Chang M X, Nie P, Wei L L
State Key Laboratory of Freshwater Ecology and Biotechnology, and Laboratory of Fish Diseases, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province 430072, PR China.
Mol Immunol. 2007 Apr;44(11):3005-23. doi: 10.1016/j.molimm.2006.12.029. Epub 2007 Feb 12.
Peptidoglycan recognition protein (PGRP) specifically binds to peptidoglycan and is considered to be one of the pattern recognition proteins in the innate immunity of insect and mammals. Using a database mining approach and RT-PCR, multiple peptidoglycan recognition protein (PGRP) like genes have been discovered in fish including zebrafish Danio rerio, Japanese pufferfish TakiFugu rubripes and spotted green pufferfish Tetraodon nigroviridis. They share the common features of those PGRPs in arthropod and mammals, by containing a conserved PGRP domain. Based on the predicted structures, the identified zebrafish PGRP homologs resemble short and long PGRP members in arthropod and mammals. The identified PGRP genes in T. nigroviridis and TakiFugu rubripes resemble the long PGRPs, and the short PGRP genes have not been found in T. nigroviridis and TakiFugu rubripes databases. Computer modelling of these molecules revealed the presence of three alpha-helices and five or six beta-strands in all fish PGRPs reported in the present study. The long PGRP in teleost fish have multiple alternatively spliced forms, and some of the identified spliced variants, e.g., tnPGRP-L3 and tnPGRP-L4 (tn: Tetraodon nigroviridis), exhibited no characters present in the PGRP homologs domain. The coding regions of zfPGRP6 (zf: zebrafish), zfPGRP2-A, zfPGRP2-B and zfPGRP-L contain five exons and four introns; however, the other PGRP-like genes including zfPGRPSC1a, zfPGRPSC2, tnPGRP-L1-, tnPGRP-L2 and frPGRP-L (fr: Takifugu rubripes) contain four exons and three introns. In zebrafish, long and short PGRP genes identified are located in different chromosomes, and an unknown locus containing another long PGRP-like gene has also been found in zebrafish, demonstrating that multiple PGRP loci may be present in fish. In zebrafish, the constitutive expressions of zfPGRP-L, zfPGRP-6 and zfPGRP-SC during ontogeny from unfertilized eggs to larvae, in different organs of adult, and the inductive expression following stimulation by Flavobacterium columnare, were detected by real-time PCR, but the levels and patterns varied for different PGRP genes, implying that different short and long PGRPs may play different roles in innate immune response.
肽聚糖识别蛋白（PGRP）能特异性结合肽聚糖，被认为是昆虫和哺乳动物先天免疫中的模式识别蛋白之一。通过数据库挖掘方法和逆转录聚合酶链反应（RT-PCR），在鱼类中发现了多个类肽聚糖识别蛋白（PGRP）基因，包括斑马鱼（Danio rerio）、日本河豚（Takifugu rubripes）和黑点绿河豚（Tetraodon nigroviridis）。它们具有节肢动物和哺乳动物中PGRPs的共同特征，都含有一个保守的PGRP结构域。基于预测结构，已鉴定出的斑马鱼类PGRP同源物类似于节肢动物和哺乳动物中的短型和长型PGRP成员。在黑点绿河豚和日本河豚中鉴定出的PGRP基因类似于长型PGRPs，而在黑点绿河豚和日本河豚数据库中未发现短型PGRP基因。对这些分子的计算机建模显示，本研究报道的所有鱼类PGRPs中都存在三个α螺旋和五个或六个β链。硬骨鱼中的长型PGRP有多种可变剪接形式，一些已鉴定出的剪接变体，如tnPGRP-L3和tnPGRP-L4（tn：黑点绿河豚），在PGRP同源结构域中没有表现出相应特征。zfPGRP6（zf：斑马鱼）、zfPGRP2-A、zfPGRP2-B和zfPGRP-L的编码区包含五个外显子和四个内含子；然而，其他类PGRP基因，包括zfPGRPSC1a、zfPGRPSC2、tnPGRP-L1、tnPGRP-L2和frPGRP-L（fr：日本河豚）包含四个外显子和三个内含子。在斑马鱼中，已鉴定出的长型和短型PGRP基因位于不同染色体上，并且在斑马鱼中还发现了一个含有另一个长型类PGRP基因的未知基因座，这表明鱼类中可能存在多个PGRP基因座。在斑马鱼中，通过实时PCR检测了zfPGRP-L、zfPGRP-6和zfPGRP-SC在从未受精卵到幼虫的个体发育过程中、成体不同器官中的组成型表达，以及柱状黄杆菌刺激后的诱导表达，但不同PGRP基因的水平和模式有所不同，这意味着不同的短型和长型PGRPs可能在先天免疫反应中发挥不同作用。
