{PDOC00680}
{PS00872; NA_GALACTOSIDE_SYMP}
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* Sodium:galactoside symporter family signature *
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It has  been shown [1] that integral membrane proteins that mediate the intake
of a  wide  variety  of  molecules  with the concomitant uptake of sodium ions
(sodium symporters)  can  be  grouped, on the basis of sequence and functional
similarities into  a  number  of  distinct  families. One of these families is
known as the  sodium:galactoside symporter family (SGF) and currently consists
of the following proteins:

 - The  melibiose  carrier  (gene melB) from a variety of enterobacteria. This
   protein is  responsible  for  melibiose  transport  and is capable of using
   hydrogen, sodium, and lithium cations as coupling cations for cotransport.
 - The  lactose  permease from Lactobacillus (gene lacS or lacY). This protein
   is responsible  for  the transport of beta-galactosides into the cell, with
   the concomitant   export  of  a  proton.  It  consists of two domains; a N-
   terminal SGF  domain  and a C-terminal domain that resembles that of enzyme
   IIA of the PEP:sugar phosphotransferase system.
 - The raffinose permease from Pediococcus pentosaceus.  It also consists of a
   N-terminal SGF domain and a C-terminal IIA domain.
 - The glucuronide carrier (gene gusB or uidP) from Escherichia coli.
 - The xylose transporter (gene xylP) from Lactobacillus pentosus.
 - Escherichia coli hypothetical protein yagG.
 - Escherichia coli hypothetical protein yicJ.
 - Escherichia coli hypothetical protein yihO.
 - Escherichia coli hypothetical protein yihP.
 - Bacillus subtilis hypothetical protein yjmB.
 - Bacillus subtilis hypothetical protein ynaJ.

Like sugar transport  proteins, these integral membrane proteins are predicted
to comprise    twelve  membrane  spanning  domains.  As a signature pattern we
selected a  highly  conserved  region  which  is located in a cytoplasmic loop
between  the second  and third transmembrane regions.  This region starts with
a conserved  aspartate which has been shown [2], in melB, to  be important for
the activity of the protein.

-Consensus pattern: [DG]-x(3)-G-x(3)-[DN]-x(6,8)-[GA]-[KRHQ]-[FSAR]-[KRL]-
                    [PT]-[FYW]-[LIVMWQ]-[LIV]-x(0,1)-[GAFV]-[GSTA]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2004 / Pattern and text revised.

[ 1] Reizer J., Reizer A., Saier M.H. Jr.
     "A functional superfamily of sodium/solute symporters."
     Biochim. Biophys. Acta 1197:133-166(1994).
     PubMed=8031825
[ 2] Pourcher T., Deckert M., Bassilana M., Leblanc G.
     "Melibiose permease of Escherichia coli: mutation of aspartic acid 55
     in putative helix II abolishes activation of sugar binding by Na+
     ions."
     Biochem. Biophys. Res. Commun. 178:1176-1181(1991).
     PubMed=1872836

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