Unexpected homology between inducible cell wall protein QID74 of filamentous fungi and BR3 salivary protein of the insect Chironomus

Abstract

A gene, qid74, of mycoparasitic filamentous fungus Trichoderma harzianum and its allies encodes a cell wall protein that is induced by replacing glucose in the culture medium with chitin (simulated mycoparasitism conditions). Because no trace of this gene can be detected in related species such as Gibberella fujikuroi and Saccharomyces cerevisiae, the qid74 gene appears to have arisen de novo within the genus Trichoderma. Qid74 protein, 687 residues long, is now seen as highly conserved tandem repeats of the 59-residue-long unit. This unit itself, however, may have arisen as tandem repeats of the shorter 13-residue-long basic unit. Within the genus Trichoderma, the amino acid sequence of Qid74 proteins has been conserved in toto. The most striking is the fact that Qid74 shares 25.3% sequence identity with the carboxyl-terminal half of the 1,572-residue-long BR3 protein of the dipteran insect Chironomus tentans. BR3 protein is secreted by the salivary gland of each aquatic larva of Chironomus to form a tube to house itself. Furthermore, the consensus sequence derived from these 59-residue-long repeating units resembles those of epidermal growth factor-like domains found in divergent invertebrate and vertebrate proteins as to the positions of critical cysteine residues and homology of residues surrounding these cysteines.

The Cryptosporidium Oocyst Wall Protein Is a Member of a Multigene Family and Has a Homolog in Toxoplasma

“…It is possible that the proteins have similar roles, and it is therefore of interest to study the localization and function of the mosquito proteins. A similar convergence of structure and possible function might also underlie the cysteine periodicity in cell wall protein QID74 of filamentous fungi (gi:3250920) (11), the BR3 salivary protein of the dipteran insect Chironomus (gi:7058) (11), and the multigene family of surface antigenic proteins in Paramecium (gi:3250920) (17). Many proteins have a cysteine periodicity deriving from domain repetition, such as the extensive tandem arrays of the six-cysteine epidermal growth factor-like domain found in proteins with widespread phylogenetic distribution, including numerous proteins encoded by the Caenorhabditis elegans genome and several proteins encoded by the Plasmodium genome.…”

The qid74 gene from Trichoderma harzianum has a role in root architecture and plant biofertilization

“…The T. harzianum qid74 gene encodes a cysteine-rich cell wall protein with an unexpected homology to a salivary protein of the dipteran insect Chironomus (Rey et al, 1998). This gene is induced in cultures simulating mycoparasitism conditions by inclusion of 2 % chitin or 0.1 % fungal cell walls (Rosado et al, 2007).…”

“…The deduced 704 aa sequence of QID74 (Rey et al, 1998) has 14 repetitions, of which eight are 59 aa in length and have the typical eight cysteine residues found in hydrophobins that could explain the role of this protein in cell wall protection and hydrophobic adhesion. However, QID74 is a high-molecular-mass protein and its amino acid sequence repetitions do not fit into the typical consensus patterns between the first and eighth cysteine residues found in hydrophobins.…”

“…A number of fungal genes were identified to be overexpressed within the first hours of contact with the host. Among the significantly upregulated Trichoderma genes in the interaction with tomato plants in the absence of phytopathogenic fungi we identified the qid74 gene, encoding a cell wall protein with cysteine-rich repetitive regions with tri-(CXC) and penta-peptidic (CXXXC) motifs previously shown to be induced in Trichoderma by chitin (Rey et al, 1998). This finding was of particular interest since qid74 had been previously related to mycoparasitic processes in this strain (Rosado et al, 2007), but so far it had not been related to Trichoderma-plant interactions.…”

Evolutionary Origins of a Bioactive Peptide Buried within Preproalbumin

“…Although a few long, seemingly convergent protein sequences have been documented (Lawn et al, 1997;Rey et al, 1998;Robson et al, 2000), motifs that are reported to have converged upon similar protein sequence and 3D structure are short and only moderately conserved in sequence. The best known examples of such similar motifs in different protein folds contain three to four conserved residues, often interspersed with one or two nonconserved residues (Lupas et al, 2001).…”