A Unique Phosphatidylinositol Bearing a Novel Branched-Chain Fatty Acid from Rhodococcus equi Binds to Influenza Virus Hemagglutinin and Inhibits the Infection of Cells

Abstract

From the aquatic bacterium Rhodococcus equi strain S₄₂₀, we isolated a substance that strongly binds to influenza viruses. Structural analyses revealed that it is a unique type of phosphatidylinositol (Ptdlns) bearing a branched-chain fatty acid (14-methyloctadecanoic acid). In a TLC/virus-binding immunostaining assay, this Ptdlns bound to all subtypes of hemagglutinin (HA) of influenza A viruses tested, isolated from humans, ducks and swine, and also to human influenza B viruses. Furthermore, the Ptdlns significantly prevented the infection of MDCK cells by influenza viruses, and also inhibited the virusmediated hemagglutination and low pH-induced hemolysis of human erythrocytes, which represents the fusogenic activities of the viral HA. We also used purified hemagglutinin instead of virions to examine the interaction between viral HA and Ptdlns, showing that the Ptdlns binds to hemagglutinin. These findings indicate that the inhibitory mechanism of Ptdlns on the influenza virus infection may be through its binding to viral HA spikes and host cell endosomal/lysosomal membranes, which are mediated by the function of viral HA.