CD38 in Bovine Lung: A Multicatalytic NADase

Population variability in CD38 activity: correlation with age and significant effect of TNF-α -308G>A and CD38 184C>G SNPs

CD38 (EC 3.2.2.6, NAD(+)-glycohydrolase) is a multifunctional enzyme catalyzing the synthesis and hydrolysis of cyclic ADP-ribose from NAD(+) to ADP-ribose. The loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications. Notably, it has been linked to HIV infection, leukemias, myelomas, solid tumors, Type II Diabetes mellitus, bone metabolism, as well as Autism Spectrum Disorder. Taking into account the crucial role played by CD38 in many diseases and in clinical practice, here we assessed the distribution of CD38 NADase activity in a healthy population (104 sex-matched unrelated individuals, 12-98 years) and determined its main predictors among genetic and physiological factors (age and sex). The mean value of CD38 NADase activity was 0.051±0.023 mU/mg (0.010-0.099 mU/mg), following a normal distribution in the study population (Kolmogorov-Smirnov test P=0.200). The TNF-α -308G>A (rs1800629) resulted the main predictor (β=0.364, P=0.00008), followed by Age (β=0.280, P=0.002) and the CD38 184C>G (rs6449182) (β=0.193, P=0.033). Our study contributes to understanding CD38 enzyme physiological functions, by reporting, for the first time, its activity distribution in healthy individuals and demonstrating a significant positive correlation with age. Moreover, the possible use of TNF-α -308G>A (rs1800629) and the CD38 184C>G (rs6449182) SNPs as predictive genetic markers of CD38 activity, clearly point toward possible pharmacogenomic applications and to a more refined use of CD38 in clinical settings.

Cu(ii)- and disulfide bonds-induced stabilization during the guanidine hydrochloride- and thermal-induced denaturation of NAD-glycohydrolase from the venom of Agkistrodon acutus

NAD-glycohydrolase (AA-NADase) from Agkistrodon acutus venom is a unique multicatalytic enzyme with both NADase and AT(D)Pase-like activities. Among all identified NADases, only AA-NADase is a disulfide-linked dimer and contains Cu(2+). Cu(2+) and disulfide bonds are essential for its multicatalytic activity. In this study, the effects of Cu(2+) and disulfide-bonds on guanidine hydrochloride (GdnHCl)- and thermal-induced unfolding of AA-NADase have been investigated by fluorescence, circular dichroism (CD) and differential scanning calorimetry (DSC). Cu(2+) and disulfide bonds not only increase the free energy change during the GdnHCl-induced unfolding as determined by fluorescence, but also increase the overall enthalpy change and the transition temperature during the thermal-induced unfolding as determined by CD and DSC. The slope of the GdnHCl-induced unfolding curve at its midpoint and the heat capacity of thermal-induced unfolding are slightly affected by Cu(2+) but significantly decrease after reduction of three disulfide-bonds. This work suggests that Cu(2+) stabilizes the folded state by increasing the enthalpy of unfolding, while disulfide-bonds stabilize the folded state by increasing the enthalpy of unfolding and stabilizing the packing of hydrophobic residues. Thus both Cu(2+) and disulfide bonds play a structural role in its multicatalytic activity.

Metal ions binding to NAD-glycohydrolase from the venom of Agkistrodon acutus: regulation of multicatalytic activity

AA-NADase from Agkistrodon acutus venom is a unique multicatalytic enzyme with both NADase and AT(D)Pase activities. Among all identified NADases, only AA-NADase contains Cu(2+) ions that are essential for its multicatalytic activity. In this study, the interactions between divalent metal ions and AA-NADase and the effects of metal ions on its structure and activity have been investigated by equilibrium dialysis, isothermal titration calorimetry, fluorescence, circular dichroism, dynamic light scattering and HPLC. The results show that AA-NADase has two classes of Cu(2+) binding sites, one activator site with high affinity and approximately six inhibitor sites with low affinity. Cu(2+) ions function as a switch for its NADase activity. In addition, AA-NADase has one Mn(2+) binding site, one Zn(2+) binding site, one strong and two weak Co(2+) binding sites, and two strong and six weak Ni(2+) binding sites. Metal ion binding affinities follow the trend Cu(2+) > Ni(2+) > Mn(2+) > Co(2+) > Zn(2+), which accounts for the existence of one Cu(2+) in the purified AA-NADase. Both NADase and ADPase activities of AA-NADase do not have an absolute requirement for Cu(2+), and all tested metal ions activate its NADase and ADPase activities and the activation capacity follows the trend Zn(2+) > Mn(2+) > Cu(2+) ~Co(2+) > Ni(2+). Metal ions serve as regulators for its multicatalytic activity. Although all tested metal ions have no obvious effects on the global structure of AA-NADase, Cu(2+)- and Zn(2+)-induced conformational changes around some Trp residues have been observed. Interestingly, each tested metal ion has a very similar activation of both NADase and ADPase activities, suggesting that the two different activities probably occur at the same site.