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Common Domain Found in Members of the MFS Drug: Hydrogen Antiporter-2 Family, Glycosyltransferases, and Magnesium-P-type ATPases


The Drug: H+ antiporter-2 (DHA2) family includes members belonging to the Major Facilitator Superfamily (MFS) whose members portray a topology of 14 transmembrane segments (TMSs) in a 6+2+6 TMS arrangement where the two 6 TMS segments are repeat units. This paper identifies a unique motif among members of the DHA2 family and two functionally diverse protein families. The three families share statistically significant sequence conservation containing 8 TMSs. This segment is found in the C-terminal half of the 14 TMS DHA2 proteins, the entire 8 TMS glycosyltranferses (GT) and the N-terminal 8 TMS fusion in some Mg2+-P-type ATPases. Binary sequence alignments using the GSAT program were used to statistically establish homology of these regions within the three families. This study postulates that the common element in these proteins all arose via the same pathway from an ancestral 3 TMS precursor unit, which duplicated to a 6 TMS unit, and diverged into topologically and functionally distinct families. DHA2 comparisons to the Mg2+-P-type ATPases and glycosyltransferases will provide the essential framework for the characterization of their functional properties.

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