This domain is found at the C-terminal end of HTH-type transcriptional regulator Rgg from Streptococcus gordonii, and similar proteins predominantly found in Firmicutes. Rgg is a peptide pheromone receptor that directly binds pheromones transported to the cytosol. The large C-terminal repeat domain contains five HTH folds and a capping helix that form a right-handed superhelical structure, resembling a TPR domain superhelix [1-5]. This domain is found associated with the N-terminal Pfam:PF01381.

1: Structure of peptide sex pheromone receptor PrgX and PrgX/pheromone complexes and regulation of conjugation in Enterococcus faecalis. Shi K, Brown CK, Gu ZY, Kozlowicz BK, Dunny GM, Ohlendorf DH, Earhart CA; Proc Natl Acad Sci U S A. 2005;102:18596-18601. PMID:16339309

2: Molecular basis for control of conjugation by bacterial pheromone and inhibitor peptides. Kozlowicz BK, Shi K, Gu ZY, Ohlendorf DH, Earhart CA, Dunny GM; Mol Microbiol. 2006;62:958-969. PMID:17038121

3: Rgg protein structure-function and inhibition by cyclic peptide compounds. Parashar V, Aggarwal C, Federle MJ, Neiditch MB; Proc Natl Acad Sci U S A. 2015;112:5177-5182. PMID:25847993

4: Structural and functional analysis of RopB: a major virulence regulator in Streptococcus pyogenes. Makthal N, Gavagan M, Do H, Olsen RJ, Musser JM, Kumaraswami M; Mol Microbiol. 2016;99:1119-1133. PMID:26714274

5: Activating mutations in quorum-sensing regulator Rgg2 and its conformational flexibility in the absence of an intermolecular disulfide bond. Wilkening RV, Capodagli GC, Khataokar A, Tylor KM, Neiditch MB, Federle MJ; J Biol Chem. 2017;292:20544-20557. PMID:29030429