*8.A.79 The 3 TMS cyd* Operon Protein, CydX (CydX) Family** cydX (ybgE) is a gene within the cyd operon of E. coli. The encoded protein has 97 aas and 3 TMSs and is essential for CydAB function (VanOrsdel et al. 2013). Homologues in other organisms have the same or a similar topology. It is requried for the assembly and stability of the diheme active site (Hoeser et al. 2014). It may play a role in a functional interaction with the CydA Q-loop, an enigmatic domain of the cytochrome bd oxidase complex (Allen et al. 2014).
References:
Allen, R.J., E.P. Brenner, C.E. VanOrsdel, J.J. Hobson, D.J. Hearn, and M.R. Hemm. (2014). Conservation analysis of the CydX protein yields insights into small protein identification and evolution. BMC Genomics 15: 946.
Hoeser, J., S. Hong, G. Gehmann, R.B. Gennis, and T. Friedrich. (2014). Subunit CydX of Escherichia coli cytochrome bd ubiquinol oxidase is essential for assembly and stability of the di-heme active site. FEBS Lett. 588: 1537-1541.
VanOrsdel, C.E., S. Bhatt, R.J. Allen, E.P. Brenner, J.J. Hobson, A. Jamil, B.M. Haynes, A.M. Genson, and M.R. Hemm. (2013). The Escherichia coli CydX protein is a member of the CydAB cytochrome bd oxidase complex and is required for cytochrome bd oxidase activity. J. Bacteriol. 195: 3640-3650.
Examples:
TC#	Name	Organismal Type	Example
8.A.79.1.1	*The cyd* operon-encoded YbgE protein of 97 aas and 3 TMSs. It may be important for full activity of the CydAB cytochrome bd oxidase complex (VanOrsdel et al. 2013).**	Proteobacteria	YbgE of E. coli

8.A.79.1.2	YbgE homologue of 96 aas and 3 TMSs	Proteobacteria	YbgE homologue of Haemophilus ducreyi

8.A.79.1.3	YbgE homologue of 82 aas and 3 TMSs	Proteobacteria	YbgE homologue of Methylibium petroleiphilum