Pyrrolizidine alkaloids (PAs) are a group of natural products with important biological activities. The discovery and characterization of the multifunctional FAD-dependent enzyme LgnC is now described. The enzyme is shown to convert indolizidine intermediates into pyrrolizidines through an unusual ring expansion/contraction mechanism, and catalyze the biosynthesis of new bacterial PAs, the so-called legonmycins. By genome-driven analysis, heterologous expression, and gene inactivation, the legonmycins were also shown to originate from non-ribosomal peptide synthetases (NRPSs). The biosynthetic origin of bacterial PAs has thus been disclosed for the first time.

Genome sequencing identified a fluorinase gene in the marine bacterium Streptomyces xinghaiensis NRRL B-24674. Fermentation of the organism with inorganic fluoride (2 mM) demonstrated that the organism could biosynthesise fluoroacetate and that fluoroacetate production is sea-salt dependent. This is the first fluorometabolite producing microorganism identified from the marine environment.

(2R3S4S)-5-Fluoro-2,3,4-trihydroxypentanoic acid (5-FHPA) has been discovered as a new fluorometabolite in the soil bacterium Streptomyces sp. MA37.

Glycoproteins secreted by cells play essential roles in the regulation of extracellular activities. Secreted glycoproteins are often reflective of cellular status, and thus glycoproteins from easily accessible bodily fluids can serve as excellent biomarkers for disease detection. Cultured cells have been extensively employed as models in the research fields of biology and biomedicine, and global analysis of glycoproteins secreted from these cells provides insights into cellular activities and glycoprotein functions. However, comprehensive identification and quantification of secreted glycoproteins is a daunting task because of their low abundances compared with the high-abundance serum proteins required for cell growth and proliferation. Several studies employed serum-free media to analyze secreted proteins, but it has been shown that serum starvation, even for a short period of time, can alter protein secretion. To overcome these issues, we developed a method to globally characterize secreted glycoproteins and their N-glycosylation sites from cultured cells by combining selective enrichment of secreted glycoproteins with a boosting approach. The results demonstrated the importance of the boosting sample selection and the boostingto-sample ratio for improving the coverage of secreted glycoproteins. The method was applied to globally quantify secreted glycoproteins from THP-1 monocytes and macrophages in response to lipopolysaccharides (LPS) and from Hep G2 cells treated with TGF-β without serum starvation. We found differentially secreted glycoproteins in these model systems that showed the cellular response to the immune activation or the epithelial-to-mesenchymal transition. Benefiting from the selective enrichment and the signal enhancement of low-abundance secreted glycoproteins, this method can be extensively applied to study secreted glycoproteins without serum starvation, which will provide a better understanding of protein secretion and cellular activity.

The food-borne bacterial pathogen Salmonella Typhimurium uses a type III protein secretion system to deliver multiple proteins into host cells. These secreted effectors modulate host cell functions and activate specific signalling cascades that result in the production of pro-inflammatory cytokines and intestinal inflammation. Some of the Salmonella -encoded effectors counter this inflammatory response and help to preserve host homeostasis. We demonstrate that the Salmonella effector protein SopD, which is required for pathogenesis, functions to both activate and inhibit the inflammatory response by targeting the Rab8 GTPase, a negative regulator of inflammation. We show that SopD has GTPase activating protein activity for Rab8, and therefore inhibits this GTPase and stimulates inflammation. We also show that SopD activates Rab8 by displacing it from its cognate guanosine dissociation inhibitor resulting in the stimulation of a signaling cascade that suppresses inflammation. We solved the crystal structure of SopD in association with Rab8 to 2.3 Å resolution, which reveals a unique contact interface underlying these complex interactions. These findings show the remarkable evolution of a bacterial effector protein to exert both agonistic and antagonistic activities toward the same host cellular target to modulate the inflammatory response.