Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.


Sci. Signal., 11 September 2012
Vol. 5, Issue 241, p. ra67
[DOI: 10.1126/scisignal.2002700]


The Membrane-Bound Enzyme CD38 Exists in Two Opposing Orientations

Yong Juan Zhao*, Connie Mo Ching Lam*, and Hon Cheung Lee{dagger}

Department of Physiology, Li Ka Shing School of Medicine, The University of Hong Kong, Hong Kong, China.

* These authors contributed equally to this work.

Abstract: The transmembrane enzyme CD38, a multifunctional protein ubiquitously present in cells, is the main enzyme that synthesizes and hydrolyzes cyclic adenosine 5'-diphosphate-ribose (cADPR), an intracellular Ca2+-mobilizing messenger. CD38 is thought to be a type II transmembrane protein with its carboxyl-terminal catalytic domain located on the outside of the cell; thus, the mechanism by which CD38 metabolizes intracellular cADPR has been controversial. We developed specific antibodies against the amino-terminal segment of CD38 and showed that two opposing orientations of CD38, type II and type III (which has its catalytic domain inside the cell), were both present on the surface of HL-60 cells during retinoic acid–induced differentiation. When activated by interferon-{gamma}, human primary monocytes and the monocytic U937 cell line exhibited a similar co-distribution pattern. Site-directed mutagenesis experiments showed that the membrane orientation of CD38 could be converted from a mixture of type II and type III orientations to all type III by mutating the cationic amino acid residues in the amino-terminal segment of CD38. Expression of type III CD38 construct in transfected cells led to increased intracellular concentrations of cADPR, indicating the importance of the type III orientation of CD38 to its Ca2+ signaling function. The identification of these two forms of CD38 suggests that flipping the catalytic domain from the outside to the inside of the cell may be a mechanism regulating its signaling activity.

{dagger} To whom correspondence should be addressed. E-mail: leehc{at}

Citation: Y. J. Zhao, C. M. C. Lam, H. C. Lee, The Membrane-Bound Enzyme CD38 Exists in Two Opposing Orientations. Sci. Signal. 5, ra67 (2012).

Read the Full Text

CD38 Controls the Innate Immune Response against Listeria monocytogenes.
T. Lischke, K. Heesch, V. Schumacher, M. Schneider, F. Haag, F. Koch-Nolte, and H.-W. Mittrucker (2013)
Infect. Immun. 81, 4091-4099
   Abstract »    Full Text »    PDF »
In vitro reconstitution of lipid-dependent dual topology and postassembly topological switching of a membrane protein.
H. Vitrac, M. Bogdanov, and W. Dowhan (2013)
PNAS 110, 9338-9343
   Abstract »    Full Text »    PDF »

To Advertise     Find Products

Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882