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Hirsutellin A: A Paradigmatic Example of the Insecticidal Function of Fungal Ribotoxins.

Herrero-Galán E, García-Ortega L, Olombrada M, Lacadena J, Del Pozo ÁM, Gavilanes JG, Oñaderra M - Insects (2013)

Bottom Line: Thus, the consideration of hirsutellin A, an insecticidal protein, as a singular ribotoxin recalled the idea of the biological activity of these toxins as insecticidal agents.Further studies have demonstrated that the most representative member of the ribotoxin family, α-sarcin, also shows strong toxic action against insect cells.The aim of this review is to serve as a compilation of the facts that allow identification of HtA as a paradigmatic example of the insecticidal function of fungal ribotoxins.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Bioquímica y Biología Molecular I, Universidad Complutense, 28040 Madrid, Spain. eherrero@cnb.csic.es.

ABSTRACT
The fungal pathogen Hirsutella thompsonii produces an insecticidal protein named hirsutellin A (HtA), which has been described to be toxic to several species of mites, insect larvae, and cells. On the other hand, on the basis of an extensive biochemical and structural characterization, HtA has been considered to be a member of the ribotoxins family. Ribotoxins are fungal extracellular ribonucleases, which inactivate ribosomes by specifically cleaving a single phosphodiester bond located at the large rRNA. Although ribotoxins were brought to light in the 1960s as antitumor agents, their biological function has remained elusive. Thus, the consideration of hirsutellin A, an insecticidal protein, as a singular ribotoxin recalled the idea of the biological activity of these toxins as insecticidal agents. Further studies have demonstrated that the most representative member of the ribotoxin family, α-sarcin, also shows strong toxic action against insect cells. The determination of high resolution structures, the characterization of a large number of mutants, and the toxicity assays against different cell lines have been the tools used for the study of the mechanism of action of ribotoxins at the molecular level. The aim of this review is to serve as a compilation of the facts that allow identification of HtA as a paradigmatic example of the insecticidal function of fungal ribotoxins.

No MeSH data available.


Related in: MedlinePlus

Phylogenetic analysis [42] for the most important members of the Barnase superfamily. Numbers shown in the phylogram are distances corresponding to the amino acid sequence alignment of Figure 1.
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insects-04-00339-f002: Phylogenetic analysis [42] for the most important members of the Barnase superfamily. Numbers shown in the phylogram are distances corresponding to the amino acid sequence alignment of Figure 1.

Mentions: Ribotoxins are considered to be naturally engineered proteins that evolved from nontoxic ribonucleases [10]. They exhibit a high degree of identity (above 60%), including two disulphide bridges conserved along the whole family (Figure 1) [9,37,39,40]. Interestingly, HtA shares this characteristic, although it is 20 residues shorter than the other ribotoxins and shows only 25% sequence identity with previously known members of the family [37]. These were the reasons why HtA appeared initially after its discovery as a feasible candidate to be an evolutionary intermediate between T1-like RNases and ribotoxins (Figure 2). However, the further characterization of HtA showed that it maintains all the ribotoxin abilities, proving that these can be accommodated into a shorter amino acid sequence [30,41]. Thus, it has been suggested that HtA could actually be a refined ribotoxin that would have evolved further in order to become smaller and more economical.


Hirsutellin A: A Paradigmatic Example of the Insecticidal Function of Fungal Ribotoxins.

Herrero-Galán E, García-Ortega L, Olombrada M, Lacadena J, Del Pozo ÁM, Gavilanes JG, Oñaderra M - Insects (2013)

Phylogenetic analysis [42] for the most important members of the Barnase superfamily. Numbers shown in the phylogram are distances corresponding to the amino acid sequence alignment of Figure 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4553468&req=5

insects-04-00339-f002: Phylogenetic analysis [42] for the most important members of the Barnase superfamily. Numbers shown in the phylogram are distances corresponding to the amino acid sequence alignment of Figure 1.
Mentions: Ribotoxins are considered to be naturally engineered proteins that evolved from nontoxic ribonucleases [10]. They exhibit a high degree of identity (above 60%), including two disulphide bridges conserved along the whole family (Figure 1) [9,37,39,40]. Interestingly, HtA shares this characteristic, although it is 20 residues shorter than the other ribotoxins and shows only 25% sequence identity with previously known members of the family [37]. These were the reasons why HtA appeared initially after its discovery as a feasible candidate to be an evolutionary intermediate between T1-like RNases and ribotoxins (Figure 2). However, the further characterization of HtA showed that it maintains all the ribotoxin abilities, proving that these can be accommodated into a shorter amino acid sequence [30,41]. Thus, it has been suggested that HtA could actually be a refined ribotoxin that would have evolved further in order to become smaller and more economical.

Bottom Line: Thus, the consideration of hirsutellin A, an insecticidal protein, as a singular ribotoxin recalled the idea of the biological activity of these toxins as insecticidal agents.Further studies have demonstrated that the most representative member of the ribotoxin family, α-sarcin, also shows strong toxic action against insect cells.The aim of this review is to serve as a compilation of the facts that allow identification of HtA as a paradigmatic example of the insecticidal function of fungal ribotoxins.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Bioquímica y Biología Molecular I, Universidad Complutense, 28040 Madrid, Spain. eherrero@cnb.csic.es.

ABSTRACT
The fungal pathogen Hirsutella thompsonii produces an insecticidal protein named hirsutellin A (HtA), which has been described to be toxic to several species of mites, insect larvae, and cells. On the other hand, on the basis of an extensive biochemical and structural characterization, HtA has been considered to be a member of the ribotoxins family. Ribotoxins are fungal extracellular ribonucleases, which inactivate ribosomes by specifically cleaving a single phosphodiester bond located at the large rRNA. Although ribotoxins were brought to light in the 1960s as antitumor agents, their biological function has remained elusive. Thus, the consideration of hirsutellin A, an insecticidal protein, as a singular ribotoxin recalled the idea of the biological activity of these toxins as insecticidal agents. Further studies have demonstrated that the most representative member of the ribotoxin family, α-sarcin, also shows strong toxic action against insect cells. The determination of high resolution structures, the characterization of a large number of mutants, and the toxicity assays against different cell lines have been the tools used for the study of the mechanism of action of ribotoxins at the molecular level. The aim of this review is to serve as a compilation of the facts that allow identification of HtA as a paradigmatic example of the insecticidal function of fungal ribotoxins.

No MeSH data available.


Related in: MedlinePlus