This is a subdomain of a Rab GTPase-activating protein (GAP) effector from Legionella pneumophilia. This GAP modulates Rab enzymes that act as molecular switches in regulating vesicular transport in eukaryotic cells. This N-terminal subdomain belongs to the the GAP domain of the protein. The catalytic arginine finger (Arg444) is located within this sub-domain and it is the only arginine residue required for GAP activity [1].

1: Structural analyses of Legionella LepB reveal a new GAP fold that catalytically mimics eukaryotic RasGAP. Yu Q, Hu L, Yao Q, Zhu Y, Dong N, Wang DC, Shao F; Cell Res. 2013;23:775-787. PMID:23588383