The VSFASSQQ motif confers calcium sensitivity to the intracellular apyrase LALP70

BACKGROUND: Apyrases are divalent ion dependent tri- and dinucleotide phosphatases with different substrate specificity. The intracellular lysosomal apyrase LALP70 is also expressed as a splice variant (LALP70v) lacking a VSFASSQQ motif in the center of the molecule (aminoacids 287–294). However, the functional significance of this motif is unknown. In this report we used a thin layer chromatography approach to study separately the UTPase and UDPase activity of the two LALP-enzymes. RESULTS: We show, that LALP70 and LALP70v cleaved UTP to UDP in a calcium independent manner. In contrast, the cleavage of UDP to UMP was strongly calcium dependent for LALP70, but calcium independent for LALP70v. CONCLUSIONS: The VSFASSQQ motif not only influences the substrate specificity of LALP70, but it confers calcium sensitivity to LALP70 during the UDP cleavage. Whether this is due to direct binding of calcium to this motif or to a conformational change of the enzyme, remains to be elucidated.