Identification of a novel class of annexin genes

Rapid Detection of Aspergillus fumigatus Using Multiple Cross Displacement Amplification Combined With Nanoparticles-Based Lateral Flow

Aspergillus fumigatus is an opportunistic, ubiquitous, saprophytic mold which can cause infection in the lungs, nose, eyes, brain, and bones in humans, especially in immunocompromised patients. However, it is difficult to diagnose A. fumigatus infection quickly. Here, we introduce a new detection method, namely multiple cross displacement amplification (MCDA) combined with nanoparticle-based lateral flow biosensor (LFB) (MCDA-LFB), which was proved to be fast, reliable, and simple for detecting A. fumigatus. We designed a set of 10 primers targeting the gene annexin ANXC4 of A. fumigatus. The best MCDA condition is 66 °C for 35 min. The minimum concentration that can be detected by this method was 10 fg. In the case of 100 sputum samples, 20 (20%) and 15 (15%) samples were positive by MCDA-LFB and PCR method, respectively. MCDA-LFB and traditional culture method showed the same results. Compared with the culture method, the diagnostic accuracy of MCDA-LFB can reach 100%. It showed that the MCDA-LFB method has better detection ability than the PCR method. We found that the whole process could be controlled within 60 min including the preparation of DNA (20 min), MCDA reaction (35 min) and results reporting (2 min). These results show that this assay is suitable for the rapid, sensitive and specific detection of A. fumigatus in clinical samples.

Simple and rapid detection Aspergillus fumigatus by loop-mediated isothermal amplification coupled with lateral flow biosensor assay

AIMS

We have developed a new diagnostic technique, termed loop-mediated isothermal amplification coupled with lateral flow biosensor (LAMP-LFB), which has been successfully applied to the detection of Aspergillus fumigatus.

MATERIAL AND METHODS

A set of six LAMP primers was designed according to the A. fumigatus-specific anxC4 gene, which specifically recognized eight different regions of the target sequence. The LFB was employed for reporting the A. fumigatus-LAMP results, and the visual readouts were obtained within 2 min. The strains of A. fumigatus species and non-A. fumigatus species were used to test the assay's sensitivity and examine the analytical specificity of the target assay. Optimal LAMP conditions were 66°C for 50 min. The limit of detection is 100 fg. No cross-reactions were obtained, and the specificity of LAMP-LFB assay was 100%. The whole process of the assay, including 20 min of DNA preparation, 50 min of constant temperature amplification, and 2 min of detection by the sensor strip, took a total of 72 min (less than 75 min). Among 89 sputum specimens for clinical evaluation, 10 (11·23%) samples were A. fumigatus-positive by LAMP-LFB and traditional culture method, 9 (10·11%) samples were A. fumigatus-positive by PCR method. Compared with culture method, the diagnostic accuracy of LAMP-LFB method was 100%.

CONCLUSIONS

The novel LAMP-LFB detection technology established in the current research is a rapid and reliable detection tool for A. fumigatus.

SIGNIFICANCE AND IMPACT OF THE STUDY

This novel LAMP-LFB assay can quickly, specifically and sensitively detect A. fumigatus, thereby speeding up the detection process and increasing the detection rate. In addition, it can also be used as a new molecular method for detection of A. fumigatus in clinical and laboratory areas.

The enigmatic role of fungal annexins: the case of Cryptococcus neoformans

Annexins are multifunctional proteins that bind to phospholipid membranes in a calcium-dependent manner. Annexins play a myriad of critical and well-characterized roles in mammals, ranging from membrane repair to vesicular secretion. The role of annexins in the kingdoms of bacteria, protozoa and fungi have been largely overlooked. The fact that there is no known homologue of annexins in the yeast model organism Saccharomyces cerevisiae may contribute to this gap in knowledge. However, annexins are found in most medically important fungal pathogens, with the notable exception of Candida albicans. In this study we evaluated the function of the one annexin gene in Cryptococcus neoformans, a causative agent of cryptococcosis. This gene CNAG_02415, is annotated in the C. neoformans genome as a target of calcineurin through its transcription factor Crz1, and we propose to update its name to cryptococcal annexin, AnnexinC1. C. neoformans strains deleted for AnnexinC1 revealed no difference in survival after exposure to various chemical stressors relative to wild-type strain, as well as no major alteration in virulence or mating. The only alteration observed in strains deleted for AnnexinC1 was a small increase in the titan cells' formation in vitro. The preservation of annexins in many different fungal species suggests an important function, and therefore the lack of a strong phenotype for annexin-deficient C. neoformans indicates either the presence of redundant genes that can compensate for the absence of AnnexinC1 function or novel functions not revealed by standard assays of cell function and pathogenicity.

Development and Evaluation of a Loop-Mediated Isothermal Amplification Method for Rapid Detection of Aspergillus fumigatus

Aspergillus fumigatusis a conditional pathogen and the major cause of life-threatening invasive aspergillosis (IA) in immunocompromised patients. The early and rapid detection ofA. fumigatusinfection is still a major challenge. In this study, the new member of the fungal annexin family, annexin C4, was chosen as the target to design a loop-mediated isothermal amplification (LAMP) assay for the rapid, specific, and sensitive detection ofA. fumigatus The evaluation of the specificity of the LAMP assay that was developed showed that no false-positive results were observed for the 22 non-A. fumigatusstrains, including 5 species of theAspergillusgenus. Its detection limit was approximately 10 copies per reaction in reference plasmids, with higher sensitivity than that of real-time quantitative PCR (qPCR) at 10(2)copies for the same target. Clinical samples from a total of 69 patients with probable IA (n =14) and possible IA (n= 55) were subjected to the LAMP assay, and positive results were found for the 14 patients with probable IA (100%) and 34 patients with possible IA (61.82%). When detection using the LAMP assay was compared with that using qPCR in the 69 clinical samples, the LAMP assay demonstrated a sensitivity of 89.19% and the concordance rate for the two methods was 72.46%. Accordingly, we report that a valuable LAMP assay for the rapid, specific, and simple detection ofA. fumigatusin clinical testing has been developed.

Fungal annexins: a mini review

The large family of annexins is composed of more than a thousand members which are typically phospholipid-binding proteins. Annexins act in a number of signalling networks and membrane trafficking events which are fundamental to cell physiology. Annexins exert their functions mainly through their calcium-dependent membrane binding abilities; however, some calcium-independent interactions have been documented in the literature. Although mammalian and plant annexins have been well characterized, little is known about this family in fungi. This mini review summarizes the available data on fungal annexins.

Annexin C4 in A. fumigatus: a proteomics approach to understand the function

Annexin C4 has been identified as a new member of fungal annexin family. In search of function, we have generated an annexin C4 disruptant strain of human pathogen, Aspergillus fumigatus. Detailed phenotypic analysis confirmed a non essential role of annexin C4 in the growth and sporulation of this pathogen. We applied a comparative proteomics strategy to understand the possible role of this protein in the fungus. The modification of respiratory chain proteins and stress response proteins suggests the occurrence of a mild oxidative stress in anxC4 disruptant strain. This may indicate a possible anti stress function of annexin C4 in A. fumigatus.

Role of insulin in Cr(VI)-mediated genotoxicity in Neurospora crassa

AIMS

Chromium (III) is an insulinomimetic agent whose biological and/or environmental availability is frequently in the form of Cr(VI), which is known to be toxic. Wall-less mutant of Neurospora crassa (FGSC stock no. 4761) is known to possess insulin receptor in its cell membrane and hence is a good model for Cr toxicity studies. This study explores the toxicity of Cr(VI) and the possible consequences on simultaneous exposure to insulin in N. crassa.

METHODS AND RESULTS

Comet assay of N. crassa cells treated with 100 μmol l⁻¹ Cr(VI) showed up to 50% reduction in comet tail lengths when incubated simultaneously with 0.4 U insulin. Fluorescence measurement in Cr(VI)-treated cells using DCFH-DA showed six- to eightfold increase in free radical generation, which was reduced to fourfold by 0.4 U insulin. Annexin-V/PI Flow cytometry analysis indicated necrotic cell death up to 28.7 ± 3.6% and 68.6 ± 2.5% on Cr(VI) exposure at concentrations 100 and 500 μmol l⁻¹ which was reduced by 68.3 ± 3.2% and 48.9 ± 3.6%, respectively, upon addition of insulin.

CONCLUSION

Insulin-mediated protection from DNA damage by Cr(VI) is because of scavenging of free radicals liberated during exposure to Cr(VI).

SIGNIFICANCE AND IMPACT OF THE STUDY

Overall, Cr(VI) toxicity depends upon available insulin, indicating that Cr(VI) toxicity may be a serious issue in insulin-deficient individuals with diabetes.

Annexins

Annexins are multifunctional lipid-binding proteins. Plant annexins are expressed throughout the life cycle and are under environmental control. Their association or insertion into membranes may be governed by a range of local conditions (Ca(2+), pH, voltage or lipid identity) and nonclassical sorting motifs. Protein functions include exocytosis, actin binding, peroxidase activity, callose synthase regulation and ion transport. As such, annexins appear capable of linking Ca(2+), redox and lipid signalling to coordinate development with responses to the biotic and abiotic environment. Significant advances in plant annexin research have been made in the past 2 yr. Here, we review the basis of annexin multifunctionality and suggest how these proteins may operate in the life and death of a plant cell.

Molecular characterization and anticoagulant activity of a novel annexin derived from the Taenia solium

A novel annexin gene was isolated from the Taenia solium cDNA library by degenerate PCR. The purified protein was generated by hydrolysis with thrombin in glutathione S-transferase (GST) affinity chromatography following expression in GST tagged pGEX-5T vector. It shares the common structural features of the annexin family and specially possesses two unique fragments between repeating domains II and III which do not exist in other annexin family members revealed by aligning and homology modeling, hence it was designated as Tso ANXB2 according to the new nomenclature of annexins. According to the parasitic behaviors of the origin, a series of coagulation assays was performed, indicating that Tso ANXB2 inhibits extrinsic blood coagulation pathway and platelet aggregation also has platelet binding activity. Nevertheless, the mutant protein deleting the consensus coagulation-related KGD motif of Tso ANXB2 showed significant decreasing platelet binding and anticoagulation activity.

Identification of the first Oomycete annexin as a (1→3)-β-d-glucan synthase activator

(1-->3)-beta-D-Glucans are major components of the cell walls of Oomycetes and as such they play an essential role in the morphogenesis and growth of these microorganisms. Despite the biological importance of (1-->3)-beta-D-glucans, their mechanisms of biosynthesis are poorly understood. Previous studies on (1-->3)-beta-D-glucan synthases from Saprolegnia monoica have shown that three protein bands of an apparent molecular weight of 34, 48 and 50 kDa co-purify with enzyme activity. However, none of the corresponding proteins have been identified. Here we have identified, purified, sequenced and characterized a protein from the 34 kDa band and clearly shown that it has all the biochemical properties of proteins from the annexin family. In addition, we have unequivocally demonstrated that the purified protein is an activator of (1-->3)-beta-D-glucan synthase. This represents a new type of function for proteins belonging to the annexin family. Two other proteins from the 48 and 50 kDa bands were identified as ATP synthase subunits, which most likely arise from contaminations by mitochondria during membrane preparation. The results, which are discussed in relation with the possible regulation mechanisms of (1-->3)-beta-D-glucan synthases, represent a first step towards a better understanding of cell wall polysaccharide biosynthesis in Oomycetes.

ADAMs are present in fungi: identification of two novel ADAM genes in Aspergillus fumigatus

The ADAMs are a family of integral membrane proteases involved in shedding and fusion events in animal tissues. Here, we report the identification of two ADAMs, ADM-A and ADM-B, in the pathogenic fungus Aspergillus fumigatus. The domain structure of metazoan ADAMs was seen in ADM-A and -B, although with some differences. ADAMs were identified in other filamentous fungi and phylogenetic analysis indicated that the fungal ADAMs were monophyletic and most closely related to metazoan ADAM 10 and 17. Recombinant ADM-B protease specifically cleaved casein and albumin while recombinant propeptide+protease was inactive. A sheddase function is therefore proposed for fungal ADAMs.

Genes and molecules involved in Aspergillus fumigatus virulence

Aspergillus fumigatus causes a wide range of diseases that include mycotoxicosis, allergic reactions and systemic diseases (invasive aspergillosis) with high mortality rates. Pathogenicity depends on immune status of patients and fungal strain. There is no unique essential virulence factor for development of this fungus in the patient and its virulence appears to be under polygenetic control. The group of molecules and genes associated with the virulence of this fungus includes many cell wall components, such as beta-(1-3)-glucan, galactomannan, galactomannanproteins (Afmp1 and Afmp2), and the chitin synthetases (Chs; chsE and chsG), as well as others. Some genes and molecules have been implicated in evasion from the immune response, such as the rodlets layer (rodA/hyp1 gene) and the conidial melanin-DHN (pksP/alb1 gene). The detoxifying systems for Reactive Oxygen Species (ROS) by catalases (Cat1p and Cat2p) and superoxide dismutases (MnSOD and Cu, ZnSOD), had also been pointed out as essential for virulence. In addition, this fungus produces toxins (14 kDa diffusible substance from conidia, fumigaclavin C, aurasperon C, gliotoxin, helvolic acid, fumagilin, Asp-hemolysin, and ribotoxin Asp fI/mitogilin F/restrictocin), allergens (Asp f1 to Asp f23), and enzymatic proteins as alkaline serin proteases (Alp and Alp2), metalloproteases (Mep), aspartic proteases (Pep and Pep2), dipeptidyl-peptidases (DppIV and DppV), phospholipase C and phospholipase B (Plb1 and Plb2). These toxic substances and enzymes seems to be additive and/or synergistic, decreasing the survival rates of the infected animals due to their direct action on cells or supporting microbial invasion during infection. Adaptation ability to different trophic situations is an essential attribute of most pathogens. To maintain its virulence attributes A. fumigatus requires iron obtaining by hydroxamate type siderophores (ornitin monooxigenase/SidA), phosphorous obtaining (fos1, fos2, and fos3), signal transductional falls that regulate morphogenesis and/or usage of nutrients as nitrogen (rasA, rasB, rhbA), mitogen activated kinases (sakA codified MAP-kinase), AMPc-Pka signal transductional route, as well as others. In addition, they seem to be essential in this field the amino acid biosynthesis (cpcA and homoaconitase/lysF), the activation and expression of some genes at 37 degrees C (Hsp1/Asp f12, cgrA), some molecules and genes that maintain cellular viability (smcA, Prp8, anexins), etc. Conversely, knowledge about relationship between pathogen and immune response of the host has been improved, opening new research possibilities. The involvement of non-professional cells (endothelial, and tracheal and alveolar epithelial cells) and professional cells (natural killer or NK, and dendritic cells) in infection has been also observed. Pathogen Associated Molecular Patterns (PAMP) and Patterns Recognizing Receptors (PRR; as Toll like receptors TLR-2 and TLR-4) could influence inflammatory response and dominant cytokine profile, and consequently Th response to infec tion. Superficial components of fungus and host cell surface receptors driving these phenomena are still unknown, although some molecules already associated with its virulence could also be involved. Sequencing of A. fumigatus genome and study of gene expression during their infective process by using DNA microarray and biochips, promises to improve the knowledge of virulence of this fungus.

Evolutionary perspective on annexin calcium-binding domains

Molecular systematic analysis of the annexin gene superfamily characterized the evolutionary origin, frequency and range of structural variation in calcium interaction domains that are considered intrinsic for membrane targeting and ion channel function. Approximately 36% of annexin repeat domains in an estimated 100 distinct subfamilies contained amino acid changes consistent with the functional loss of type two calcium-binding sites. At least 11% of annexin domains contained a novel K/H/RGD motif conserved in particular subfamilies and manifest in all phyla, apparently via convergent evolution. The first yeast annexin from Yarrowia lipolytica was classified in the ANXC1 subfamily with fungal and mycetozoan representatives. This clade had intact calcium-binding sites but disruption of the normally well-conserved, mid-repeat 4 region implicated in calcium channel regulation. Conversely, a tandem pair of novel annexins from the amphioxus Branchiostoma floridae resembled annexin A13 in gene structure and conserved the charged amino acids associated with the internal hydrophilic pore, but were devoid of external type 2 calcium-binding sites and incorporated K/RGD motifs instead, like annexin A9. The selective erosion of calcium-binding sites in annexin domains and the occurrence of alternate ligands in the same exposed, interhelical loops are pervasive features of the superfamily. This suggests greater complexity than previously appreciated in the mechanisms controlling annexin membrane interaction and calcium channel operation.

TheAspergillus nigerannexin,anxC3.1is constitutively expressed and is not essential for protein secretion

An annexin, anxC3.1, was isolated and characterised from the industrially important filamentous fungus Aspergillus niger. anxC3.1 is a single copy gene encoding a 506 amino acid predicted protein which contains four annexin repeats. Disruption of the anxC3.1 gene did not lead to any visible changes in phenotype, nor in the levels of secreted protein, nor specifically in glucoamylase production, suggesting no major role in secretion. anxC3.1 expression was found to be unaltered under a variety of conditions such as increased secretion, altered nitrogen source, heat shock, and decreased Ca2+ levels, indicating that anxC3.1 is constitutively expressed. This is the first reported functional characterisation of a fungal annexin.