Phospholipids containing ether-bound hydrocarbon-chains are essential for efficient phagocytosis and neutral lipids of the ester-type perturb development in Dictyostelium

The Amoebal Model for Macropinocytosis

Macropinocytosis is a relatively unexplored form of large-scale endocytosis driven by the actin cytoskeleton. Dictyostelium amoebae form macropinosomes from cups extended from the plasma membrane, then digest their contents and absorb the nutrients in the endo-lysosomal system. They use macropinocytosis for feeding, maintaining a high rate of fluid uptake that makes assay and experimentation easy. Mutants collected over the years identify cytoskeletal and signalling proteins required for macropinocytosis. Cups are organized around plasma membrane domains of intense PIP3, Ras and Rac signalling, proper formation of which also depends on the RasGAPs NF1 and RGBARG, PTEN, the PIP3-regulated protein kinases Akt and SGK and their activators PDK1 and TORC2, Rho proteins, plus other components yet to be identified. This PIP3 domain directs dendritic actin polymerization to the extending lip of macropinocytic cups by recruiting a ring of the SCAR/WAVE complex around itself and thus activating the Arp2/3 complex. The dynamics of PIP3 domains are proposed to shape macropinocytic cups from start to finish. The role of the Ras-PI3-kinase module in organizing feeding structures in unicellular organisms most likely predates its adoption into growth factor signalling, suggesting an evolutionary origin for growth factor signalling.

Sulfoquinovosylglyceryl ether, a new group of ether lipids from lake ball-forming green alga Aegagropilopsis moravica (family Pithophoraceae)

Ether lipids are a minor group of glycerolipids but widespread in nature, playing a vital function as membrane lipids, signalling molecules, or buoyant material. We have discovered sulfoquinovosylchimyl alcohol (1), a sulfonate-substituted glyceroglycolipid, from a lake ball-forming green alga Aegagropilopsis moravica (family Pithophoraceae), with the guidance of antimicrobial activity. The structure of 1, including absolute configurations of all sterogenic centers, was established by extensive NMR analysis, chemical degradation studies, and finally by total synthesis. Lipid 1 is an ether variant of a lyso-form of sulfoquinovosyldiacylglycerol, a chloroplast-specific membrane lipid, and thus represents a new lipid class, sulfoquinovosylglyceryl ether. A high occurrence of mobile life form in the family Pithophoraceae and a unique behaviour of chloroplasts reported in closely related Aegagropila linnaei, the famous lake-ball alga, implies a possible role of lipid 1 or its acyl derivatives in ecological adaptation to dysphotic niches.