Co-translation folding, compartmentalization and modification of proteins

Transmembrane transport of polypeptide chains in the process of their synthesis on membrane-bound ribosomes and enzymic modification of the nascent polypeptides on membranes are reviewed. The possible role of ribosomes in protein folding and some other unsolved problems are discussed.     

Hepatitis C virus: The role of N-glycosylation sites of viral genotype 1b proteins for formation of viral particles in insect and mammalian cells

Hepatitis C virus (HCV) is characterized by considerable genetic variability and, as a consequence, it has 6 genotypes and multitude of subtypes. HCV envelope glycoproteins are involved in the virion formation; the correct folding of these proteins plays the key role in virus infectivity. Glycosylation at certain sites of different genotypes HCV glycoproteins shows substantial differences in functions of the individual glycans (Goffard et al., 2005; Helle et al., 2010) [1], [2]. In this study, differential glycosylation sites of HCV genotype 1b envelope proteins in insect and mammalian cells was demonstrated. We showed that part of glycosylation sites was important for folding of the proteins involved in the formation of viral particles. Point mutations were introduced in the protein N-glycosylation sites of HCV (genotype 1b) and the mutant proteins were analyzed using baculovirus expression system in mammalian and insect cells. Our data showed that, in contrast to HCV 1a and 2a, the folding of HCV 1b envelope proteins E2 (sites N1, N2, N10) and E1 (sites N1, N5) was disrupted, however that did not prevent the formation of virus-like particles (VLP) with misfolded glycoproteins having densities typical for HCV particles containing RNA fragments. Experimental data are supported by mathematical modeling of the structure of E1 mutant variants.     

Activated leukemic oncogenes responsible for neoplastic transformation of hematopoietic cells

Leukemias are a heterogeneous group of malignant blood diseases that are characterized by expansion of immature blast cells. The point molecular mechanisms of leukemogenesis are still unknown. Leukemia patients frequently have mutations of the genes responsible for normal proliferation and differentiation of hematopoietic stem cells. At present, scientific groups worldwide are engaged in biomedical studies of the structural and functional aspects of leukemic oncogenes and their role in human and animal leukemogenesis. The review describes the current concepts of the molecular properties of oncogenes whose activation may lead to CBF-AML, which results from mutations of the genes for the core binding factors AML1 (CBF6h) and CBFß.     

The emergence of molecular machines as a prerequisite of the ancient RNA world evolution

The problem of the start of biological evolution in the ancient RNA world is considered. It is postulated that the appearance of catalytic RNAs — ribozymes — via spontaneous cis- and trans-rearrangements of polyribonucleotides in primordial Darwin ponds should not have been sufficient for the start of evolution, until a new class of functional RNA, namely energy-dependent molecular machines, arose. The proposed hypothesis is that the simplest and primary type of molecular machines could be nucleoside triphosphate-dependent RNA-based helicases, which were capable of unwinding the stable double-helical RNAs inevitably formed during RNA syntheses on complementary templates. Thereupon, unwinding RNA polymerases could appear as a result of association or fusion of helicases and polyribonucleotide-polymerizing ribozymes. The latter event provided the mechanism of RNA replication using the double-helical RNAs as a communal genofond (gene pool) of a Darwin pond, and thus initiated the fast evolution of the ancient RNA world.     

Phosphorylation of elongation factor 2: a key mechanism regulating gene expression in vertebrates

Elongation factor 2 (eEF-2) is a 100-kD protein that catalyzes the ribosomal translocation reaction, resulting in the movement of ribosomes along mRNA. eEF-2 is the target for a very specific Ca2+/calmodulin-dependent eEF-2 kinase. Phosphorylation of eEF-2 makes it inactive in translation, which suggests that protein synthesis can be regulated by Ca2+ through eEF-2 phosphorylation. Recent data demonstrate that eEF-2 phosphorylation can be involved in cell-cycle regulation and other processes where changes of intracellular Ca2+ concentration induce a new physiological state of a cell. The main role of eEF-2 phosphorylation in these processes is temporary inhibition of overall translation in response to transient elevation of the Ca2+ concentrations in the cytoplasm. Temporary inhibition of translation may trigger the transition of a cell from one physiologic state into another because of the disappearance of short-lived repressors and thus the activation of expression of new genes.