Members of this family have so far been found in bacteria and mouse SwissProt or TrEMBL entries. However possible family members have also been identified in translated rat (Genbank:AW144450) and human (Genbank:AI478629) ESTs. A mouse family member has been named SIMPL (signalling molecule that associates with mouse pelle-like kinase). SIMPL appears to facilitate and/or regulate complex formation between IRAK/mPLK (IL-1 receptor-associated kinase) and IKK (inhibitor of kappa-B kinase) containing complexes, and thus regulate NF-kappa-B activity [1]. Separate experiments demonstrate that a mouse family member (named LaXp180) binds the Listeria monocytogenes surface protein ActA, which is a virulence factor that induces actin polymerisation. It may also bind stathmin, a protein involved in signal transduction and in the regulation of microtubule dynamics [2]. In bacteria its function is unknown, but it is thought to be located in the periplasm or outer membrane.

1: SIMPL is a tumor necrosis factor-specific regulator of nuclear factor-kappaB activity. Vig E, Green M, Liu Y, Yu KY, Kwon HJ, Tian J, Goebl MG, Harrington MA; J Biol Chem 2001;276:7859-7866. PMID:11096118

2: LaXp180, a mammalian ActA-binding protein, identified with the yeast two-hybrid system, co-localizes with intracellular Listeria monocytogenes. Pfeuffer T, Goebel W, Laubinger J, Bachmann M, Kuhn M; Cell Microbiol 2000;2:101-114. PMID:11207567