RcpB is part of the Tad operon of proteins [1]. The Tad (tight adherence) macromolecular transport system, present in many bacterial and archaeal species, represents an ancient and major new subtype of type II secretion. The three Rcp proteins (RcpA, RcpB, and RcpC) and TadD, a putative lipoprotein, are localised to the bacterial outer membrane [2].

1: The tad locus: postcards from the widespread colonization island. Tomich M, Planet PJ, Figurski DH; Nat Rev Microbiol. 2007;5:363-375. PMID:17435791

2: Outer membrane components of the Tad (tight adherence) secreton of Aggregatibacter actinomycetemcomitans. Clock SA, Planet PJ, Perez BA, Figurski DH; J Bacteriol. 2008;190:980-990. PMID:18055598