3 research outputs found
MicroRNAs are exported from malignant cells in customized particles
MicroRNAs (miRNAs) are released from cells in association with proteins or microvesicles. We previously reported that malignant transformation changes the assortment of released miRNAs by affecting whether a particular miRNA species is released or retained by the cell. How this selectivity occurs is unclear. Here we report that selectively exported miRNAs, whose release is increased in malignant cells, are packaged in structures that are different from those that carry neutrally released miRNAs (n-miRNAs), whose release is not affected by malignancy. By separating breast cancer cell microvesicles, we find that selectively released miRNAs associate with exosomes and nucleosomes. However, n-miRNAs of breast cancer cells associate with unconventional exosomes, which are larger than conventional exosomes and enriched in CD44, a protein relevant to breast cancer metastasis. Based on their large size, we call these vesicles L-exosomes. Contrary to the distribution of miRNAs among different microvesicles of breast cancer cells, normal cells release all measured miRNAs in a single type of vesicle. Our results suggest that malignant transformation alters the pathways through which specific miRNAs are exported from cells. These changes in the particles and their miRNA cargo could be used to detect the presence of malignant cells in the body
Evolutionary Basis for the Coupled-domain Motions in Thermus thermophilus Leucyl-tRNA Synthetase*S⃞
Aminoacyl-tRNA synthetases are multidomain proteins that catalyze the
covalent attachment of amino acids to their cognate transfer RNA. Various
domains of an aminoacyl-tRNA synthetase perform their specific functions in a
highly coordinated manner to maintain high accuracy in protein synthesis in
cells. The coordination of their function, therefore, requires communication
between domains. In this study we explored the relevance of enzyme motion in
domain-domain communications. Specifically, we attempted to probe whether the
communication between distantly located domains of a multidomain protein is
accomplished through a coordinated movement of structural elements. We
investigated the collective motion in Thermus thermophilus
leucyl-tRNA synthetase by studying the low frequency normal modes. We
identified the mode that best described the experimentally observed
conformational changes of T. thermophilus leucyl-tRNA synthetase upon
substrate binding and analyzed the correlated and anticorrelated motions
between different domains. Furthermore, we used statistical coupling analysis
to explore if the amino acid pairs and/or clusters whose motions are thermally
coupled have also coevolved. Our study demonstrates that a small number of
residues belong to the category whose coupled thermal motions correspond to
evolutionary coupling as well. These residue clusters constitute a
distinguished set of interacting networks that are sparsely distributed in the
domain interface. Residues of these networking clusters are within van der
Waals contact, and we suggest that they are critical in the propagation of
long range mechanochemical motions in T. thermophilus leucyl-tRNA
synthetase