NfeD-like proteins are widely distributed throughout prokaryotes and are frequently associated with genes encoding stomatin-like proteins (slipins). There appear to be three major groups: an ancestral group with only an N-terminal serine protease domain and this C-terminal beta sheet-rich domain which is structurally very similar to the OB-fold domain, associated with its neighbouring slipin cluster; a second major group with an additional middle, membrane-spanning domain, associated in some species with eoslipin and in others with yqfA; a final 'artificial' group which unites truncated forms lacking the protease region and associated with their ancestral gene partner, either yqfA or eoslipin. This NefD, C-terminal, domain appears to be the major one for relating to the associated protein. NfeD homologues are clearly reliant on their conserved gene neighbour which is assumed to be necessary for function, either through direct physical interaction or by functioning in the same pathway, possibly involve with lipid-rafts [1].

1: The NfeD Protein Family and Its Conserved Gene Neighbours Throughout Prokaryotes: Functional Implications for Stomatin-Like Proteins. Green JB, Lower RP, Young JP; J Mol Evol. 2009;69:657-667. PMID:20012272