9.B.36 The Acid Resistance Membrane Protein (HdeD) Family
The HdeD protein of E. coli is a 190 aa protein required for induction of acid resistance in response to overexpression of the AraC-type regulator, YdeO (Masuda and Church, 2003). It has 6 TMSs in a 2 + 2 + 2 arrangement. Evidence for an internally triplicated 2 TMS element was found. This protein may function with a 194 aa, 2 TMS protein (gi #3288672).
Homologues of HdeD include the DR3 protein of the moss, Tortula rutalis (223 aas; AAN87348) which also has 6 putative TMSs. Other homologues are annotated 'putative permease.' Homologues are generally of 160-240 aas in length with 6 TMSs in a 2 + 2 + 2 arrangement. They derive from proteobacteria, cyanobacteria, plants, myxobacteria, low and high G C Gram-positive bacteria and archaea. Some are much bigger (>450 aas) due to the presence of large hydrophilic extensions.