SidC is one of the effectors delivered by Legionella pneumophila into the host cell. Like its paralogue SdcA, SidC anchor on the Legionella-containing vacuole (LCV) through binding to phosphatidylinositol-4-phosphate (PI(4)P) to facilitate the recruitment of endoplasmic reticulum (ER) proteins. SidC is organised into four domains that are packed into an arch-like shape: the N- terminal SNL domain (Pfam:PF18219), the INS domain (which is inserted within the SNL domain), the PI(4)P binding domain or P4C domain (this entry), and a C-terminal domain (Pfam:PF20875). The lipid binding domain shows a four alpha-helix bundle with one end sealed by a C-terminal short beta hairpin and a highly positively charged pocket at the other end formed by two loops connecting the alpha-helices.s This pocket is thought to be the binding site, responsible for the stimulation of the E3 ligase activity of the SNL domain [1].

1: Structure of the Legionella Virulence Factor, SidC Reveals a Unique PI(4)P-Specific Binding Domain Essential for Its Targeting to the Bacterial Phagosome. Luo X, Wasilko DJ, Liu Y, Sun J, Wu X, Luo ZQ, Mao Y; PLoS Pathog. 2015;11:e1004965. PMID:26067986