Soft x-ray laser experiments at Novette Laser Facility

We discuss the results of and future plans for experiments to study the possibility of producing an x-ray laser. The schemes we have investigated are all pumped by the Novette Laser, operated at short pulse (tau/sub L/ approx. 100 psec) and an incident wavelength of lambda /sub L/ approx. 0.53 ..mu..m. We have studied the possibility of lasing at 53.6, 68.0 to 72.0, 119.0, and 153.0 eV, using the inversion methods of resonant photo-excitation, collisional excitation, and three-body recombination

Defensins from insects and plants interact with fungal glucosylceramides

Growth of the yeast species Candida albicans and Pichia pastoris is inhibited by RsAFP2, a plant defensin isolated from radish seed (Raphanus sativus), at micromolar concentrations. In contrast, gcs-deletion mutants of both yeast species are resistant toward RsAFP2. GCS genes encode UDP-glucose:ceramide glucosyltransferases, which catalyze the final step in the biosynthesis of the membrane lipid glucosylceramide. In an enzyme-linked immunosorbent assay-based binding assay, RsAFP2 was found to interact with glucosylceramides isolated from P. pastoris but not with soybean nor human glucosylceramides. Furthermore, the P. pastoris parental strain is sensitive toward RsAFP2-induced membrane permeabilization, whereas the corresponding gcs-deletion mutant is highly resistant to RsAFP2-mediated membrane permeabilization. A model for the mode of action of RsAFP2 is presented in which all of these findings are linked. Similarly to RsAFP2, heliomicin, a defensin-like peptide from the insect Heliothis virescens, is active on C. albicans and P. pastoris parental strains but displays no activity on the gcs-deletion mutants of both yeast species. Furthermore, heliomicin interacts with glucosylceramides isolated from P. pastoris and soybean but not with human glucosylceramides. These data indicate that structurally homologous anti-fungal peptides present in species from different eukaryotic kingdoms interact with the same target in the fungal plasma membrane, namely glucosylceramides, and as such support the hypothesis that defensins from plants and insects have evolved from a single precursor

Crystal structure of the guanylyl cyclase Cya2

Cyclic GMP (cGMP) is an important second messenger in eukaryotes. It is formed by guanylyl cyclases (GCs), members of the nucleotidyl cyclases class III, which also comprises adenylyl cyclases (ACs) from most organisms. To date, no structures of eukaryotic GCs are available, and all bacterial class III proteins were found to be ACs. Here we describe the biochemical and structural characterization of the class III cyclase Cya2 from cyanobacterium Synechocystis PCC6803. Cya2 shows high specificity for GTP versus ATP, revealing it to be the first bacterial GC, and sequence similarity searches indicate that GCs are also present in other bacteria. The crystal structure of Cya2 provides first structural insights into the universal GC family. Structure and mutagenesis studies show that a conserved glutamate, assisted by an interacting lysine, dominates substrate selection by forming hydrogen bonds to the substrate base. We find, however, that a second residue involved in substrate selection has an unexpected sterical role in GCs, different from its hydrogen bonding function in the related ACs. The structure identifies a tyrosine that lines the guanine binding pocket as additional residue contributing to substrate specificity. Furthermore, we find that substrate specificity stems from faster turnover of GTP, rather than different affinities for GTP and ATP, implying that the specificity-determining interactions are established after the binding step

Soft Xray Laser Experiments at the Novette Laser Facility

We will summarize previous, as well as ongoing, work whose sole purpose is to demonstrate laser-pumped soft xray laser. We have concentrated our efforts on three possible laser schemes: 1) resonant photoexcitation, 2) collisional excitation, and 3) collisional recombination. Our earliest attempt only demonstrated a small gain of approximately 0.5-1 cm on the recombination scheme. Nevertheless, we have begun a multifaceted experimental program to determine what the crucial physics for all three schemes are, and where our experiments or predictions could have fallen short. We have combined our efforts with other facilities, such as KMS Fusion, Inc., where, with their Chroma Laser Facility, they are performing experiments to 1) test for line coincidences to 3 mA accuracy, 2) validating predicted density and temperature profiles using laser iterferometry and xray spectroscopy, and 3) testing the kinetics of inversion using a specialized experimental setup which is easily diagnosed, yet whose geometry closely resembles an xray laser target.</jats:p