Nodulation formation efficiency D (NfeD) is a membrane-bound ClpP-class protease.
Nodulation formation efficiency D (NfeD; stomatin operon partner protein, STOPP; DUF107) is a member of membrane-anchored ClpP-class proteases. Currently, more than 300 NfeD homologs have been identified - all of which are bacterial or archaeal in origin. Majority of these genomes have been shown to possess operons containing a homologous NfeD/stomatin gene pair, causing NfeD to be previously named STOPP (stomatin operon partner protein). NfeD homologs can be divided into two groups: long and short forms. Long-form homologs have a putative ClpP-class serine protease domain while the short form homologs do not. Downstream from the ClpP-class domain is the so-called NfeD or DUF107 domain. N-terminal region of the NfeD homolog PH1510 (1510-N or PH1510-N) from Pyrococcus horikoshii has been shown to possess serine protease activity and has a Ser-Lys catalytic dyad, preferentially cleaving hydrophobic substrates. Difference in oligomeric form and catalytic residues between 1510-N (forming a dimer) and ClpP (forming a tetradecamer) shows a possible functional difference: 1510-N is likely to have a regulatory function while ClpP is involved in protein quality control.