Dimeric and tetrameric forms of catalytically active transmembrane CD38 in transfected HeLa cells.
CD38, a type II transmembrane glycoprotein, behaves as a catalytically active transporter responsible for ectocellular generation of cyclic ADP-ribose (cADPR) from NAD+ and for subsequent influx of cADPR across membranes [Franco, L., Guida, L., Bruzzone, S., Zocchi, E., Usai, C. and De Flora, A. (1998) FASEB J. in press]. cADPR regulates intracellular calcium homeostasis by releasing calcium from responsive stores. The cADPR-transporting function of CD38 requires channel-generating oligomeric forms of the protein rather than the 46 kDa monomers that have been described so far in CD38+ cells. Here we demonstrate that CD38, both in reconstituted proteoliposomes and in CD38-transfected HeLa cells, is a mixture of catalytically active monomers, homodimers and homotetramers. A soluble recombinant form of CD38 corresponding to its ectocellular region proved to be monomeric. Thus, association of native CD38 with either artificial or natural membranes seems to result in a reversible juxtaposition of monomers suitable to cADPR-transporting activity.
Bruzzone
S
S
Institute of Biochemistry, University of Genoa, Italy.
Guida
L
L
Franco
L
L
Zocchi
E
E
Corte
G
G
De Flora
A
A
D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001048:Aplysia / Q000201:enzymology; D002462:Cell Membrane / Q000378:metabolism; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D008081:Liposomes; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009244:NAD+ Nucleosidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011510:Proteolipids / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D014162:Transfection
D015703:Antigens, CD; D000943:Antigens, Differentiation; D008081:Liposomes; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D009097:Multienzyme Complexes; D011510:Proteolipids; D011994:Recombinant Proteins; C020485:proteoliposomes; D009243:NAD; D036541:ADP-ribosyl Cyclase; C498154:CD38 protein, human; D009244:NAD+ Nucleosidase; D051997:ADP-ribosyl Cyclase 1