This domain is found at the N-terminus of the Type II secretion secretion system protein E (GspE) and type IV pilus extensin ATPase PilB and near the C-terminus of the glycosyltransferase NfrB. A variant of this domain, called MshEN, binds cyclic di-GMP [4,6,7], which modulates the activity of the respective protein. The structure of this domain is now known [1,2,4].

1: The X-ray structure of the type II secretion system complex formed by the N-terminal domain of EpsE and the cytoplasmic domain of EpsL of Vibrio cholerae. Abendroth J, Murphy P, Sandkvist M, Bagdasarian M, Hol WG; J Mol Biol. 2005;348:845-855. PMID:15843017

2: Structure and function of the XpsE N-terminal domain, an essential component of the Xanthomonas campestris type II secretion system. Chen Y, Shiue SJ, Huang CW, Chang JL, Chien YL, Hu NT, Chan NL; J Biol Chem. 2005;280:42356-42363. PMID:16162504

3: Type II protein secretion and its relationship to bacterial type IV pili and archaeal flagella. Peabody CR, Chung YJ, Yen MR, Vidal-Ingigliardi D, Pugsley AP, Saier MH Jr; Microbiology. 2003;149:3051-3072. PMID:14600218

4: Nucleotide binding by the widespread high-affinity cyclic di-GMP receptor MshEN domain. Wang YC, Chin KH, Tu ZL, He J, Jones CJ, Sanchez DZ, Yildiz FH, Galperin MY, Chou SH; Nat Commun. 2016;7:12481. PMID:27578558

5: Structural cycle of the Thermus thermophilus PilF ATPase: the powering of type IVa pilus assembly. Collins R, Karuppiah V, Siebert CA, Dajani R, Thistlethwaite A, Derrick JP; Sci Rep. 2018;8:14022. PMID:30232337

6: A New Sugar for an Old Phage: a c-di-GMP-Dependent Polysaccharide Pathway Sensitizes Escherichia coli for Bacteriophage Infection. Sellner B, Prakapaite R, van Berkum M, Heinemann M, Harms A, Jenal U; mBio. 2021;12:e0324621. PMID:34903045

7: A Novel Locally c-di-GMP-Controlled Exopolysaccharide Synthase Required for Bacteriophage N4 Infection of Escherichia coli. Junkermeier EH, Hengge R; mBio. 2021;12:e0324921. PMID:34903052