The C-terminus of H-Ras as a target for the covalent binding of reactive compounds modulating Ras-dependent pathways.

Ras proteins are crucial players in differentiation and oncogenesis and constitute important drug targets. The localization and activity of Ras proteins are highly dependent on posttranslational modifications at their C-termini. In addition to an isoprenylated cysteine, H-Ras, but not other Ras proteins, possesses two cysteine residues (C181 and C184) in the C-terminal hypervariable domain that act as palmitoylation sites in cells. Cyclopentenone prostaglandins (cyPG) are reactive lipidic mediators that covalently bind to H-Ras and activate H-Ras dependent pathways. Dienone cyPG, such as 15-deoxy-Δ(12,14)-PGJ(2) (15d-PGJ(2)) and Δ(12)-PGJ(2) selectively bind to the H-Ras hypervariable domain. Here we show that these cyPG bind simultaneously C181 and C184 of H-Ras, thus potentially altering the conformational tendencies of the hypervariable domain. Based on these results, we have explored the capacity of several bifunctional cysteine reactive small molecules to bind to the hypervariable domain of H-Ras proteins. Interestingly, phenylarsine oxide (PAO), a widely used tyrosine phosphatase inhibitor, and dibromobimane, a cross-linking agent used for cysteine mapping, effectively bind H-Ras hypervariable domain. The interaction of PAO with H-Ras takes place in vitro and in cells and blocks modification of H-Ras by 15d-PGJ(2). Moreover, PAO treatment selectively alters H-Ras membrane partition and the pattern of H-Ras activation in cells, from the plasma membrane to endomembranes. These results identify H-Ras as a novel target for PAO. More importantly, these observations reveal that small molecules or reactive intermediates interacting with spatially vicinal cysteines induce intramolecular cross-linking of H-Ras C-terminus potentially contributing to the modulation of Ras-dependent pathways.

Science, technique, technology: passages between matter and knowledge in imperial Chinese agriculture.

Many historians today prefer to speak of knowledge and practice rather than science and technology. Here I argue for the value of reinstating the terms science, techniques and technology as tools for a more precise analysis of governmentality and the workings of power. My tactic is to use these three categories and their articulations to highlight flows between matter and ideas in the production and reproduction of knowledge. In any society, agriculture offers a wonderfully rich case of how ideas, material goods and social relations interweave. In China agronomy was a science of state, the basis of legitimate rule. I compare different genres of agronomic treatise to highlight what officials, landowners and peasants respectively contributed to, and expected from, this charged natural knowledge. I ask how new forms of textual and graphic inscription for encoding agronomic knowledge facilitated its dissemination and ask how successful this knowledge proved when rematerialized and tested as concrete artefacts or techniques. I highlight forms of innovation in response to crisis, and outline the overlapping interpretative frameworks within which the material applications of Chinese agricultural science confirmed and extended its truth across space and time.