Loo Shining, Kam Antony, Xiao Tianshu, Tam James P
School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
Front Plant Sci. 2017 Dec 22;8:2162. doi: 10.3389/fpls.2017.02162. eCollection 2017.
Cysteine-rich peptides (CRPs) play important host-defense roles in plants. However, information concerning CRPs in the Cactaceae (cactus) family is limited, with only a single cactus-derived CRP described to date. Here, we report the identification of 15 novel CRPs with three different precursor architectures, bleogens pB1-15 from of the Cactaceae family. By combining proteomic and transcriptomic methods, we showed that the prototype, bleogen pB1, contained 36 amino acid residues, a six-cysteine motif typical of the six-cysteine-hevein-like peptide (6C-HLP) family, and a type I two-domain precursor consisting of an endoplasmic reticulum (ER) and a mature domain. In contrast, the precursors of the other 14 bleogens contained a type II three-domain architecture with a propeptide domain inserted between the ER and the mature bleogen domain. Four of these 14 bleogens display a third type of architecture with a tandemly repeating bleogen domain. A search of the Onekp database revealed that <1% plant species possess three different precursor architectures for the biosynthesis of 6C-HLPs, including , and sp. NMR analysis confirmed that bleogen pB1 has cystine-knot disulfide connectivity as well as a two-beta-sheet and a four-loop structural fold that is similar to other 6C-HLPs. Sequence analysis, structural studies, and modeling revealed that bleogen pB1 has a cation-polar-cation motif, a signature heparin-binding motif that was confirmed by heparin affinity chromatography. Cell-based assays showed that bleogen pB1 is non-toxic to mammalian cells but functions as an anti-Candida peptide. Taken together, our findings provide insight into the occurrence, functions and precursor architectures of CRPs in the cactus family.
富含半胱氨酸的肽（CRPs）在植物中发挥着重要的宿主防御作用。然而，关于仙人掌科植物中CRPs的信息有限，迄今为止仅描述了一种源自仙人掌的CRP。在此，我们报告了从仙人掌科植物中鉴定出15种具有三种不同前体结构的新型CRPs，即bleogens pB1 - 15。通过结合蛋白质组学和转录组学方法，我们发现原型bleogen pB1包含36个氨基酸残基，具有六半胱氨酸 - 橡胶素样肽（6C - HLP）家族典型的六半胱氨酸基序，以及由内质网（ER）和成熟结构域组成的I型双结构域前体。相比之下，其他14种bleogens的前体包含II型三结构域结构，在ER和成熟bleogen结构域之间插入了一个前肽结构域。这14种bleogens中的四种呈现出第三种结构类型，具有串联重复的bleogen结构域。对Onekp数据库的搜索显示，不到1%的植物物种具有用于6C - HLPs生物合成的三种不同前体结构，包括[具体植物名称1]、[具体植物名称2]和[具体植物名称3]。核磁共振分析证实，bleogen pB1具有胱氨酸结二硫键连接以及与其他6C - HLPs相似的双β - 折叠和四环结构折叠。序列分析、结构研究和[具体技术名称]建模表明，bleogen pB1具有阳离子 - 极性 - 阳离子基序，这是一种经肝素亲和色谱法证实的标志性肝素结合基序。基于细胞的试验表明，bleogen pB1对哺乳动物细胞无毒，但具有抗念珠菌肽的功能。综上所述，我们的研究结果为仙人掌科植物中CRPs的存在、功能和前体结构提供了深入了解。
