Kinetic competence of the cADP-ribose-CD38 complex as an intermediate in the CD38/NAD+ glycohydrolase-catalysed reactions: implication for CD38 signalling.
CD38/NAD(+) glycohydrolase is a type II transmembrane glycoprotein widely used to study T- and B-cell activation and differentiation. CD38 is endowed with two different activities: it is a signal transduction molecule and an ectoenzyme that converts NAD(+) into ADP-ribose (NAD(+) glycohydrolase activity) and small proportions of cADP-ribose (cADPR; ADP-ribosyl cyclase activity), a calcium-mobilizing metabolite, which, ultimately, can also be hydrolysed (cADPR hydrolase activity). The relationship between these two properties, and strikingly the requirement for signalling in the formation of free or enzyme-complexed cADPR, is still ill-defined. In the present study we wanted to test whether the CD38-cADPR complex is kinetically competent in the conversion of NAD(+) into the reaction product ADP-ribose. In principle, such a complex could be invoked for cross-talk, via conformational changes, with neighbouring partner(s) of CD38 thus triggering the signalling phenomena. Analysis of the kinetic parameters measured for the CD38/NAD(+) glycohydrolase-catalysed hydrolysis of 2'-deoxy-2'-aminoribo-NAD(+) and ADP-cyclo[N1,C1']-2'-deoxy-2'-aminoribose (slowly hydrolysable analogues of NAD(+) and cADPR respectively) ruled out that the CD38-cADPR complex can accumulate under steady-state conditions. This was borne out by simulation of the prevalent kinetic mechanism of CD38, which involve the partitioning of a common E.ADP-ribosyl intermediate in the formation of the enzyme-catalysed reaction products. Using this mechanism, microscopic rate conditions were found which transform a NAD(+) glycohydrolase into an ADP-ribosyl cyclase. Altogether, the present work shows that if the cross-talk with a partner depends on a conformational change of CD38, this is most probably not attributable to the formation of the CD38-cADPR complex. In line with recent results on the conformational change triggered by CD38 ligands [Berthelier, Laboureau, Boulla, Schuber and Deterre (2000) Eur. J. Biochem. 267, 3056-3064], we believe that the Michaelis CD38-NAD(+) complex could play such a role instead.
Cakir-Kiefer
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C
Laboratoire de Chimie Bioorganique, UMR 7514 CNRS-ULP, Faculté de Pharmacie, 74 route du Rhin, 67400 Strasbourg-Illkirch, France.
Muller-Steffner
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Oppenheimer
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N
Schuber
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F
D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000378:metabolism*; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000378:metabolism* / Q000502:physiology*; D002384:Catalysis; D002417:Cattle; D036563:Cyclic ADP-Ribose; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D009243:NAD / Q000031:analogs & derivatives / Q000378:metabolism; D009244:NAD+ Nucleosidase / Q000378:metabolism* / Q000502:physiology*; D015398:Signal Transduction
C435928:2'-deoxy-2'-aminoribo-NAD; C435929:ADP-cyclo(N1,C1')-2'-deoxy-2'-aminoribose; D015703:Antigens, CD; D000943:Antigens, Differentiation; D046911:Macromolecular Substances; D009243:NAD; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D036541:ADP-ribosyl Cyclase; D009244:NAD+ Nucleosidase; D051997:ADP-ribosyl Cyclase 1