Proton-coupled sialic acid co-transport Authored: Jassal, B, 2009-07-06 Edited: Jassal, B, 2009-07-06 Pubmed10581036 Pubmed10947946 Pubmed11751519 Reactome Database ID Release 43428585 Reactome, http://www.reactome.org ReactomeREACT_19297 Reviewed: He, L, 2009-08-24 SLC17A5 encodes a lysosomal sialic acid transporter, Sialin (AST, membrane glycoprotein HP59) (Verheijen FW et al, 1999; Fu C et al, 2001). Lysosomes export sialic acid which is derived from the degradation of glycosylated membrane proteins. This export is dependent in the proton electrochemical gradient across the lysosomal membrane. It is present in the pathological tumor vasculature of the lung, breast, colon, and ovary, but not in the normal vasculature, suggesting that the protein may be critical to pathological angiogenesis. Sialin is not expressed in a variety of normal tissues, but is significantly expressed in human fetal lung. Defects in SLC17A5 cause Salla disease (SD) and infantile sialic acid storage disorder (ISSD, also called N-acetylneuraminic acid storage disease (NSD)). Both are sialic acid storage diseases (SASDs) which are autosomal recessive neurodegenerative disorders characterized by hypotonia, cerebellar ataxia and mental retardation in very young infants (Verheijen FW et al, 1999; Aula N et al, 2000).