桔小实蝇肽聚糖识别蛋白基因BdPGRP-SB1的克隆及功能鉴定

【目的】为探究肽聚糖识别蛋白(PGRP)基因BdPGRP-SB1在桔小实蝇Bactrocera dorsalis免疫中的作用。【方法】本研究利用PCR克隆桔小实蝇BdPGRP-SB1全长cDNA序列;利用生物信息学软件对该基因核苷酸序列及其编码的氨基酸序列特征进行分析。采用RT-qPCR分析BdPGRP-SB1在桔小实蝇不同发育阶段(卵、幼虫、蛹、成虫)及5日龄成虫不同组织(中肠、马氏管、后肠、脂肪体、卵巢和精巢)中的表达模式;对桔小实蝇5日龄雌成虫分别注射大肠杆菌Escherichia coli 0111:B4肽聚糖(PGN-EB)和金黄色葡萄球菌Staphylococcus aureus肽聚糖(PGN-SA)后检测BdPGRP-SB1表达水平变化。利用RNAi沉默BdPGRP-SB1的表达,测定大肠杆菌和金黄色葡萄球菌诱导后桔小实蝇雌成虫的死亡率及大肠杆菌诱导后抗菌肽(AMP)基因attacin-A, defensin和diptercin表达变化情况。【结果】克隆获得桔小实蝇BdPGRP-SB1的全长cDNA序列(GenBank登录号: MN892482),开放阅读框长558 bp,编码185个氨基酸,其编码蛋白预测分子量为21.45 kD,等电点为8.57。序列分析表明,BdPGRP-SB1无跨膜结构域,具有PGRP保守结构域,前端具有信号肽,为分泌型蛋白;具有Zn²⁺依赖性酰胺酶活性和DAP型肽聚糖识别位点。系统进化分析发现,BdPGRP-SB1与辣椒实蝇B. latifrons的PGRP-SB1亲缘关系最近,氨基酸序列一致性达96%。发育表达模式表明,BdPGRP-SB1在桔小实蝇3日龄幼虫和成虫期高表达;组织表达谱结果显示BdPGRP-SB1在5日龄成虫各组织中均有表达,在脂肪体内表达量最高。PGN-EB和PGN-SA均能诱导桔小实蝇雌成虫体内BdPGRP-SB1表达水平变化。通过RNAi抑制BdPGRP-SB1表达后,注射大肠杆菌导致桔小实蝇雌成虫死亡率显著升高,以及attacin-A, defensin和diptercin表达量显著上调。【结论】结果说明桔小实蝇BdPGRP-SB1参与识别革兰氏阴性细菌,并可能参与桔小实蝇Imd途径调控其免疫反应。     

大鲵短型肽聚糖识别蛋白PGRP-S的克隆及其功能研究

实验构建了大鲵短型肽聚糖识别蛋白PGRP-S的真核表达质粒, 并对其功能进行了初步的研究。序列分析显示, 所克隆的大鲵PGRP-S的N端不含有信号肽; 其编码的氨基酸序列具有2个相距较近的半胱氨酸残基以及2个Zn2+结合位点。Western-blotting检测结果显示大鲵PGRP-S既可分泌到胞外, 也可滞留在胞内。体外抗菌实验的结果表明, 过表达大鲵PGRP-S能显著抑制迟缓爱德华氏菌(Edwardsiella tarda)在HEK293T细胞内和胞外培养基中的增殖。此外, 过表达大鲵PGRP-S能诱导NF-κB启动子的活性; 能结合Lys-type和Dap-type的肽聚糖但不能降解它们。研究结果表明大鲵PGRP-S在功能上类似于哺乳动物而有别于硬骨鱼类短型的肽聚糖识别蛋白。     

本期重点推介

正昆虫先天免疫主要依赖于模式识别受体(pattern recognition receptor,PRRs)通过识别入侵微生物表面的保守分子来区分异己。肽聚糖识别蛋白(peptidoglycan recognition protein,PGRP)是这类识别受体之一。抗菌肽是昆虫体液免疫中的重要组分,具有杀死病原体的作用。病原微生物侵染还可引发机体大量合成过氧化氢(H2O2)等活性氧分子。为探究家蝇Musca domestica肽聚糖识别蛋白PGRP-SC在应对     

鱼类肽聚糖识别蛋白的研究进展

肽聚糖识别蛋白(Peptidoglycan recognition proteins,PGRPs)是一类高度保守的模式识别受体(Pattern recognition receptors,PRRs)家族,能够识别细菌细胞壁的主要成分肽聚糖,进而激活并调节机体的先天性免疫反应。目前已报道的鱼类PGRP共23种,根据氨基酸序列的不同,PGRPs主要分为3类,分别是短型、中型和长型PGRPs。尽管鱼类PGRPs在大小、结构域布局及亚细胞定位方面有一定差异,但其C端的PGRP结构域是高度保守的。鱼类PGRPs在不同组织中广泛表达,在不同细菌的刺激下,鱼类PGRPs在各免疫组织的表达量均明显改变,推测鱼类PGRPs参与了机体的免疫应答过程。此外,鱼类PGRPs在生理过程、胚胎发育的先天性免疫调节中也扮演了重要角色。目前有关鱼类PGRPs的功能研究主要集中在病原识别能力,酰胺酶活性、杀菌抑菌性和免疫调节机制四个方面,尽管已经取得了一定的进展,然而对其作用机制的研究还不够深入,未来需要进一步深入的研究。针对鱼类PGRPs的结构、表达及功能进行综述,旨在为今后深入研究鱼类PGRPs的功能及应用提供思路。     

肽聚糖的生理功能及其在疾病诊断中的作用进展

肽聚糖(peptidoglycan, PGN)是细菌细胞壁的主要结构,与体内多种受体信号分子如核苷酸结合寡聚化结构域蛋白1/2(nucleotide-binding oligomerization domain protein 1/2, NOD1/2)、Toll样受体2(toll like receptor 2, TLR2)和PGN识别蛋白(peptidoglycan recognition proteins, PGRP)等结合后,参与人体如发烧、睡眠和骨生成等生理功能。研究发现,PGN作为病原微生物细菌的结构成分,在临床血流感染和自身免疫疾病诊断中也发挥着重要作用。现就PGN在人体内的代谢、功能及疾病诊断应用价值作一概述。     

光滑鳖甲肽聚糖识别蛋白的生物信息学分析

[目的]预测光滑鳖甲肽聚糖识别蛋白的结构与功能。[方法]采用生物信息学方法对该基因及其编码蛋白的基本理化性质、疏水性、信号肽、二级结构和亚细胞定位等方面进行预测和分析,同时构建其编码产物的系统进化树。[结果]此蛋白的理论分子量为21.882 k D,包含一个由20个氨基酸组成的信号肽,属亲水蛋白,分泌到胞外发挥作用,可能具有信号转导和响应胁迫与免疫反应的功能,与赤拟谷盗的同源性最高,具有能够与肽聚糖结合的保守的PGRP结构域和一个Ⅱ型酰胺酶结构域。[结论]光滑鳖甲肽聚糖识别蛋白Ap PGRP-FD1基因克隆成功,生物信息学分析及结合蛋白质结构与功能预测可为深入研究ApPGRP-FD1提供理论指导。     

小菜蛾PGRP-SA的体外表达及介导酚氧化酶活力的研究

肽聚糖识别蛋白(Peptidoglycan Recognition Proteins,PGRPs)是可以识别肽聚糖和含肽聚糖的细菌的一类模式识别受体,在介导酚氧化酶级联反应中起着重要的作用。本研究以实验室克隆的小菜蛾Px PGRP-SA(Gen Bank No.EU399240)为基础,RT-PCR克隆了其开放阅读框(ORF),在原核细胞中获得了高效重组表达,利用GST一步纯化的融合蛋白免疫新西兰大白兔,制备了抗血清,滴定效价为1∶51200。Western blot检测表明Micrococcus luteus和Serratia marcescens可以显著提高Px PGRP-SA在小菜蛾血淋巴中的含量。为了检测Px PGRP-SA与酚氧化酶PO的活力关系,本研究将Px PGRP-SA连接到真核表达载体p MT/Bip/V5/His A构建真核表达质粒p MTAPGRP,转染果蝇S2细胞中,获得稳定的细胞系,硫酸铜诱导获得表达后用anti-V5纯化获得重组蛋白Px PGRP-SA。将重组蛋白Px PGRP-SA与M.luteus和S.marcescens分别温育后,可以显著提高小菜蛾血浆中PO的活力。本研究结果阐明了重组蛋白Px PGRP-SA在小菜蛾体PO级联反应中的功能,为进一步研究Px PGRP-SA在小菜蛾体内免疫信号通路中的功能奠定了基础。     

小菜蛾整合素integrin β1基因的克隆及其功能分析

整合素(Integrin)是一种由α和β亚基组成的跨膜异二聚体蛋白,在昆虫血细胞对外物的包囊过程中起着重要的作用。为阐明integrinβ1参与小菜蛾Plutella xylostella体内细胞免疫中的功能,本研究利用RT-PCR结合RACE技术克隆了小菜蛾integrinβ1基因的cDNA全长序列,命名为PxIntβ1(Gen Bank登录号GQ178290)。小菜蛾PxIntβ1的cDNA全长序列为2 832 bp,开放阅读框为2 487 bp,编码828个氨基酸,成熟的氨基酸序列中有一个跨膜区和一个integrin亚基。系统进化树显示小菜蛾PxIntβ1与亚洲玉米螟Ostrinia furnacalis整合素的同源性最高,两者同源性达到78%。利用半定量RT-PCR技术检测PxIntβ1基因在小菜蛾不同发育历期(卵、1-4龄幼虫、蛹、成虫)、不同组织(血细胞、体壁、脂肪体、中肠、马氏管)和细菌(金黄色葡萄球菌和大肠杆菌混合菌液)诱导下的表达模式。半定量结果表明小菜蛾PxIntβ1基因在小菜蛾整个发育历期除了卵之外都有表达,4龄幼虫转录水平最高,在血细胞中特异性的高表达,混合细菌诱导2-48 h后,PxIntβ1基因在小菜蛾诱导后24 h达到诱导表达高峰。为了进一步获得重组蛋白PxIntβ1,本研究构建了原核表达质粒pET-32a-PxIntβ1,融合蛋白在大肠杆菌Eschericha coli BL21中获得高效表达,Ni-NTA一步纯化了融合蛋白,并免疫新西兰大白兔,获得了多克隆抗体anti-PxIntβ1。SDS-PAGE电泳和Western blot分析结果表明,His抗体和多克隆抗体anti-PxIntβ1能特异性识别融合蛋白PxIntβ1;进一步利用显微镜观察了小菜蛾血细胞对凝胶珠Sephadex-A25的包囊情况,结果表明抗血清anti-PxIntβ1处理过的小菜蛾血细胞对Sephadex-A25凝胶珠的包囊作用受到明显抑制,重组蛋白PxIntβ1可以提高小菜蛾血细胞对Sephadex-A25凝胶珠的包囊作用;以上研究结果表明小菜蛾PxIntβ1在小菜蛾细胞免疫中起着重要的作用。     

短短芽孢杆菌GZDF3中PilZ结构域基因的挖掘和糖基转移酶的原核表达

【背景】PilZ结构域是最早发现的环二鸟苷酸(Cyclic diguanylate,c-di-GMP)受体信号分子,与c-di-GMP结合后可以调控目标基因或者蛋白的活性,在细菌的生长过程中发挥着至关重要的作用,而短短芽孢杆菌中PilZ结构域的研究相对缺乏。【目的】挖掘短短芽孢杆菌GZDF3菌株中的PilZ结构域蛋白基因,并进行重组表达,为研究其功能奠定基础。【方法】从Pfam数据库中下载PilZ结构域模型,HMMScan软件扫描GZDF3全基因组序列,在保守结构域数据库(Conserved domain database,CDD)中分析蛋白保守结构域,Protein BLAST比对分析;采用ExPASy在线软件预测蛋白的基本理化性质;构建重组表达载体进行蛋白重组表达。【结果】GZDF3基因中存在5个含有PilZ结构域的蛋白编码基因,其中命名为Gene4836的基因经Protein BLAST比对分析显示其编码糖基转移酶,Gene1423为YcgR超家族蛋白编码基因,Gene1723编码透明质酸合成酶,属于糖基转移酶超家族2,其余Gene2571、Gene2956编码假定蛋白;Gene4836的编码产物分子量为24.08 kD,等电点为6.39,为酸性亲水性蛋白;C端有一个PilZ结构域;0.5 mmol/L乳糖诱导、30°C培养20 h,表达出一大小约为25kD的重组蛋白,与生物信息学预测结果相符。【结论】首次对短短芽孢杆菌含有PilZ结构域蛋白编码基因进行原核表达,并成功纯化出重组蛋白,为后续研究其功能奠定了基础。     

家蝇溶菌酶MDLZM2基因的克隆、序列分析及原核表达

对家蝇溶菌酶(Musca domestica lysozyme,MDLZM2)基因进行克隆、序列分析,构建原核表达载体并在大肠杆菌中表达。从Gen Bank家蝇基因组中筛选获得MDLZM2基因。以该基因的序列设计引物,进行PCR扩增,测序分析获得该基因完整编码序列。运用生物信息学方法对该基因及其编码蛋白的基本理化性质、信号肽、二级结构、三级结构和保守结构域等方面进行预测和分析。构建p EASY-E1-MDLZM2重组质粒,转化到大肠杆菌BL21(DE3)p Lys S Chemically Competent Cell中进行诱导表达及纯化。结果表明MDLZM2基因ORF全长552 bp,编码183个氨基酸,理论分子量21.2 k Da;等电点为6.13,具有Lysozyme家族的蛋白保守结构域。成功构建重组原核表达p EASY-E1-MDLZM2并诱导表达、纯化重组蛋白,为进一步研究该蛋白的生物学及免疫学活性奠定了基础。     

Peptidoglycan recognition proteins: a novel family of four human innate immunity pattern recognition molecules.

The innate immune system recognizes microorganisms through a series of pattern recognition receptors that are highly conserved in evolution. Insects have a family of 12 peptidoglycan recognition proteins (PGRPs) that recognize peptidoglycan, a ubiquitous component of bacterial cell walls. We report cloning of three novel human PGRPs (PGRP-L, PGRP-Ialpha, and PGRP-Ibeta) that together with the previously cloned PGRP-S, define a new family of human pattern recognition molecules. PGRP-L, PGRP-Ialpha, and PGRP-Ibeta have 576, 341, and 373 amino acids coded by five, seven, and eight exons on chromosomes 19 and 1, and they all have two predicted transmembrane domains. All mammalian and insect PGRPs have at least three highly conserved C-terminal PGRP domains located either in the extracellular or in the cytoplasmic (or in both) portions of the molecules. PGRP-L is expressed in liver, PGRP-Ialpha and PGRP-Ibeta in esophagus (and to a lesser extent in tonsils and thymus), and PGRP-S in bone marrow (and to a lesser extent in neutrophils and fetal liver). All four human PGRPs bind peptidoglycan and Gram-positive bacteria. Thus, these PGRPs may play a role in recognition of bacteria in these organs.     

INVOLVEMENT OF PEPTIDOGLYCAN RECOGNITION PROTEIN L6 IN ACTIVATION OF IMMUNE DEFICIENCY PATHWAY IN THE IMMUNE RESPONSIVE SILKWORM CELLS

The immune deficiency (Imd) signaling pathway is activated by Gram‐negative bacteria for producing antimicrobial peptides (AMPs). In Drosophila melanogaster, the activation of this pathway is initiated by the recognition of Gram‐negative bacteria by peptidoglycan (PGN) recognition proteins (PGRPs), PGRP‐LC and PGRP‐LE. In this study, we found that the Imd pathway is involved in enhancing the promoter activity of AMP gene in response to Gram‐negative bacteria or diaminopimelic (DAP) type PGNs derived from Gram‐negative bacteria in an immune responsive silkworm cell line, Bm‐NIAS‐aff3. Using gene knockdown experiments, we further demonstrated that silkworm PGRP L6 (BmPGRP‐L6) is involved in the activation of E. coli or E. coli‐PGN mediated AMP promoter activation. Domain analysis revealed that BmPGRP‐L6 contained a conserved PGRP domain, transmembrane domain, and RIP homotypic interaction motif like motif but lacked signal peptide sequences. BmPGRP‐L6 overexpression enhances AMP promoter activity through the Imd pathway. BmPGRP‐L6 binds to DAP‐type PGNs, although it also binds to lysine‐type PGNs that activate another immune signal pathway, the Toll pathway in Drosophila. These results indicate that BmPGRP‐L6 is a key PGRP for activating the Imd pathway in immune responsive silkworm cells.     

A peptidoglycan recognition protein from Sciaenops ocellatus is a zinc amidase and a bactericide with a substrate range limited to Gram-positive bacteria

Peptidoglycan recognition proteins (PGRPs) are a family of innate immune molecules that recognize bacterial peptidoglycan. PGRPs are highly conserved in invertebrates and vertebrates including fish. However, the biological function of teleost PGRP remains largely uninvestigated. In this study, we identified a PGRP homologue, SoPGLYRP-2, from red drum (Sciaenops ocellatus) and analyzed its activity and potential function. The deduced amino acid sequence of SoPGLYRP-2 is composed of 482 residues and shares 46-94% overall identities with known fish PGRPs. SoPGLYRP-2 contains at the C-terminus a single zinc amidase domain with conserved residues that form the catalytic site. Quantitative RT-PCR analysis detected SoPGLYRP-2 expression in multiple tissues, with the highest expression occurring in liver and the lowest expression occurring in brain. Experimental bacterial infection upregulated SoPGLYRP-2 expression in kidney, spleen, and liver in time-dependent manners. To examine the biological activity of SoPGLYRP-2, purified recombinant proteins representing the intact SoPGLYRP-2 (rSoPGLYRP-2) and the amidase domain (rSoPGLYRP-AD) were prepared from Escherichia coli. Subsequent analysis showed that rSoPGLYRP-2 and rSoPGLYRP-AD (i) exhibited comparable Zn²⁺-dependent peptidoglycan-lytic activity and were able to recognize and bind to live bacterial cells, (ii) possessed bactericidal effect against Gram-positive bacteria and slight bacteriostatic effect against Gram-negative bacteria, (iii) were able to block bacterial infection into host cells. These results indicate that SoPGLYRP-2 is a zinc-dependent amidase and a bactericide that targets preferentially at Gram-positive bacteria, and that SoPGLYRP-2 is likely to play a role in host innate immune defense during bacterial infection.     

Peptidoglycan recognition protein expression in mouse Peyer's Patch follicle associated epithelium suggests functional specialization

Mammalian Peyer's Patches possess specialized epithelium, the follicle associated epithelium (FAE), and specialized cells called M cells which mediate transcytosis of antigens to underlying lymphoid tissue. To identify FAE specific genes, we used TOGA gene expression profiling of microdissected mouse Peyer's Patch tissue. We found expression of laminin beta3 across the FAE, and scattered expression of peptidoglycan recognition protein (PGRP)-S. Using the M cell specific lectin Ulex europaeus agglutinin 1 (UEA-1), PGRP-S expression was nearly exclusively co-localized with UEA-1+ M cells. By contrast, the related gene PGRP-L was expressed among a subset of UEA-1 negative FAE cells. Expression of these proteins in transfected cells demonstrated distinct subcellular localization. PGRP-S showed a vesicular pattern and extracellular secretion, while PGRP-L showed localization to both the cytoplasm and the cell surface. The potential function of these PGRP proteins as pattern recognition receptors and their distinctive cellular distribution suggests a complex coordination among specialized cells of the FAE in triggering mucosal immunity and innate immune responses.     

The differentially spliced mouse tagL gene,homolog of tag7/PGRP gene family in mammals and Drosophila,can recognize Gram-positive and Gram-negative bacterial cell wall independently of T phage lysozyme homology domain

Tag7/PGRP, a recently characterized antimicrobial protein, is conserved from insects to mammals. Recently its involvement in Toll signalling in Drosophila was demonstrated. A number of genes representing a new family homologous to PGRP were identified in Drosophila and human. Here we describe a splicing pattern of the tagL gene, mouse member of tag7/PGRP family. Some of the identified splice variants lacked characteristics for the family T phage lysozyme homology domain (also known as PGRP domain). Accordingly to the predicted transmembrane domains, mouse TagL may be secreted as inducible proteins or retained on intracellular membranes. All detected splice variant isoforms of TagL bound Gram-positive, Gram-negative bacteria and peptidoglycan. This binding did not depend on the presence of T phage lysozyme homology domain but was associated with the C-terminal portion of the polypeptides. Thus, this variety of isoforms of a single gene may play a role in circulating bacteria recognition in mammals.     

Human peptidoglycan recognition protein-L is an N-acetylmuramoyl-L-alanine amidase

Peptidoglycan recognition proteins (PGRPs) are pattern recognition molecules coded by up to 13 genes in insects and 4 genes in mammals. In insects PGRPs activate antimicrobial pathways in the hemolymph and cells, or are peptidoglycan (PGN)-lytic amidases. In mammals one PGRP is an antibacterial neutrophil protein. We report that human PGRP-L is a Zn2+-dependent N-acetylmuramoyl-l-alanine amidase (EC 3.5.1.28), an enzyme that hydrolyzes the amide bond between MurNAc and l-Ala of bacterial PGN. The minimum PGN fragment hydrolyzed by PGRP-L is MurNAc-tripeptide. PGRP-L has no direct bacteriolytic activity. The other members of the human PGRP family, PGRP-Ialpha, PGRP-Ibeta, and PGRP-S, do not have the amidase activity. The C-terminal region of PGRP-L, homologous to bacteriophage and bacterial amidases, is required and sufficient for the amidase activity of PGRP-L, although its activity (in the N-terminal delta1-343 deletion mutant) is reduced. The Zn2+ binding amino acids (conserved in PGRP-L and T7 amidase) and Cys-419 (not conserved in T7 amidase) are required for the amidase activity of PGRP-L, whereas three other amino acids, needed for the activity of T7 amidase, are not required for the activity of PGRP-L. These amino acids, although required, are not sufficient for the amidase activity, because changing them to the "active" configuration does not convert PGRP-S into an active amidase. In conclusion, human PGRP-L is an N-acetylmuramoyl-l-alanine amidase and this function is conserved in prokaryotes, insects, and mammals.     

Bovine peptidoglycan recognition protein-S: antimicrobial activity, localization, secretion, and binding properties

Peptidoglycan (PGN) recognition proteins (PGRPs) are pattern recognition molecules of innate immunity that are conserved from insects to humans. Various PGRPs are reported to have diverse functions: they bind bacterial molecules, digest PGN, and are essential to the Toll pathway in Drosophila. One family member, bovine PGN recognition protein-S (bPGRP-S), has been found to bind and kill microorganisms in a PGN-independent manner, raising questions about the identity of the bPGRP-S ligand. Addressing this, we have determined the binding and microbicidal properties of bPGRP-S in a range of solutions approximating physiologic conditions. In this study we show that bPGRP-S interacts with other bacterial components, including LPS and lipoteichoic acid, with higher affinities than for PCP, as determined by their abilities to inhibit bPGRP-S-mediated killing of bacteria. Where and how PGRPs act in vivo is not yet clear. Using Immunogold electron microscopy, PGRP-S was localized to the dense/large granules of naive neutrophils, which contain the oxygen-independent bactericidal proteins of these cells, and to the neutrophil phagolysosome. In addition, Immunogold staining and secretion studies demonstrate that neutrophils secrete PGRP-S when exposed to bacteria. Bovine PGRP-S can mediate direct lysis of heat-killed bacteria; however, PGRP-S-mediated killing of bacteria is independent of this activity. Evidence that bPGRP-S has multiple activities and affinity to several bacterial molecules challenges the assumption that the PGRP family of proteins recapitulates the evolution of TLRs. Mammalian PGRPs do not have a single antimicrobial activity against a narrow range of target organisms; rather, they are generalists in their affinity and activity.     

Molecular cloning and characterization of peptidoglycan recognition proteins from the rockfish,Sebastes schlegeli

Peptidoglycan recognition proteins (PGRPs) are innate immune molecules that are structurally conserved through evolution in both invertebrate and vertebrate animals. Here we report the identification and characterization of two long forms of PGRP (SsPGRP-L1 and SsPGRP-L2) from the rockfish, Sebastes schlegeli. The deduced amino acid sequences of SsPGRP-L1 and SsPGRP-L2, 466 and 482 residues respectively, contain the conserved PGRP domain and the four Zn²⁺-binding amino acid residues required for amidase activity. In addition to peptidoglycan-lytic amidase activity, recombinant SsPGRPs have broad-spectrum antimicrobial activity like zebrafish PGRPs. RT-PCR analysis of total RNA shows that the expression patterns of SsPGRP-L1 and SsPGRP-L2 genes are different, though they are widely expressed in the tissues that come in contact with bacteria. Overall, these data suggest that rockfish PGRPs are involved in the innate host defense of S. schlegeli against bacterial infections.