Archaeosomes are vesicles made of lipids from archaea. They possess many unique features in comparison to other lipid systems, with their high stability being the most prominent one, making them a promising system for biotechnological applications. Here, we report a preparation protocol of large unilamellar vesicles, giant unilamellar vesicles (GUVs), and nanodiscs from archaeal lipids with incorporated cholesterol. Incorporation of cholesterol led to additional increase in thermal stability of vesicles. Surface plasmon resonance, sedimentation assays, intrinsic tryptophan fluorescence measurements, calcein release experiments, and GUVs experiments showed that members of cholesterol-dependent cytolysins, listeriolysin O (LLO), and perfringolysin O (PFO), bind to cholesterol-rich archaeosomes and thereby retain their pore-forming activity. Interestingly, we observed specific binding of LLO, but not PFO, to archaeosomes even in the absence of cholesterol. This suggests a new capacity of LLO to bind to carbohydrate headgroups of archaeal lipids. Furthermore, we were able to express LLO inside GUVs by cell-free expression. GUVs made from archaeal lipids were highly stable, which could be beneficial for synthetic biology applications. In summary, our results describe novel model membrane systems for studying membrane interactions of proteins and their potential use in biotechnology.
Pore-forming toxins are an important component of the venom of many animals. Actinoporins are potent cytolysins that were first detected in the venom of sea anemones; however, they are occasionally found in animals other than cnidarians and are expanded in a few predatory gastropods. Here, we report the presence of 27 unique actinoporin-like genes with monophyletic origin in Mytilus galloprovincialis, which we have termed mytiporins. These mytiporins exhibited a remarkable level of molecular diversity and gene presence-absence variation, which warranted further studies aimed at elucidating their functional role. We structurally and functionally characterized mytiporin-1 and found significant differences from the archetypal actinoporin fragaceatoxin C. Mytiporin-1 showed weaker permeabilization activity, no specificity towards sphingomyelin, and weak activity in model lipid systems with negatively charged lipids. In contrast to fragaceatoxin C, which forms octameric pores, functional mytiporin-1 pores on negatively charged lipid membranes were hexameric. Similar hexameric pores were observed for coluporin-26 from Cumia reticulata and a conoporin from Conus andremenezi. This indicates that also other molluscan actinoporin-like proteins differ from fragaceatoxin C. Although the functional role of mytiporins in the context of molluscan physiology remains to be elucidated, the lineage-specific gene family expansion event that characterizes mytiporins indicates that strong selective forces acted on their molecular diversification. Given the tissue distribution of mytiporins, this process may have broadened the taxonomic breadth of their biological targets, which would have important implications for digestive processes or mucosal immunity.
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