A Possible Role of Intracellular Isoelectric Focusing in the Evolution of Eukaryotic Cells and Multicellular Organisms

Abstract

A new scenario of the origin of eukaryotic cell and multicellularity is presented. A concentric pH-gradient has been shown to exist in the cytosol of eukaryotic cells. The most probable source of such gradient is its self-formation in gradient of electric field between center and periphery of a cell. Theoretical analysis has shown that, for example, a cell of Saccharomyces cerevisiae has enough energy to continuously sustain such gradient of strength about 1.5 kV/cm, the value sufficient for effective isoelectric focusing of cytoplasmic proteins. Focusing of enzymes could highly increase the effectiveness of an otherwise diffusion-limited metabolism of large cells by concentrating enzymes into small and distinct parts of a cytoplasm. By taking away an important physical constraint to the volume of cytoplasm, the intracellular isoelectric focusing enabled evolution of cells 3-4 order of magnitude larger than typical prokaryotic cells. This opened the way for the origin of phagocytosis and lately for the development of different forms of endosymbiosis, some of them resulting in an endosymbiotic origin of mitochondria and plastids. The large volume of a cell-enabled separation of nuclear and cytoplasmic compartments which was a precondition for separation of transcription and translation processes and therefore also for the origin of various RNA-preprocessing mechanisms. The possibility to regulate gene expression by postprocessing RNA and to regulate metabolism by an electrophoretic translocation enzymes between different parts of cytoplasm by changing their isoelectric points opened the way for cell and tissue differentiation and therefore for the origin of complex multicellular organisms.

De novo transcriptome analysis of Hevea brasiliensistissues by RNA-seq and screening for molecular markers

“…The characterization of mW and iP for the protein sequences translated from contigs with non-synonymous mutation showed that the mW from the mutated sequences was altered, but 250 sequences did not demonstrate any changes in iP values. Flegr [30] suggested that, since cell cytoplasm pH is stratified ranging from 6.4 to 7.2 in Eukaryotes, changes in the protein isoelectric point may directly influence the localization and reactions of proteins, and it is reasonable to assume that alterations to the global protein iP may interfere in interactions between proteins and complexes.…”

Elastic, not plastic species: Frozen plasticity theory and the origin of adaptive evolution in sexually reproducing organisms

“…It must be emphasized that the frozen plasticity theory has a much broader spectrum of evolutionary and ecological implications than has been suggested and discussed by students of particular hypotheses. In fact, the picture of evolutionary and ecological processes presented by the frozen plasticity theory differs in many respects from that provided by the current textbook theory of evolution; see Table 2 , [ 54 ] and (Flegr J.: Microevolutionary a macroevolutionary implication of Frozen plasticity theory of adaptive evolution, submitted). Most of these predictions could be tested empirically and should be analyzed in greater depth theoretically.…”

Evolution of the isoelectric point of mammalian proteins as a consequence of indels and adaptive evolution

“…This result may reflect recent work that has shown that pI shows a weak correlation with subcellular localization 39. However, our method is only considering shifts between compartments and does not take into account the possible cytoplasmic pI related stratification of the eukaryotic cell 8…”

“…For example, most membrane protein pI is acidic in Escherichia coli K12 that live in the basic intestines, and basic in Helicobacter pylori that are found in the acidic stomach 5, 7. Moreover, recent work hypothesizes that the eukaryotic cell cytoplasm is pI stratified, from pH 7.2 at the nuclear membrane, to 6.4 at the cell membrane 8. This cytoplasmic pH stratification hypothesis8 suggests that observed pI changes may have an important impact on signaling, localization of the proteins and as a consequence their reactions and function within the cells of different mammals.…”