d-Amino acid-containing peptides (DAACPs) make up a class of post-translationally modified peptides in animals that play important roles as cell-to-cell signaling molecules. Despite the functional importance of l- to d-residue isomerization, little is known about its prevalence, mostly due to difficulties associated with detecting differences in peptide stereochemistry. Prior efforts to discover DAACPs have been largely focused on pursuing peptides based on homology to known DAACPs or DAACP-encoding precursors. Here, we used a combination of enzymatic screening, mass spectrometry, and chromatographic analysis to identify novel DAACPs in the central nervous system (CNS) of Aplysia californica. We identified five new DAACPs from the pleurin precursor and three DAACPs from previously uncharacterized proteins. In addition, two peptides from the pleurin precursor, Plrn2 and Plrn3, exist as DAACPs with the d-residue found at position 2 or 3. These differentially modified forms of Plrn2 and Plrn3 are located in specific regions of the animal's CNS. Plrn2 and Plrn3 appear to be the first animal DAACPs in which the d-residue is found at more than one position, and this suggests that l- to d-residue isomerization may be a more variable/dynamic modification than previously thought. Overall, this study demonstrates the utility of nontargeted DAACP discovery approaches for identifying new DAACPs and demonstrates that isomerization is prevalent throughout the CNS of A. californica.

中文翻译：

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在加州海Ap的神经肽之间发现差异翻译后氨基酸异构化。

含有d-氨基酸的肽（DAACP）构成了动物中一类经过翻译后修饰的肽，它们在细胞间信号分子中起着重要的作用。尽管从l到d残基异构化具有重要的功能，但对其流行率知之甚少，主要是由于与检测肽立体化学差异有关的困难。发现DAACP的先前努力主要集中在基于与已知DAACP或编码DAACP的前体同源的肽上。在这里，我们结合使用了酶促筛查，质谱分析和色谱分析，以鉴定出加州Ap的中枢神经系统（CNS）中的新型DAACP。我们从胸膜前体中鉴定出五个新的DAACP，并从以前未鉴定的蛋白质中鉴定出三个DAACP。此外，胸膜素前体的两个肽Plrn2和Plrn3作为DAACP存在，d残基位于2或3位。这些Plrn2和Plrn3的差异修饰形式位于动物CNS的特定区域。Plrn2和Plrn3似乎是第一个在多个位置发现d-残基的动物DAACP，这表明从l到d残基的异构化可能比以前认为的更具可变性/动态性。总体而言，这项研究证明了非靶向DAACP发现方法在鉴定新DAACP方面的​​实用性，并证明了异构化在加利福尼亚州立农杆菌的整个中枢神经系统中普遍存在。Plrn2和Plrn3的这些差异修饰的形式位于动物的中枢神经系统的特定区域。Plrn2和Plrn3似乎是第一个在多个位置发现d-残基的动物DAACP，这表明从l到d残基的异构化可能比以前认为的更具可变性/动态性。总的来说，这项研究证明了非靶向DAACP发现方法在鉴定新DAACP方面的​​实用性，并证明了异构化在加利福尼亚州立农杆菌的整个中枢神经系统中普遍存在。Plrn2和Plrn3的这些差异修饰的形式位于动物的中枢神经系统的特定区域。Plrn2和Plrn3似乎是第一个在多个位置发现d-残基的动物DAACP，这表明从l到d残基的异构化可能比以前认为的更具可变性/动态性。总的来说，这项研究证明了非靶向DAACP发现方法在鉴定新DAACP方面的​​实用性，并证明了异构化在加利福尼亚州立农杆菌的整个中枢神经系统中普遍存在。