This domain is the N-terminal periplasmic domain of the LapD and MoxY receptor proteins [1-2].

1: Identification of a two-component regulatory system controlling methanol dehydrogenase synthesis in Paracoccus denitrificans. Harms N, Reijnders WN, Anazawa H, van der Palen CJ, van Spanning RJ, Oltmann LF, Stouthamer AH; Mol Microbiol. 1993;8:457-470. PMID:8392137

2: Structural basis for c-di-GMP-mediated inside-out signaling controlling periplasmic proteolysis. Navarro MV, Newell PD, Krasteva PV, Chatterjee D, Madden DR, O'Toole GA, Sondermann H; PLoS Biol. 2011;9:e1000588. PMID:21304926