Rudd Sarah R, Miranda Leticia Silva, Curtis Hannah R, Bigot Yves, Diaz-Mendoza Mercedes, Hice Robert, Nizet Victor, Park Hyun-Woo, Blaha Gregor, Federici Brian A, Bideshi Dennis K
Program in Biomedical Sciences, Department of Biological Sciences, California Baptist University, Riverside, CA 92504, USA.
School of Medicine, Loma Linda University, Loma Linda, CA 92350, USA.
Biology (Basel). 2023 Nov 11;12(11):1421. doi: 10.3390/biology12111421.
The three most important commercial bacterial insecticides are all derived from subspecies of (). Specifically, subsp. (Btk) and subsp. (Bta) are used to control larval lepidopteran pests. The third, subsp. (Bti), is primarily used to control mosquito and blackfly larvae. All three subspecies produce a parasporal body (PB) during sporulation. The PB is composed of insecticidal proteins that damage the midgut epithelium, initiating a complex process that results in the death of the insect. Among these three subspecies of , Bti is unique as it produces the most complex PB consisting of three compartments. Each compartment is bound by a multilaminar fibrous matrix (MFM). Two compartments contain one protein each, Cry11Aa1 and Cyt1Aa1, while the third contains two, Cry4Aa1/Cry4Ba1. Each compartment is packaged independently before coalescing into the mature spherical PB held together by additional layers of the MFM. This distinctive packaging process is unparalleled among known bacterial organelles, although the underlying molecular biology is yet to be determined. Here, we present structural and molecular evidence that the MFM has a hexagonal pattern to which Bti proteins Bt152 and Bt075 bind. Bt152 binds to a defined spot on the MFM during the development of each compartment, yet its function remains unknown. Bt075 appears to be derived from a bacteriophage major capsid protein (MCP), and though its sequence has markedly diverged, it shares striking 3-D structural similarity to the phage HK97 Head 1 capsid protein. Both proteins are encoded on Bti's pBtoxis plasmid. Additionally, we have also identified a six-amino acid motif that appears to be part of a novel molecular process responsible for targeting the Cry and Cyt proteins to their cytoplasmic compartments. This paper describes several previously unknown features of the Bti organelle, representing a first step to understanding the biology of a unique process of sorting and packaging of proteins into PBs. The insights from this research suggest a potential for future applications in nanotechnology.
三种最重要的商业细菌杀虫剂均源自苏云金芽孢杆菌（）的亚种。具体而言，库斯塔克亚种（Btk）和鲇泽亚种（Bta）用于防治鳞翅目幼虫害虫。第三种，以色列亚种（Bti），主要用于防治蚊子和蚋的幼虫。这三个亚种在孢子形成过程中都会产生一个伴孢晶体（PB）。伴孢晶体由破坏中肠上皮的杀虫蛋白组成，引发一个复杂过程，导致昆虫死亡。在苏云金芽孢杆菌的这三个亚种中，Bti 独一无二，因为它产生的伴孢晶体最为复杂，由三个隔室组成。每个隔室都由多层纤维基质（MFM）包裹。两个隔室分别包含一种蛋白质，即 Cry11Aa1 和 Cyt1Aa1，而第三个隔室包含两种蛋白质，Cry4Aa1/Cry4Ba1。每个隔室在合并形成由 MFM 的额外层维系在一起的成熟球形伴孢晶体之前都是独立包装的。这种独特的包装过程在已知的细菌细胞器中是无与伦比的，尽管其潜在的分子生物学机制尚待确定。在此，我们提供了结构和分子证据，表明 MFM 具有一种六边形模式，Bti 蛋白 Bt152 和 Bt075 与之结合。在每个隔室发育过程中，Bt152 会结合到 MFM 上的一个特定位置，但其功能仍然未知。Bt075 似乎源自噬菌体主要衣壳蛋白（MCP），尽管其序列有明显差异，但它与噬菌体 HK97 头部 1 衣壳蛋白具有惊人的三维结构相似性。这两种蛋白都由 Bti 的 pBtoxis 质粒编码。此外，我们还鉴定出一个六氨基酸基序，它似乎是一个新的分子过程的一部分，该过程负责将 Cry 和 Cyt 蛋白靶向输送到它们的细胞质隔室。本文描述了 Bti 细胞器的几个此前未知的特征，这是理解将蛋白质分类和包装到伴孢晶体这一独特过程的生物学机制的第一步。这项研究的见解表明了其在纳米技术未来应用中的潜力。
