Phosphatidylinositol transfer protein alpha (PITPalpha) selectively transports and promotes exchange of phosphatidylinositol (PI) and phosphatidylcholine (PC) between lipid bilayers. In higher eukaryotes PITPalpha is required for cellular functions such as phospholipase C-mediated signaling, regulated exocytosis, and secretory vesicle formation. We have determined the crystal structure of human PITPalpha bound to its physiological ligand, PI, at 2.95 A resolution. The structure identifies the critical side chains within the lipid-headgroup binding pocket that define the exquisite specificity for PI. Mutational analysis of the PI binding pocket is in good agreement with the structural data and allows manipulation of functional properties of PITPalpha. Surprisingly, there are no major conformational differences between PI- and PC-loaded PITPalpha, despite previous predictions. In the crystal, PITPalpha-PI is dimeric, with two identical dimers in the asymmetric unit. The dimer interface masks precisely the sequence we identify as contributing to PITPalpha membrane interaction. Our structure represents a soluble, transport-competent form of PI-loaded PITPalpha.

The crystal structure of the catalytic domain from the MAPK phosphatase Pyst1 (Pyst1–CD) has been determined at 2.35 Å. The structure adopts a protein tyrosine phosphatase (PTPase) fold with a shallow active site that displays a distorted geometry in the absence of its substrate with some similarity to the dual–specificity phosphatase cdc25. Functional characterization of Pyst1–CD indicates it is sufficient to dephosphorylate activated ERK2 in vitro. Kinetic analysis of Pyst1 and Pyst1–CD using the substrate p–nitrophenyl phosphate (pNPP) reveals that both molecules undergo catalytic activation in the presence of recombinant inactive ERK2, switching from a low– to high–activity form. Mutation of Asp 262, located 5.5 Å distal to the active site, demonstrates it is essential for catalysis in the high–activity ERK2–dependent conformation of Pyst1 but not for the low–activity ERK2–independent form, suggesting that ERK2 induces closure of the Asp 262 loop over the active site, thereby enhancing Pyst1 catalytic efficiency.

Molten salt oxidation is reviewed as a potential near term alternative technology for the destruction of chemical agents. Initial tests completed by the US Army in 1975 showed the promise of achieving very high removal efficiencies on actual agents. Recent testing by DOE has verified the potential for very low PIC and dioxin or furan releases. To further explore the possible application of this technology to chemical agent destruction, a molten salt reactor and associated equipment was designed to process a nominal 50 kg/h of Sarin. Mass and energy balances are presented for process conditions representing a range of molten salt potential operational modes and schemes for enhancing plant capacity. Process economics are presented.

Received 23 October 1963DOI:https://doi.org/10.1103/PhysRevLett.11.527©1963 American Physical Society