The CHAD (conserved histidine α-helical domain) is an uncharacteriseddomain, with a characteristic pattern of conserved histidines and othercharged residues. It is predicted to adopt an α-helical fold. The sequenceconservation pattern suggests that this domain is likely to contain two repeatunits, with at least 4 helices each, at its core. The conserved chargedresidues could form a strongly polar surface that could participate, either inmetal chelation, or act as phosphoacceptors [].Some proteins known to contain a CHAD domain are listed below:Escherichia coli uncharacterised protein YgiF.Mycobacterium tuberculosis uncharacterised protein Rv2226/MT2285.
The CHAD (conserved histidine α-helical domain) is an uncharacteriseddomain, with a characteristic pattern of conserved histidines and othercharged residues. It is predicted to adopt an α-helical fold. The sequenceconservation pattern suggests that this domain is likely to contain two repeatunits, with at least 4 helices each, at its core. The conserved chargedresidues could form a strongly polar surface that could participate, either inmetal chelation, or act as phosphoacceptors [].
This group includes uncharacterised proteins from Methanosarcina spp. with CYTH and CHAD domains, and a central HD-like domain.CYTH domain proteins may play a central role in the interface between nucleotide and polyphosphate metabolism []. Based on the conservation of catalytic residues, CYTH domains are likely to chelate two divalent cations and exhibit a reaction mechanism that is dependent on two metal ions, analogous to nucleotide cyclases, polymerases, and certain phosphoesterases []. It has also been suggested that the experimentally characterised members of the CYTH domain superfamily, namely, adenylyl cyclase and thiamine triphosphatase, are secondary derivatives of proteins that performed an ancient role in polyphosphate and nucleotide metabolism [].The C-terminal CHAD domain () is an α-helical domain that is found fused to the CYTH domain or is encoded by genes occurring in the same operon as those encoding CYTH domains. Therefore, it is predicted to be functionally associated with CYTH adenylate cyclases []. While there is no experimental evidence as to the function of the CHAD domain, and no clear functional prediction can be made for it, the conserved histidines and other charged residues could form a strongly polar surface that could either participate in metal chelation, or act as phosphoacceptors [].Apart from these two domains, members of this group have a unique central domain. It is distantly related to the HD-type metal dependent phosphohydrolase domain (), but there is no indication as to its function.
