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LEC-2, a highly variable lectin in the lichen Peltigera membranacea.

ABSTRACT: Lectins are a diverse group of carbohydrate binding proteins often involved in cellular interactions. A lectin gene, lec-2, was identified in the mycobiont of the lichen Peltigera membranacea. Sequencing of lec-2 open reading frames from 21 individual samples showed an unexpectedly high level of polymorphism in the deduced protein (LEC-2), which was sorted into nine haplotypes based on amino acid sequence. Calculations showed that the rates of nonsynonymous versus synonymous nucleotide substitutions deviated significantly from the null hypothesis of neutrality, indicating strong positive selection. Molecular modeling revealed that most amino acid replacements were around the putative carbohydrate-binding pocket, indicating changes in ligand binding. Lectins have been thought to be involved in the recognition of photobiont partners in lichen symbioses, and the hypothesis that positive selection of LEC-2 is driven by variation in the Nostoc photobiont partner was tested by comparing mycobiont LEC-2 haplotypes and photobiont genotypes, as represented by the rbcLX region. It was not possible to pair up the two types of marker sequences without conflicts, suggesting that positive selection of LEC-2 was not due to variation in photobiont partners.

SUBMITTER: Manoharan SS

PROVIDER: S-EPMC3589653 | biostudies-literature | 2012 Dec

REPOSITORIES: biostudies-literature

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LEC-2, a highly variable lectin in the lichen Peltigera membranacea.

Manoharan Sheeba S SS Miao Vivian P W VP Andrésson Olafur S OS

Symbiosis (Philadelphia, Pa.) 20121215 1-3

Lectins are a diverse group of carbohydrate binding proteins often involved in cellular interactions. A lectin gene, lec-2, was identified in the mycobiont of the lichen Peltigera membranacea. Sequencing of lec-2 open reading frames from 21 individual samples showed an unexpectedly high level of polymorphism in the deduced protein (LEC-2), which was sorted into nine haplotypes based on amino acid sequence. Calculations showed that the rates of nonsynonymous ver ...[more]

PMID: 23482294

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Project description:Microbes are commonly studied as individual species, but they exist as mixed assemblages in nature. At present, we know very little about the spatial organization of the molecules, including natural products that are produced within these microbial networks. Lichens represent a particularly specialized type of symbiotic microbial assemblage in which the component microorganisms exist together. These composite microbial assemblages are typically comprised of several types of microorganisms representing phylogenetically diverse life forms, including fungi, photosymbionts, bacteria, and other microbes. Here, we employed matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) imaging mass spectrometry to characterize the distributions of small molecules within a Peltigera lichen. In order to probe how small molecules are organized and localized within the microbial consortium, analytes were annotated and assigned to their respective producer microorganisms using mass spectrometry-based molecular networking and metagenome sequencing. The spatial analysis of the molecules not only reveals an ordered layering of molecules within the lichen but also supports the compartmentalization of unique functions attributed to various layers. These functions include chemical defense (e.g., antibiotics), light-harvesting functions associated with the cyanobacterial outer layer (e.g., chlorophyll), energy transfer (e.g., sugars) surrounding the sun-exposed cyanobacterial layer, and carbohydrates that may serve a structural or storage function and are observed with higher intensities in the non-sun-exposed areas (e.g., complex carbohydrates). IMPORTANCE Microbial communities have evolved over centuries to live symbiotically. The direct visualization of such communities at the chemical and functional level presents a challenge. Overcoming this challenge may allow one to visualize the spatial distributions of specific molecules involved in symbiosis and to define their functional roles in shaping the community structure. In this study, we examined the diversity of microbial genes and taxa and the presence of biosynthetic gene clusters by metagenomic sequencing and the compartmentalization of organic chemical components within a lichen using mass spectrometry. This approach allowed the identification of chemically distinct sections within this composite organism. Using our multipronged approach, various fungal natural products, not previously reported from lichens, were identified and two different fungal layers were visualized at the chemical level.

Project description:As an important pattern-recognition receptor (PRR), C-type lectins (CTLs) play significant roles in recognizing microbes and battle against pathogenic microorganism in innate immunity. In this study, two tandem threonine containing CTLs (designated as EcThr-LecA and EcThr-LecB) were identified from Exopalaemon carinicauda. The full-length cDNA of EcThr-LecA and EcThr-LecB consisted of 1521 and 1518 bp with 1251 and 1242 bp open reading frame encoding a protein with 412 and 413 amino acids, respectively. The genome structure of EcThr-LecA included 10 exons and 9 introns, and the sequences of intron6 and intron7 were variable. The nucleotide sequence of intron2 in EcThr-LecB was specific and different with that of EcThr-LecA. EcThr-LecA and EcThr-LecB proteins were predicted to have a signal peptide, two conserved carbohydrate recognition domain (CRD), and tandem threonine region. The expression levels of EcThr-LecA and EcThr-LecB in the intestine were significantly up-regulated after Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenge. RNA interference (RNAi) was used to explore the effects of EcThr-LecB silencing on the mRNA expression of anti-lipopolysaccharide factor (ALF), crustin (CRU), and lysozyme (LYSO). Knock down of EcThr-LecB could evidently down-regulate the expression of eight different antibacterial peptides (AMPs), including EcALF2, EcCRU1, EcCRU3, EcCRU4, EcLYSO1, EcLYSO2, EcLYSO3, and EcLYSO4, whereas make no effect on the transcription of EcALF1, EcALF3, EcCRU2, and EcLYSO5. The recombinant two CRD domains and tandem threonine region (RLecB) of EcThr-LecB could bind diverse bacteria, lipopolysaccharide, and peptidoglycans in vitro. In addition, RLecB could accelerate the clearance of V. parahaemolyticus in vivo. The present data indicated that new-found tandem threonine containing CTLs in E. carinicauda may act as PRR to participate in the innate immune defense against pathogens by the recognition of non-self, regulation of AMPs, and clearance of invaders.

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LEC-2, a highly variable lectin in the lichen Peltigera membranacea.

Publications

LEC-2, a highly variable lectin in the lichen <i>Peltigera membranacea.</i>

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