Polar residues in a conserved motif spanning helices 1 and 2 are functionally important in the SulP transporter family.
The SulP family (including the SLC26 family) is a diverse family of anion transporters found in all domains of life, with different members transporting different anions. We used sequence and bioinformatics analysis of helices 1 and 2 of SulP family members to identify a conserved motif, extending the previously defined 'sulfate transporter motif'. The analysis showed that in addition to being highly conserved in both sequence and spacing, helices 1 and 2 contain a significant number of polar residues and are predicted to be buried within the protein interior, with at least some faces packed closely against other helices. This suggests a significant functional role for this region and we tested this by mutating polar residues in helices 1 and 2 in the sulfate transporter, SHST1. All mutations made, even those removing only a single hydroxyl group, had significant effects on transport. Many mutations abolished transport without affecting plasma membrane expression of the mutant protein, suggesting a functional role for these residues. Different helical faces appear to have different roles, with the most severe effects being localised to two interacting faces of helices 1 and 2. Our results confirm the predicted importance of conserved polar residues in helices 1 and 2 and suggest that transport of sulfate by SHST1 is dependent on a network of polar and aromatic interactions between these two helices.
Leves
Fiona P
FP
School of Biochemistry and Molecular Biology, Australian National University, Canberra, ACT 0200, Australia.
Tierney
M Louise
ML
Howitt
Susan M
SM
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D027321:Anion Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019295:Computational Biology; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D000076988:Sulfate Transporters; D013431:Sulfates / Q000378:metabolism
D000596:Amino Acids; D027321:Anion Transport Proteins; D010940:Plant Proteins; C089651:SLC26A2 protein, human; D000076988:Sulfate Transporters; D013431:Sulfates