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Lytic polysaccharide monooxygenases (LPMOs) are industrial enzymes which are gaining use in second generation bioethanol production from lignocellulose by acting in synergy with glycoside hydrolases. Here we present the X-ray crystal structure of an AA9 fungal LPMO from Aspergillus fumigatus and a variant which has been shown to have better performance at elevated temperatures. Based on the structures, thermal denaturation data and theoretical calculations, we provide a suggestion for the structural basis of the improved stability.

An endophytic streptomycete (NRRL 30566) is described and partially characterized from a fern-leaved grevillea (Grevillea pteridifolia) tree growing in the Northern Territory of Australia. This endophytic streptomycete produces, in culture, novel antibiotics - the kakadumycins. Methods are outlined for the production and chemical characterization of kakadumycin A and related compounds. This antibiotic is structurally related to a quinoxaline antibiotic, echinomycin. Each contains, by virtue of their amino acid compositions, alanine, serine and an unknown amino acid. Other biological, spectral and chromatographic differences between these two compounds occur and are given. Kakadumycin A has wide spectrum antibiotic activity, especially against Gram-positive bacteria, and it generally displays better bioactivity than echinomycin. For instance, against Bacillus anthracis strains, kakadumycin A has minimum inhibitory concentrations of 0.2-0.3 microg x ml(-1) in contrast to echinomycin at 1.0-1.2 microg x ml(-1). Both echinomycin and kakadumycin A have impressive activity against the malarial parasite Plasmodium falciparum with LD(50)s in the range of 7-10 ng x ml(-1). In macromolecular synthesis assays both kakadumycin A and echinomycin have similar effects on the inhibition of RNA synthesis. It appears that the endophytic Streptomyces sp. offer some promise for the discovery of novel antibiotics with pharmacological potential.

The general thermodynamic principles behind pH driven conformational transitions of biological macromolecules are well understood. What is less obvious is how they can be used to engineer pH switches in proteins. The acid unfolding of staphylococcal nuclease (SNase) was used to illustrate different factors that can affect pH-driven conformational transitions. Acid unfolding is a structural transition driven by preferential H(+) binding to the acid unfolded state (U) over the native (N) state of a protein. It is the result of carboxylic groups that titrate with more normal pK(a) values in the U state than in the N state. Acid unfolding profiles of proteins reflect a balance between electrostatic and non-electrostatic contributions to stability. Several strategies were used in attempts to turn SNase into an acid insensitive protein: (1) enhancing global stability of the protein with mutagenesis or with osmolytes, (2) use of high salt concentrations to screen Coulomb interactions, (3) stabilizing the N state through specific anion effects, (4) removing Asp or Glu residues that titrate with depressed pK(a) values in the N state, and (5) removing basic residues that might have strong repulsive interactions in the N state at low pH. The only effective way to engineer acid resistance in SNase is not through modulation of pK(a) values of Asp/Glu but by enhancing the global stability of the protein. Modulation of pH-driven conformational transitions by selective manipulation of the electrostatic component of the switch is an extremely difficult undertaking.

Graft-versus-host disease (GVHD) is a serious complication of allogeneic bone marrow transplantation, and donor T cells are indispensable for GVHD. Current therapies have limited efficacy, selectivity, and high toxicities. We used a novel flow cytometry technique for the analysis of intracellular phosphorylation events in single cells in murine BMT models to identify and validate novel GVHD drug targets.1-7 This method circumvents the requirement for large numbers of purified cells, unlike western blots. We defined a signaling profile for alloactivated T cells in vivo and identified the phosphorylation of ERK1/2 and STAT-3 as important events during T-cell (allo)activation in GVHD. We establish that interference with STAT-3 phosphorylation can inhibit T-cell activation and proliferation in vitro and GVHD in vivo. This suggests that phospho-specific flow cytometry is useful for the identification of promising drug targets, and ERK1/2 and STAT-3 phosphorylation in alloactivated T cells may be important for GVHD.

Although thymic graft-versus-host-disease (tGVHD) has been recognized as an important contributor to impaired T cell reconstitution, limited T cell repertoire and increased infection risk in patients with GVHD, the molecular basis of interactions between donor alloreactive T cells, donor bone marrow (BM)-derived thymocytes, and host hematopoietic and non-hematopoietic thymic stromal cells in GVHD has not been well-defined. Here we analyzed the role of molecules relevant for T cell trafficking, cytolytic function, and co-stimulation and co-inhibition of alloreactive T cells in tGVHD. We first demonstrated that thymic output (as measured by RAG2+ splenic recent thymic emigrants) as well as the thymic cellularity (especially of CD4+CD8+ thymocytes) were inversely proportional to numbers of mature donor T cells infused with the allograft, suggesting that tGVHD severity was inversely associated with thymic function. We then studied the migration of alloreactive donor T cells in vivo with bioluminescence imaging (BLI) and found that luciferase-expressing donor T cells infiltrated the thymus within one week after allogeneic bone marrow transplantation (BMT) (Fig. 1). Upon adoptive transfer of CFSE-labeled donor T cells we noted that thymus-infiltrating alloreactive donor T cells were largely fast-proliferating (CFSElo) and highly activated (CD25+ CD44+). We analyzed the importance of T cell trafficking molecules for tGVHD using mice deficient for certain trafficking molecules, and assessed tGVHD by loss of BM-derived CD4+CD8+ thymocytes. We found that CCR9, b7 integrin subunit, and PSGL-1 were all partially required for tGVHD, while L-selectin and aE integrin subunit may be dispensable (Fig. 2A). Similarly, we examined the role of T cell cytolytic pathways for tGVHD, and found that FasL and TRAIL were required for tGVHD, but that perforin and TNF were dispensable (Fig. 2B). Finally, we assessed the role of various T cell co-stimulatory and co-inhibitory molecules for tGVHD, and found that CEACAM1, OX40 and CTLA4 were required, while GITR was partially required and ICOS was dispensable (Fig. 2C). Upon further analysis of donor BM-derived thymocytes, we observed that Bcl-2 expression in donor BM-derived thymocytes was decreased in recipients with GVHD vs. those without GVHD, which suggests that survival of thymocytes is decreased during tGVHD. Hollander and others have previously demonstrated in non-irradiated GVH reaction models that host non-hematopoietic thymic stroma may be an important target for donor alloreactive T cells. We assessed the expression of the death receptors Fas and DR5 in thymic stroma from normal and irradiated (850 cGy) BALB/c mice. We observed that in particular, MHC class II-negative stroma (endothelial cells and fibroblasts), as well as a population of MHC class II-intermediate stroma (epithelial cells) upregulated the expression of both Fas and DR5 after irradiation. Our study defines the specific pathways for cytolysis, trafficking and immune modulation involved in tGVHD and suggests selective therapeutic targets to attenuate tGVHD and improve post-transplant T-cell reconstitution in patients with GVHD. Fig 1. BLI demonstrate a distinct distribution pattern for alloreactive donor T cells in allogeneic BMT recipients, Allogeneic Balb/c recipients show a strong signal on day 4 post-transparent after transfer of 10×108 luc+ splenocytes as measured by total body photon emission. Ex vivo imaging confirms the infiltration of luc+ splenocytes to the thymus. Fig 1. BLI demonstrate a distinct distribution pattern for alloreactive donor T cells in allogeneic BMT recipients, Allogeneic Balb/c recipients show a strong signal on day 4 post-transparent after transfer of 10×108 luc+ splenocytes as measured by total body photon emission. Ex vivo imaging confirms the infiltration of luc+ splenocytes to the thymus. Fig 2. We assessed the role of molecules relevant for T cell trafficking (A), cytolytic function (B), and co-stimulation, co-inhibition (C). Irradiated BALB/c mice received 5×106 T cell depleted C57BL/6 bone marrow + 0.25×106 purified splenic T cells. Absolute numbers of donor-BM-derived CD4+CD8+ thymocytes are shown. Black bars indicate means. p-values were calculated vs. recipients of WT T cells(*p

Graft-versus-host-disease (GVHD) is a serious complication of allogeneic bone marrow transplantation (allo-BMT). The physiology of GVHD is dominated by alloactivated donor T cells, yet current treatments are often nonspecific and offer limited efficacy with relatively high toxicities. We screened for novel drug targets in alloactivated T cells in a murine allo-BMT model using a flow cytometric technique for the in vivo analysis of intracellular signaling. We defined the signaling profile of normal T cells and alloreactive T cells during GVHD, focusing on pathways involved in T cell receptor (TCR), costimulatory, and cytokine signaling. This analysis revealed that although proteins in multiple pathways (MAP kinases, PI3K, Jak/STAT signaling) were all heavily phosphorylated in alloactivated T cells, phosphorylation of STAT-3 and ERK1/2 were particularly prominently increased in donor alloactivated CD4 T cells. We further analyzed the importance of STAT-3 and ERK1/2 signaling in alloactivated T cells via the use of small-molecule inhibitors of STAT-3 (curcurbitacin E/I) and ERK1/2 phosphorylation (SL327). Treatment with these inhibitors attenuated T cell proliferation in response to anti-CD3+CD28 stimulation and in mixed leukocyte reactions in vitro in a dose-dependent fashion (figure 1). Figure 1 Figure 1. Pre-incubation of donor splenocytes with cucurbitacin E significanly reduced T cell activation (CD25, CD69) at 24 hours in adoptive transfer experiments in vivo (p Figure 2 Figure 2. We conclude that flow cytometric analysis of signaling pathways in single cells represents a novel methodology to assess the in vivo signaling profiles of specific cell populations in order to select drug targets for further study. STAT-3 and ERK1/2 phosphorylation may also represent potential targets to selectively inhibit donor T cell alloactivation and proliferation in GVHD.