ADP-ribosylation Cycles

防御素，如人中性粒细胞肽（HNPs），通过多种作用促进先天免疫，包括杀死微生物；肺部对炎症的反应是高浓度的。精氨酸对于HNP的活性是至关重要的，它被鸟氨酸取代而降低。adp核糖基转移酶（ARTs）催化adp核糖从NAD转移到蛋白质底物中的受体精氨酸，而adp核糖基精氨酸水解酶释放adp核糖。气道上皮细胞表面的ART1在精氨酸14和精氨酸24上特异性地将HNP-1核糖化，adp核糖化改变了其生物活性。从哮喘和特发性肺纤维化（IPF）患者的支气管肺泡灌洗液（BALF）中分离到二和单adp -核糖基化的HNP-1，提示adp -核糖基化在疾病中的作用。在本研究中，我们在体外观察到art1催化的HNP-1的adp核糖基化产生了一个新的产物，adp核糖位于精氨酸24上，鸟氨酸取代了精氨酸14的位置。我们假设adp -核糖体精氨酸对产生鸟氨酸的非酶水解反应敏感。二或单adp -核糖体-HNP-1在37℃孵育时，adp -核糖体精氨酸部分被鸟氨酸取代，而在相同条件下孵育的未修饰的HNP-1的氨基酸分析和质谱分析未检测到鸟氨酸。此外，鸟氨酸是由模型化合物adp -核糖精氨酸产生的。来自IPF患者的半胱氨酸含有adp -核糖基- hnp -鸟氨酸，以及单和双adp -核糖基化的HNP-1，与体内精氨酸向鸟氨酸的转化一致。通过转移酶靶向adp核糖基化特定精氨酸，导致其被鸟氨酸取代，是通过翻译后修饰调节蛋白质功能的一种新的替代途径。

Defensins, e.g., human neutrophil peptides (HNPs), contribute to innate immunity through diverse actions including microbial killing; high concentrations are present in the lung in response to inflammation. Arginines are critical for HNP activity, which is decreased by their replacement with ornithine. ADP-ribosyltransferases (ARTs) catalyze transfer of ADP-ribose from NAD to an acceptor arginine in a protein substrate, whereas ADP-ribosylarginine hydrolases release ADP-ribose. ART1 on the surface of airway epithelial cells ADP-ribosylated HNP-1 specifically on arginines 14 and 24, with ADP-ribosylation altering biological activity. Di- and mono-ADP-ribosylated HNP-1 were isolated from bronchoalveolar lavage fluid (BALF) of patients with asthma and idiopathic pulmonary fibrosis (IPF), suggesting a role for ADP-ribosylation in disease. In the present study, we observed that ART1-catalyzed ADP-ribosylation of HNP-1 in vitro generated a novel product with ADP-ribose on arginine 24, and ornithine replacing arginine at position 14. We hypothesized that ADP-ribosylarginine is susceptible to a non-enzymatic hydrolytic reaction yielding ornithine. On incubation of di- or mono-ADP-ribosyl-HNP-1 at 37 C, ADP-ribosylarginine was partially replaced by ornithine, whereas ornithine was not detected by amino acid analysis and mass spectrometry of unmodified HNP-1 incubated under the same conditions. Further, ornithine was produced from the model compound, ADP-ribosylarginine. BALF from an IPF patient contained ADP-ribosyl-HNP-ornithine as well as mono- and di-ADP-ribosylated HNP-1, consistent with in vivo conversion of arginine to ornithine. Targeted ADP-ribosylation of specific arginines by transferases, resulting in their replacement with ornithine, is a novel alternative pathway for regulation of protein function through post-translational modification.