Lasso peptides are natural products with a unique three dimensional structure resembling a lariat knot. They are from ribosomal origin and are post-translationally modified by two enzymes (B and C), one of which shares little similarity to enzymes outside of lasso peptide biosynthetic gene clusters and as such is a useful target for genome mining. In this study, we demonstrate a B protein-centric genome mining approach through which we were able to identify 102 putative lasso peptide biosynthetic gene clusters from a total of 87 different proteobacterial strains. Ten of these clusters were cloned into the pET41a expression vector, optimized through incorporation of a ribosomal binding site and heterologously expressed in Escherichia coli BL21(DE3). All 12 predicted lasso peptides (namely burhizin, caulonodin I, caulonodin II, caulonodin III, rhodanodin, rubrivinodin, sphingonodin I, sphingonodin II, syanodin I, sphingopyxin I, sphingopyxin II, and zucinodin) were detected by high-resolution Fourier transform mass spectrometry and their proposed primary structure was confirmed through tandem mass spectrometry. High yields (ranging from 0.4 to 5.2 mg/L) were observable for eight of these compounds, while thermostability assays revealed five new representatives of heat labile lasso peptides.

Parasites causing malaria need to migrate in order to penetrate tissue barriers and enter host cells. Here we show that the actin filament-binding protein coronin regulates gliding motility in Plasmodium berghei sporozoites, the highly motile forms of a rodent malaria-causing parasite transmitted by mosquitoes. Parasites lacking coronin show motility defects that impair colonization of the mosquito salivary glands but not migration in the skin, yet result in decreased transmission efficiency. In non-motile sporozoites low calcium concentrations mediate actin-independent coronin localization to the periphery. Engagement of extracellular ligands triggers an intracellular calcium release followed by the actin-dependent relocalization of coronin to the rear and initiation of motility. Mutational analysis and imaging suggest that coronin organizes actin filaments for productive motility. Using coronin-mCherry as a marker for the presence of actin filaments we found that protein kinase A contributes to actin filament disassembly. We finally speculate that calcium and cAMP-mediated signaling regulate a switch from rapid parasite motility to host cell invasion by differentially influencing actin dynamics.

Malaria is transmitted when an infected Anopheles mosquito deposits Plasmodium sporozoites in the skin during a bite. Sporozoites are formed within oocysts at the mosquito midgut wall and are released into the hemolymph, from where they invade the salivary glands and are subsequently transmitted to the vertebrate host. We found that a thrombospondin-repeat containing sporozoite-specific protein named thrombospondin-releated protein 1 (TRP1) is important for oocyst egress and salivary gland invasion, and hence for the transmission of malaria. We imaged the release of sporozoites from oocysts in situ, which was preceded by active motility. Parasites lacking TRP1 failed to migrate within oocysts and did not egress, suggesting that TRP1 is a vital component of the events that precede intra-oocyst motility and subsequently sporozoite egress and salivary gland invasion.DOI: http://dx.doi.org/10.7554/eLife.19157.001

Inserted (I) domains function as ligand-binding domains in adhesins that support cell adhesion and migration in many eukaryotic phyla. These adhesins include integrin αβ heterodimers in metazoans and single subunit transmembrane proteins in apicomplexans such as TRAP in Plasmodium and MIC2 in Toxoplasma. Here we show that the I domain of TRAP is essential for sporozoite gliding motility, mosquito salivary gland invasion and mouse infection. Its replacement with the I domain from Toxoplasma MIC2 fully restores tissue invasion and parasite transmission, while replacement with the aX I domain from human integrins still partially restores liver infection. Mutations around the ligand binding site allowed salivary gland invasion but led to inefficient transmission to the rodent host. These results suggest that apicomplexan parasites appropriated polyspecific I domains in part for their ability to engage with multiple ligands and to provide traction for emigration into diverse organs in distant phyla.