The sea urchin is an extensively used model system for the study of calcium signalling by the messenger molecules NAADP and cyclic ADP-ribose. Both are synthesized by ADP-ribosyl cyclases but our molecular understanding of these enzymes in the sea urchin is limited. We have recently reported the cloning of an extended family of sea urchin ADP-ribosyl cyclases and shown that one of these enzymes (SpARC1) is active within the endoplasmic reticulum lumen. These studies suggest that production of messengers is compartmentalized. Here we characterize the properties of SpARC2. SpARC2 catalyzed both NAADP and cyclic ADP-ribose production. Unusually, the NAD surrogate, NGD was a poor substrate. In contrast to SpARC1, heterologously expressed SpARC2 localized to the plasma membrane via a glycosylphosphatidylinositol (GPI)-anchor. Transcripts for SpARC2 were readily detectable in sea urchin eggs and a majority of the endogenous membrane bound activity was found to be GPI-anchored. Our data reveal striking differences in the properties of sea urchin ADP-ribosyl cyclases and provide further evidence that messenger production may occur outside of the cytosol.
Bibliographical noteFunding Information:
We thank Masa Tada (University College London), Gary Wessel (Brown University) and Frances Lund (Trudeau Institute) for provision of reagents and Caroline Dalton, Robert Hooper and Chi Li for useful discussions. This work was supported by BBSRC grants BB/D018110/1 (DC & SP) and BBS/B/0661X (TJG & LD), NIH grants HD12986 (VDD) and NS046783 (MJB & JSM), and NSF grant 0237946 (MJB & JSM).
- ADP-ribosyl cyclases
- Cyclic ADP-ribose
- Sea urchin