INHIBITION OF NAD(-RIBOSYL CYCLASE ACTIVITIES OF LEUKOCYTE CELL-SURFACE ANTIGEN CD38 BY GANGLIOSIDES() GLYCOHYDROLASE AND ADP)

We have recently reported that gangliosides act as inhibitors of ADP-r ibosyltransferases and NAD(+) glycohydrolases (NADase) of pertussis to xin and the C3 exoenzyme from Clostridium botulinum (Hara-Yokoyama, M. , Hirabayashi, Y., Irie, F., Syuto, B., Moriishi, H., Susya, H., and F uruyama, S. (1995) J. Biol. Chem. 270, 8115-8121). Here, we investigat ed the effect of gangliosides on the enzymatic activity of leukocyte c ell surface antigen CD38, which is identified as an ecto-NADase (Konta ni, K., Nishina, H., Ohoka, Y., Takahashi, K., and Katada, T. (1993) J . Biol. Chem. 268, 16895-16898). Gangliosides G(M1a) and G(Q1b alpha) inhibited the NADase activity in the immunoprecipitate of anti-CD38 an tibody from the membrane extract of retinoic acid-treated human leukem ic HL-60 cells. Gangliosides also inhibited the NADase activity of the extracellular domain of CD38 antigen that was deprived of the transme mbrane domain and was expressed in Escherichia coli as a fusion protei n with maltose-binding protein (MBP-CD38). The order of the inhibitory effect of purified ganglioside species on the NADase activity on MBP- CD38 was as follows: G(Q1b alpha) > G(T1b), G(Q1b) > G(D1a), G(D1b), G (M1a),G(M1b), G(D3), G(M3). G(Q1b alpha) inhibited the NADase of MBP-C D38 in a noncompetitive manner versus NAD(+) with a K-i value of about 0.3 mu M. Neither ceramide nor the oligosaccharide moiety of G(Q1b al pha) had an effect on the NADase activity. G(Q1b alpha) G(T1b), and G( Q1b) also efficiently inhibited the ADP-ribosyl cyclase activity of MB P-CD38. At present, gangliosides are the only endogenous species that can block the enzymatic activity of CD38 antigen. The present results suggest a potential role of gangliosides as inhibitors of the ecto-NAD ases.