes: a reversible transition from the RNA-non-binding to the RNA-binding form]. / Treonil-tRNK-sintetaza retikulotsitov krolika: obratimyi perekhod iz RNK-nesviazyvaiushchei v RNK-sviazyvaiushchuiu formu.

A simple three-step procedure was used to isolate threonyl-tRNA synthetase of rabbit reticulocytes which is in a ribosome-free extract in the RNA-non-binding form. According to SDS electrophoresis, the enzyme has a molecular weight of 86 000 Da and is heterogeneous by isoelectric point; pI of the major component is near 6.2. Threonyl-tRNA synthetase is capable of interacting with a high molecular weight RNA (E. coli rRNA). Thus, in the course of purification threonyl-tRNA synthetase passes from the RNA-non-binding to the RNA-binding form. This transition was shown to be reversible.