| Comment | The SulP family is a large and ubiquitous family with over 30 sequenced members derived from bacteria, fungi, plants and
animals. Many organisms including Bacillus subtilis, Synechocystis sp, Saccharomyces cerevisiae, Arabidopsis thaliana and
Caenorhabditis elegans possess multiple SulP family paralogues. Many of these proteins are functionally characterized, and all
are sulfate uptake transporters. Some transport their substrate with high affinities, while others transport it with relatively low
affinities. Most function by SO42- :H+symport, but SO42- :HCO3- antiport has been reported for the rat protein (spP45380).
The bacterial proteins vary in size from 434 residues to 566 residues with one exception, a Mycobacterium tuberculosis protein
with 784 residues. The eukaryotic proteins vary in size from 611 residues to 893 residues with one exception, a protein
designated "early nodulin 70 protein" from Glycine max which is reported to be of 485 residues. Thus, the eukaryotic proteins are
almost without exception larger than the prokaryotic proteins. These proteins exhibit 10-13 putative transmembrane a-helical
spanners (TMSs) depending on the protein.
The phylogenetic tree for the SulP family reveals five principal branches. Three of these are bacterial specific as follows: one
bears a single protein from M. tuberculosis; a second bears two proteins, one from M. tuberculosis, the other from Synechocystis
sp, and the third bears all remaining prokaryotic proteins. The remaining two clusters bear only eukaryotic proteins with the
animal proteins all localized to one branch and the plant and fungal proteins localized to the other.
The generalized transport reactions catalyzed by SulP family proteins are:
(1) SO42- (out) + nH+ (out) --> SO42- (in) + nH+ (in).
(2) SO42- (out) + nHCO3- (in) SO42- (in) + nHCO3- (out). |
