Transport of organic anions by the lysosomal sialic acid transporter: a functional approach towards the gene for sialic acid storage disease.

Transport of sialic acid through the lysosomal membrane is defective in the human sialic acid storage disease. The mammalian sialic acid carrier has a wide substrate specificity for acidic monosaccharides. Recently, we showed that also non-sugar monocarboxylates like L-lactate are substrates for the carrier. Here we report that other organic anions, which are substrates for carriers belonging to several anion transporter families, are recognized by the sialic acid transporter. Hence, the mammalian system reveals once more novel aspects of solute transport, including sugars and a wide array of non-sugar compounds, apparently unique to this system. These data suggest that the search for the sialic acid storage disease gene can be initiated by a functional selection of genes from a limited number of anion transporter families. Among these, candidates will be identified by mapping to the known sialic acid storage disease locus.