Small Subunit Of Serine Palmitoyltransferase A (SSSPTA)

The deduced 71-amino acid SSSPTA peptide contains 2 predicted transmembrane spans and shares 45% identity with SSSPTB, with most similarity in a central 28-amino acid domain that overlaps transmembrane span 2. Neither SSSPTA nor SSSPTB shares sequence similarity with yeast Tsc3. Database analysis revealed close orthologs of human SSSPTs in several vertebrate species.

SSSPTA interacted directly with SPTLC1, even in the absence of SPTLC2. Use of a panel of acyl-CoA substrates and different SPT subunit combinations revealed that different SPT isozymes had specific substrate preferences. The most active and selective isozyme combination was SPTLC1-SPTLC2-SSSPTA, which had strong preference for C16-CoA.