[Effect of mutations imitating the phosphorylation by TRPM7 kinase on the function of the N-terminal domain of tropomodulin].

It has been shown that tropomodulin 1 is phosphorylated at serine and threonine residues by TRPM7 kinase. The phosphorylation sites for TRPM7 kinase in the N-terminal functional domain of tropomodulin 1 have been identified, which include tropomyosin-binding and actin-capping regions. It has been found that the phosphorylation-mimicking mutation T54E resulted in the loss of the capping ability of the N-terminal tropomodulin domain; however, its tropomyosin-binding ability did not change. We further hypothesize that the phosphorylation of tropomodulin by TRPM7 kinase may play a role in the regulation of the dynamics of actin filaments.

[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.

Identification of a new class of protein kinases represented by eukaryotic elongation factor-2 kinase.

The several hundred members of the eukaryotic protein kinase superfamily characterized to date share a similar catalytic domain structure, consisting of 12 conserved subdomains. Here we report the existence and wide occurrence in eukaryotes of a protein kinase with a completely different structure. We cloned and sequenced the human, mouse, rat, and Caenorhabditis elegans eukaryotic elongation factor-2 kinase (eEF-2 kinase) and found that with the exception of the ATP-binding site, they do not contain any sequence motifs characteristic of the eukaryotic protein kinase superfamily. Comparison of different eEF-2 kinase sequences reveals a highly conserved region of approximately 200 amino acids which was found to be homologous to the catalytic domain of the recently described myosin heavy chain kinase A (MHCK A) from Dictyostelium. This suggests that eEF-2 kinase and MHCK A are members of a new class of protein kinases with a novel catalytic domain structure.