This family of proteins is found in the IncC family of broad-host-range plasmids which enables the spread of antibiotic resistance genes among human enteric pathogens. Recently, AcaB member has been characterised as a transcriptional regulator that plays a crucial role in the regulation of IncC conjugation. It is a DNA binding protein which binds upstream of the acaDB promoter to increase its transcription and, in turn, acaDB activates the transcription of IncC conjugation genes. Structurally, AcaB consists of two helical hairpins in tandem which assemble into an anti-parallel four-helix bundle to form a two-stranded antiparallel beta-sheet positioned parallel to the helices. This is structurally similar to bacterial transcription factors from the ribbon-helix-helix (RHH) superfamily [1].

1: Comprehensive analysis of IncC plasmid conjugation identifies a crucial role for the transcriptional regulator AcaB. Hancock SJ, Phan MD, Luo Z, Lo AW, Peters KM, Nhu NTK, Forde BM, Whitfield J, Yang J, Strugnell RA, Paterson DL, Walsh TR, Kobe B, Beatson SA, Schembri MA; Nat Microbiol. 2020; [Epub ahead of print] PMID:32807890