Post-translational modifications and the Warburg effect.

Post-translational modification (PTM) is an important step of signal transduction that transfers chemical groups such as phosphate, acetyl and glycosyl groups from one protein to another protein. As most of the PTMs are reversible, normal cells use PTMs as a 'switch' to determine the resting and proliferating state of cells that enables rapid and tight regulation of cell proliferation. In cancer cells, activation of oncogenes and/or inactivation of tumor suppressor genes provide continuous proliferative signals in part by adjusting the state of diverse PTMs of effector proteins that are involved in regulation of cell survival, cell cycle and proliferation, leading to abnormally fast proliferation of cancer cells. In addition to dysregulated proliferation, 'altered tumor metabolism' has recently been recognized as an emerging cancer hallmark. The most common metabolic phenotype of cancer is known as the Warburg effect or aerobic glycolysis that consists of increased glycolysis and enhanced lactate production even in the presence of oxygen. Although Otto Warburg observed aerobic glycolysis nearly 90 years ago, the detailed molecular mechanisms how increased glycolysis is regulated by oncogenic and/or tumor suppressive signaling pathways remain unclear. In this review, we summarize recent advances revealing how these signaling pathways reprogram metabolism through diverse PTMs to provide a metabolic advantage to cancer cells, thereby promoting tumor cell proliferation, tumorigenesis and tumor growth.

Impact of lithium-ion ordering on surface electronic states of Li(x)CoO2.

Li(x)CoO(2) exhibits intriguing electronic properties due to a strong electron correlation and complex interplay between Co and Li ions. However, fundamental understanding of the nanoscale distribution of Li ions and its effect on the electronic properties remains unclear. We use scanning tunneling microscopy and density functional theory to elucidate the degree of Li(x)CoO(2) surface electronic state modification that can be achieved by Li ordering. The surface Li ions are highly mobile and preferentially form a (1 × 1) hexagonal lattice, whereas the surface CoO(2) layer shows metallic and insulating phases, indicating the coexistence of ordered and disordered Li ions in the subsurface layer. These results provide evidence of novel electronic properties produced by spatially inhomogeneous Li-ordering patterns.

Dopant-pair structures segregated on a hydrogen-terminated Si(100) surface.

Novel atomic structures on a H-terminated Si(100)-(2x1)-H surface were found using scanning tunneling microscopy (STM). The structures are distinguishable only from Si dimers in empty-state STM images. They were observed on arsenic- and phosphorus-doped substrates, but not on boron-doped substrates. Surface density of these structures was found to be proportional to the dopant density in the substrate. First-principles calculations clarify that they are consisting of dopant pairs that are segregated from the bulk material. Hydrogen atoms attached to the dopant pair are found to flip between two positions on the surface due to a quantum effect.