Key Laboratory for Insect-Pollinator Biology of the Ministry of Agriculture and Rural Affairs, Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Beijing 100093, China.
College of Biological Science and Engineering, Fuzhou University, Fuzhou, Fujian 350108, China.
Int J Mol Sci. 2020 Apr 1;21(7):2441. doi: 10.3390/ijms21072441.
Peptidoglycan recognition proteins (PGRPs) play an important role in the defense against invading microbes via the recognition of the immunogenic substance peptidoglycan (PGN). Bees possess fewer PGRPs than and but retain two important immune pathways, the Toll pathway and the Imd pathway, which can be triggered by the recognition of Dap-type PGN by PGRP-LCx with the assistance of PGRP-LCa in . There are three isoforms of PGRP-LC including PGRP-LCx, PGRP-LCa and PGRP-LCy in . Our previous study showed that a single PGRP-LC exists in bumblebees. In this present study, we prove that the bumblebee PGRP-LC (Bl-PGRP-LC) can respond to an infection with Gram-negative bacterium through binding to the Dap-type PGNs directly, and that infection induces the quick and strong upregulation of , and . Moreover, the Bl-PGRP-LC exhibits a very strong affinity for the Dap-type PGN, much stronger than the affinity exhibited by the PGRP-LC from the more eusocial honeybee (Am-PGRP-LC). In addition, mutagenesis experiments showed that the residue His is the anchor residue for the binding to the Dap-type PGN and forms a hydrogen bond with MurNAc rather than meso-Dap, which interacts with the anchor residue Arg of PGRP-LCx in . Therefore, bumblebee PGRP-LC possesses exclusive characteristics for the immune response among insect PGRPs.
肽聚糖识别蛋白（PGRPs）通过识别免疫原性物质肽聚糖（PGN）在抵御入侵微生物中发挥重要作用。与 和 相比，蜜蜂拥有较少的 PGRPs，但保留了两条重要的免疫途径，即 Toll 途径和 Imd 途径，这两条途径可以通过 PGRP-LCx 识别 Dap 型 PGN 并在 的协助下被激活。 在 中存在三种 PGRP-LC 同工型，包括 PGRP-LCx、PGRP-LCa 和 PGRP-LCy。我们之前的研究表明，单一的 PGRP-LC 存在于大黄蜂中。在本研究中，我们证明了大黄蜂 PGRP-LC（Bl-PGRP-LC）可以通过直接结合 Dap 型 PGN 来应对革兰氏阴性菌 的感染，并且 感染诱导 、 和 的快速和强烈上调。此外，Bl-PGRP-LC 对 Dap 型 PGN 表现出非常强的亲和力，比来自更社会性的蜜蜂 （Am-PGRP-LC）的 PGRP-LC 强得多。此外，突变实验表明，残基 His 是与 Dap 型 PGN 结合的锚定残基，并与 MurNAc 形成氢键，而不是与锚定残基 Arg 相互作用的 meso-Dap，Arg 与 PGRP-LCx 在 中相互作用。因此，大黄蜂 PGRP-LC 在昆虫 PGRPs 中具有独特的免疫反应特征。
