This domain is found at the N-terminus of the pre-pilin peptidases (Pfam:PF01478). Members of this entry have been characterised as bifunctional ([2]), and this domain may contain the N-methylation activity (EC:2.1.1.-). It consists of an intracellular region between a pair of transmembrane. This region contains an invariant proline and four almost fully conserved cysteines which bind Zn, as described for PilD from Pseudomonas aeruginosa [3]. The cysteines have been shown to be essential to the overall function of the enzyme [1,3].

1: Identification of active-site cysteines in the conserved domain of PilD, the bifunctional type IV pilin leader peptidase/N-methyltransferase of Pseudomonas aeruginosa. Strom MS, Bergman P, Lory S; J Biol Chem 1993;268:15788-15794. PMID:8340405

2: Posttranslational processing of type IV prepilin and homologs by PilD of Pseudomonas aeruginosa. Strom MS, Nunn DN, Lory S; Methods Enzymol 1994;235:527-540. PMID:8057924

3: Cell-free production of integral membrane aspartic acid proteases reveals zinc-dependent methyltransferase activity of the Pseudomonas aeruginosa prepilin peptidase PilD. Aly KA, Beebe ET, Chan CH, Goren MA, Sepulveda C, Makino S, Fox BG, Forest KT; Microbiologyopen. 2013;2:94-104. PMID:23255525