Chidambaram N, Chang C F
Department of Biochemistry, Faculty of Medicine, National University of Singapore, Singapore.
Int J Biochem Cell Biol. 1998 Sep;30(9):1011-8. doi: 10.1016/s1357-2725(98)00057-0.
Current evidence suggests that CD38, a lymphocyte differentiation antigen, has been found to be functionally indistinguishable from the native form when it was expressed as a soluble and non-glycosylated protein in yeast. Studies were conducted to evaluate the functional role of glycosylation on the membrane-bound CD38 in mammalian cells. The stable transformants of CHO cells were established with pXJ41-CD38 construct and the recombinant CD38 was detected at the surface of CHO cells using a polyclonal antibody to rat CD38 by immunocytochemistry. The recombinant protein displaying ADP-ribosyl cyclase activity was purified from CHO cells, which appeared as 42 and 46 kDa bands on immunoblot under non-reducing and reducing conditions, respectively. The recombinant CD38 was then subjected to deglycosylation with N-glycosidase F that resulted in a 33 kDa band on immunoblot under reducing condition. Further the partial deglycosylation of the recombinant CD38, performed at various time intervals, resulted in a series of bands (33-46 kDa) on immunoblot. Kinetic analysis indicated that deglycosylation of the recombinant CD38 showed a considerable decrease in Vmax and an increase in K(m) of ADP-ribosyl cyclase activity. These observations clearly suggest that glycosylation plays an important role to maintain the enzymatic activity and substrate affinity of CD38/ADP-ribosyl cyclase for mediating the signalling events in mammalian cells.
