The chemoreceptor zinc-binding domain (CZB) is found in bacterial signal transduction proteins - most frequently receptors involved in chemotaxis and motility, but also in c-di-GMP signalling and nitrate/nitrite-sensing. Originally discovered in the cytoplasmic chemoreceptor TlpD from Helicobacter pylori, it is often found C-terminal to the MCPsignal domain in cytoplasmic chemoreceptor proteins. The CZB domain contains a core sequence motif, Hxx[WFYL]x21-28Cx[LFMVI]Gx[WFLVI]x18-27HxxxH. The highly-conserved H-C-H-H residues of this motif are believed to coordinate zinc; mutating the latter two histidines of the motif to alanines abolishes Zn binding. This domain binds zinc with high affinity, with a Kd in the femtomolar range. This domain has been shown in E. coli to be a zinc sensor that regulates the catalytic activity of Pfam:PF00990 [2]. This domain also binds the chemoattractant HOCl at a site very close to that of zinc. It has been shown that zinc participates in HOCl sensing by forming a redox 'Cys-Zn switch' that reacts towards HOCl (Matilla et. al.,FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: Identification of a chemoreceptor zinc-binding domain common to cytoplasmic bacterial chemoreceptors. Draper J, Karplus K, Ottemann KM; J Bacteriol. 2011;193:4338-4345. PMID:21725005

2: Structure and signaling mechanism of a zinc-sensory diguanylate cyclase. Zahringer F, Lacanna E, Jenal U, Schirmer T, Boehm A; Structure. 2013;21:1149-1157. PMID:23769666