Functional role of glycosylation on the recombinant CD38/ADP-ribosyl cyclase in CHO cells

Abstract

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 V max 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.