Grimaldi J C, Balasubramanian S, Kabra N H, Shanafelt A, Bazan J F, Zurawski G, Howard M C
DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304, USA.
J Immunol. 1995 Jul 15;155(2):811-7.
The lymphocyte cell-surface Ag CD38 catabolizes NAD to adenosine 5' diphosphoribose (ADPR) and cyclic ADPR (cADPR). We show here that the soluble extracellular domain of CD38 (sCD38) mediates ADP ribosylation of several proteins. This was demonstrated by mass spectrometric analyses which revealed the addition of mass in units of 541.1 Da to these proteins, presumably corresponding to the covalent attachment of one or more ADPR moieties. Separate experiments showed that the same proteins became specifically radiolabeled following incubation with [32P]NAD plus sCD38. Additionally, it is shown that sCD38 can autoribosylate. Moreover, sCD38-mediated protein ribosylation was found to occur specifically at cysteine residues, since it was effectively blocked by addition of L-cysteine but not by other amino acids, and CD38-mediated protein ribosylation could be reversed by the addition of HgCl2, which specifically cleaves thiol-glycosidic bonds. ADPR purified from the reaction of sCD38 with NAD could itself be covalently transferred to target proteins at rates similar to the sCD38-mediated reaction, indicating that the ribosylation proceeds via the generation of this reactive intermediate. In vitro mutagenesis of a catalytic Glu residue that is conserved in numerous ADP-ribosyl transferases revealed that this amino acid is also important for catalysis in CD38. These data suggest that CD38 has the potential to cause ribosylation of experimental proteins, and raises the possibility that its specific ribosylation of a currently unidentified lymphocyte protein may contribute to its array of immunoregulatory activities.
淋巴细胞表面抗原CD38可将NAD分解为5'-二磷酸腺苷核糖（ADPR）和环化ADPR（cADPR）。我们在此表明，CD38的可溶性细胞外结构域（sCD38）介导几种蛋白质的ADP核糖基化。质谱分析证实了这一点，该分析显示这些蛋白质的质量以541.1 Da为单位增加，推测这对应于一个或多个ADPR部分的共价连接。单独的实验表明，与[32P]NAD加sCD38孵育后，相同的蛋白质会被特异性放射性标记。此外，研究表明sCD38可以自身进行核糖基化。而且，发现sCD38介导的蛋白质核糖基化特异性发生在半胱氨酸残基上，因为添加L-半胱氨酸可有效阻断该过程，而其他氨基酸则不能，并且添加HgCl2可逆转CD38介导的蛋白质核糖基化，HgCl2可特异性切割硫醇糖苷键。从sCD38与NAD的反应中纯化得到的ADPR本身可以以与sCD38介导的反应相似的速率共价转移到靶蛋白上，这表明核糖基化是通过生成这种反应性中间体进行的。对众多ADP-核糖基转移酶中保守的催化性Glu残基进行体外诱变，结果表明该氨基酸对CD38的催化作用也很重要。这些数据表明CD38有可能导致实验性蛋白质的核糖基化，并增加了一种可能性，即其对目前尚未鉴定的淋巴细胞蛋白质的特异性核糖基化可能有助于其一系列免疫调节活性。
