This family of proteins with unknown function appears to be restricted to Enterobacteriaceae. This domain is found in a group of bacterial lipoproteins such as YajI from E.coli and SadB from Salmonella typhimurium. SadB is required for proper surface expression of the autotransporter adhesin SadA [1].

1: A trimeric lipoprotein assists in trimeric autotransporter biogenesis in enterobacteria. Grin I, Hartmann MD, Sauer G, Hernandez Alvarez B, Schutz M, Wagner S, Madlung J, Macek B, Felipe-Lopez A, Hensel M, Lupas A, Linke D; J Biol Chem. 2014;289:7388-7398. PMID:24369174