DNA aptamers selectively target Leishmania infantum H2A protein

Green-synthesized chitosan‑carbon dot nanocomposite as turn-on aptasensor for detection and quantification of Leishmania infantum parasite

Leishmania is one of the most common diseases between human and animals, caused by Leishmania infantum parasite. Here, we have developed an ultra-selective turn-on fluorescent probe based on an aptamer and Chitosan-CD nanocomposite. The CD used in this study were synthesized using Quercus cap extract and a microwave-assisted approach. The Chitosan-CD nanocomposite was optimized using several microscopic and spectroscopic techniques to possess a bright fluorescence emission before adding aptamer and totally quenched fluorescence after addition of aptamer. The designed probe was proficient in the detection and quantification Leishmania infantum parasite by selective targeting of poly(A) binding protein (PABP) on the surface of the parasite. The designed fluorescent biosensor with high sensitivity, excellent selectivity, and a limit of detection (LOD) of 94 cells/mL of the Leishmania infantum parasite as well as a linear response in the ranges of 188-750 cells/mL and 3000-6000 cells/mL (R2 ≥ 0.98 for both linear ranges). Additionally, the selectivity of the designed probe was evaluated in the presence of different pathogenic species such as Trypanosoma brucei parasite and Staphylococcus aureus bacteria, as well as LiIF2α and LiP2a and BSA proteins as interference substances. The results of this study shows that using Chitosan-CD nanocomposite is a great strategy for developing selective turn-on probes with extraordinary accuracy and sensitivity in identifying Leishmania infantum parasite, especially in the early stages of the disease, and it is promising for the future clinical applications.

Neglected Zoonotic Diseases: Advances in the Development of Cell-Penetrating and Antimicrobial Peptides against Leishmaniosis and Chagas Disease

In 2020, the WHO established the road map for neglected tropical diseases 2021-2030, which aims to control and eradicate 20 diseases, including leishmaniosis and Chagas disease. In addition, since 2015, the WHO has been developing a Global Action Plan on Antimicrobial Resistance. In this context, the achievement of innovative strategies as an alternative to replace conventional therapies is a first-order socio-sanitary priority, especially regarding endemic zoonoses in poor regions, such as those caused by Trypanosoma cruzi and Leishmania spp. infections. In this scenario, it is worth highlighting a group of natural peptide molecules (AMPs and CPPs) that are promising strategies for improving therapeutic efficacy against these neglected zoonoses, as they avoid the development of toxicity and resistance of conventional treatments. This review presents the novelties of these peptide molecules and their ability to cross a whole system of cell membranes as well as stimulate host immune defenses or even serve as vectors of molecules. The efforts of the biotechnological sector will make it possible to overcome the limitations of antimicrobial peptides through encapsulation and functionalization methods to obtain approval for these treatments to be used in clinical programs for the eradication of leishmaniosis and Chagas disease.

Toward waterborne protozoa detection using sensing technologies

Drought and limited sufficient water resources will be the main challenges for humankind during the coming years. The lack of water resources for washing, bathing, and drinking increases the use of contaminated water and the risk of waterborne diseases. A considerable number of waterborne outbreaks are due to protozoan parasites that may remain active/alive in harsh environmental conditions. Therefore, a regular monitoring program of water resources using sensitive techniques is needed to decrease the risk of waterborne outbreaks. Wellorganized point-of-care (POC) systems with enough sensitivity and specificity is the holy grail of research for monitoring platforms. In this review, we comprehensively gathered and discussed rapid, selective, and easy-to-use biosensor and nanobiosensor technologies, developed for the early detection of common waterborne protozoa.

Aptamer-Based Technologies for Parasite Detection

Centuries of scientific breakthroughs have brought us closer to understanding and managing the spread of parasitic diseases. Despite ongoing technological advancements in the detection, treatment, and control of parasitic illnesses, their effects on animal and human health remain a major concern worldwide. Aptamers are single-stranded oligonucleotides whose unique three-dimensional structures enable them to interact with high specificity and affinity to a wide range of targets. In recent decades, aptamers have emerged as attractive alternatives to antibodies as therapeutic and diagnostic agents. Due to their superior stability, reusability, and modifiability, aptamers have proven to be effective bioreceptors for the detection of toxins, contaminants, biomarkers, whole cells, pathogens, and others. As such, they have been integrated into a variety of electrochemical, fluorescence, and optical biosensors to effectively detect whole parasites and their proteins. This review offers a summary of the various types of parasite-specific aptamer-based biosensors, their general mechanisms and their performance.

Enzyme-Linked Oligonucleotide Assay (ELONA)

Aptamers are single-stranded oligonucleotides able to recognize a target with high affinity and specificity. Aptamers are used in different diagnostics applications, highlighting, among all, variations of the traditional enzyme-linked immunosorbent assay (ELISA). In this chapter, we show the procedures for the development of two types of indirect ELONA: a sandwich ELONA and a direct ELONA coupled to either real-time quantitative PCR as a direct and sensitive readout.

Highly sensitive protein detection by aptamer-based single-molecule kinetic fingerprinting

Sensitive assays of protein biomarkers play critical roles in clinical diagnostics and biomedical research. Such assays typically employ immunoreagents such as monoclonal antibodies that suffer from several drawbacks, including relatively tedious production, significant batch-to-batch variability, and challenges in site-specific, stoichiometric modification with fluorophores or other labels. One proposed alternative to such immunoreagents, nucleic acid aptamers generated by systematic evolution of ligand by exponential enrichment (SELEX), can be chemically synthesized with much greater ease, precision, and reproducibility than antibodies. However, most aptamers exhibit relatively poor affinity, yielding low sensitivity in the assays employing them. Recently, single molecule recognition through equilibrium Poisson sampling (SiMREPS) has emerged as a platform for detecting proteins and other biomarkers with high sensitivity without requiring high-affinity detection probes. In this manuscript, we demonstrate the applicability and advantages of aptamers as detection probes in SiMREPS as applied to two clinically relevant biomarkers, VEGF₁₆₅ and IL-8, using a wash-free protocol with limits of detection in the low femtomolar range (3-9 fM). We show that the kinetics of existing RNA aptamers can be rationally optimized for use as SiMREPS detection probes by mutating a single nucleotide in the conserved binding region or by shortening the aptamer sequence. Finally, we demonstrate the detection of endogenous IL-8 from human serum at a concentration below the detection limit of commercial ELISAs.

Are Nanobiosensors an Improved Solution for Diagnosis of Leishmania?

Leishmaniasis is one of the deadliest neglected tropical diseases affecting 12–15 million people worldwide, especially in middle- and low-income countries. Rapid and accurate diagnosis of the disease is important for its adequate management and treatment. Several techniques are available for the diagnosis of leishmaniasis. Among these, parasitological and immunological tests are most widely used. However, in most cases, the utilized diagnostic techniques are not good enough, showing cross-reactivity and reduced accuracy. In recent years, many new methods have been reported with potential for improved diagnosis. This review focuses on the diagnosis of Leishmania exploring the biosensors and nanotechnology-based options for their detection. New developments including the use of nanomaterials as fluorophores, fluorescence quenchers as reducing agents and as dendrimers for signal improvement and amplification, together with the use of aptamers to replace antibodies are described. Future research opportunities to overcome the current limitations on the available diagnostic approaches are also discussed.

Aptamer-Based Western Blot for Selective Protein Recognition

Selective protein recognition is critical in molecular biology techniques such as Western blotting and ELISA. Successful detection of the target proteins in these methods relies on the specific interaction of the antibodies, which often bring a high production cost and require a long incubation time. Aptamers represent an alternative class of simple and affordable affinity reagents for protein recognition, and replacing antibodies with aptamers in Western blotting would potentially be more time- and cost-effective. In this work, multiple fluorescent DNA aptamers were isolated by in vitro selection to selectively label commonly used tag proteins including GST, MBP, and His-tag. The generated aptamers G1, M1, and H1 specifically bound to their cognate target proteins with nanomolar affinities, respectively. Compared with conventional antibody-based immunoblotting, such aptamer-based procedure gave a cleaner background and was able to selectively label target protein in a complex mixture. Lastly, the identified aptamers were also effective in recognition of different fusion proteins with the same tag, thus greatly expanding the scope of the potential applications of these aptamers. This work provided aptamers as useful molecular tools for selective protein recognition in Western blotting analysis.

Aptamers as a novel diagnostic and therapeutic tool and their potential use in parasitology

Los aptámeros son secuencias de ADN o ARN de cadena sencilla que adoptan la forma de estructuras tridimensionales únicas, lo cual les permite reconocer un blanco específico con gran afinidad. Sus usos potenciales abarcan, entre otros, el diagnóstico de enfermedades, el desarrollo de nuevos agentes terapéuticos, la detección de riesgos alimentarios, la producción de biosensores, la detección de toxinas, el transporte de fármacos en el organismo y la señalización de nanopartículas.

El pegaptanib es el único aptámero aprobado para uso comercial por la Food and Drug Administration (FDA). Otros aptámeros para el tratamiento de enfermedades están en la fase clínica de desarrollo.

En parasitología, se destacan los estudios que se vienen realizando en Leishmania spp., con la obtención de aptámeros que reconocen la proteína de unión a poliA (LiPABP) y que pueden tener potencial utilidad en la investigación, el diagnóstico y el tratamiento de la leishmaniasis. En cuanto a la malaria, se han obtenido aptámeros que permiten identificar eritrocitos infectados e inhiben la formación de rosetas, y otros que prometen ser alternativas para el diagnóstico al detectar de forma específica la proteína lactato deshidrogenasa (PfLDH). Para Cryptosporidium parvuum se han seleccionado aptámeros que detectan ooquistes a partir de alimentos o aguas contaminadas. Para Entamoeba histolytica se han aislado dos aptámeros llamados C4 y C5, que inhiben la proliferación in vitro de los trofozoítos y tienen potencial terapéutico. Los aptámeros contra Trypanosoma cruzi inhiben la invasión de células LLC-MK2 (de riñón de mono) en un 50 a 70 % y aquellos contra T. brucei transportan moléculas tóxicas al lisosoma parasitario como una novedosa estrategia terapéutica.

Los datos recopilados en esta revisión destacan los aptámeros como una alternativa para la investigación, el diagnóstico y el tratamiento contra parásitos de interés nacional.

DNA aptamers targeting Leishmania infantum H3 protein as potential diagnostic tools

Leishmaniasis is a disease caused by a parasite of the genus Leishmania that affects millions of people worldwide. These parasites are characterized by the presence of a DNA-containing granule, the kinetoplastid, located in the single mitochondrion at the base of the cell's flagellum. Interestingly, these flagellates do not condense chromatin during mitosis, possibly due to the specific molecular features of their histones. Although histones are extremely conserved proteins, kinetoplastid core histone sequences diverge significantly from those of higher eukaryotes. This divergence makes kinetoplastid core histones potential diagnostic and/or therapeutic targets. Aptamers are short single-stranded nucleic acids that are able to recognize target molecules with high affinity and specificity. Their binding capacity is a consequence of the particular three-dimensional structure acquired depending on their sequence. These molecules are currently used for detection, diagnosis and therapeutic purpose. Starting from a previously obtained ssDNA aptamer population against rLiH3 protein we have isolated two individual aptamers, AptLiH3#4 and AptLiH3#10. Next, we have performed ELONA, Western blot and slot blot assays to establish aptamer specificity and affinity for LiH3 histone. In addition, ELONA assays using peptides corresponding to overlapped sequences of LiH3 were made to map the aptamers:LiH3 interaction. Finally, different assays using aptamers were performed in order to evaluate the possibility of using these aptamers as sensing molecule to recognize the endogenous protein LiH3. Our results indicate that both aptamers have high affinity and specificity for the target and are able to detect the endogenous LiH3 histone protein in promastigotes lysates. In silico analysis reveals that these two aptamers have different potential secondary structure among them, however, both of them are able to recognize the same peptide sequences present in the protein. In conclusion, our findings indicate that these aptamers could be used for LiH3 histone detection and, in consequence, as potential biosensing molecules in a diagnostic tool for leishmaniasis.

Therapeutic applications of nucleic acid aptamers in microbial infections

Today, the treatment of bacterial infections is a major challenge, due to growing rate of multidrug-resistant bacteria, complication of treatment and increased healthcare costs. Moreover, new treatments for bacterial infections are limited. Oligonucleotide aptamers are single stranded DNAs or RNAs with target-selective high-affinity feature, which considered as nucleic acid-based affinity ligands, replacing monoclonal antibodies. The aptamer-based systems have been found to be talented tools in the treatment of microbial infections, regarding their promising anti-biofilm and antimicrobial activities; they can reduce or inhibit the effects of bacterial toxins, and inhibit pathogen invasion to immune cell, as well as they can be used in drug delivery systems. The focus of this review is on the therapeutic applications of aptamers in infections. In this regard, an introduction of infections and related challenges were presented, first. Then, aptamer definition and selection, with a brief history of aptamers development against various pathogens and toxins were reviewed. Diverse strategies of aptamer application in drug delivery, as well as, the effect of aptamers on the immune system, as the main natural agents of human defense against pathogens, were also discussed. Finally, the future trends in clinical applications of this technology were discussed.

Enzyme-Linked Aptamer Assay (ELAA) for Detection of Toxoplasma ROP18 Protein in Human Serum

Toxoplasma gondii engenders the common parasitic disease toxoplasmosis in almost all warm-blooded animals. Being a critical secretory protein, ROP18 is a major virulence factor of Toxoplasma. There are no reports about ROP18 detection in human serum samples with different clinical manifestations. New aptamers against ROP18 protein were developed through Systematic Evolution of Ligands by Exponential enrichment (SELEX). An Enzyme-Linked Aptamer Assay (ELAA) platform was developed using SELEX-derived aptamers, namely AP001 and AP002. The ELAA was used to evaluate total antigen from T. gondii RH strain (RH Ag) and recombinant protein of ROP18 (rROP18). The results showed that the ELAA presented higher affinity and specificity to RH Ag and rROP18, compared to negative controls. Detection limit of rROP18 protein in serum samples was measured by standard addition method, achieving a lower concentration of 1.56 μg/mL. Moreover, 62 seropositive samples with different clinical manifestations of toxoplasmosis and 20 seronegative samples were tested. A significant association between ELAA test positive for human serum samples and severe congenital toxoplasmosis was found (p = 0.006). Development and testing of aptamers-based assays opens a window for low-cost and rapid tests looking for biomarkers and improves our understanding about the role of ROP18 protein on the pathogenesis of human toxoplasmosis.

Advances on Aptamers against Protozoan Parasites

Aptamers are single-stranded DNA or RNA sequences with a unique three-dimensional structure that allows them to recognize a particular target with high affinity. Although their specific recognition activity could make them similar to monoclonal antibodies, their ability to bind to a large range of non-immunogenic targets greatly expands their potential as tools for diagnosis, therapeutic agents, detection of food risks, biosensors, detection of toxins, drug carriers, and nanoparticle markers, among others. One aptamer named Pegaptanib is currently used for treating macular degeneration associated with age, and many other aptamers are in different clinical stages of development of evaluation for various human diseases. In the area of parasitology, research on aptamers has been growing rapidly in the past few years. Here we describe the development of aptamers raised against the main protozoan parasites that affect hundreds of millions of people in underdeveloped and developing countries, remaining a major health concern worldwide, i.e. Trypanosoma spp., Plasmodium spp., Leishmania spp., Entamoeba histolytica, and Cryptosporidium parvuum. The latest progress made in this area confirmed that DNA and RNA aptamers represent attractive alternative molecules in the search for new tools to detect and treat these parasitic infections that affect human health worldwide.

Novel DNA Aptamers Against CCL21 Protein: Characterization and Biomedical Applications for Targeted Drug Delivery to T Cell-Rich Zones

The chemokine (C-C motif) ligand 21 (CCL21) is a cytokine that attracts CCR7-positive cells to the T cell (paracortical) zone of lymph nodes by directional migration of these cells along the CCL21 gradient. In this article, we sought to mimic this chemotactic mechanism, by identifying a novel aptamer that binds CCL21 with high affinity. In vitro selection of DNA aptamers was performed by the Systematic Evolution of Ligands by Exponential Enrichment. Quantitative polymerase chain reaction (qPCR) and enzyme-linked oligonucleotide assay were used to screen for high-affinity aptamers against human and mouse CCL21 protein, respectively. Three such aptamers were identified. Surface plasmon resonance showed equilibrium dissociation constant (K_d) for these three aptamers in the nano to picomolar range. Cytotoxicity assays showed <10% toxicity in HEK293 and HL-60 cells. Last, in vivo biodistribution was successfully performed and CCL21 chemokine-binding aptamers were quantified within the draining lymph nodes and spleen using qPCR. Fluorescence microscopy revealed that one of the aptamers showed significantly higher presence in the paracortex than the control aptamer. The use of anti-CCL21 aptamers to mimic the chemotaxis mechanism thus represents a promising approach to achieve targeted delivery of drugs to the T cell-rich zones of the lymph node. This may be important for the treatment of HIV infection and the eradication of HIV reservoirs.

Targeting the polyadenylation factor EhCFIm25 with RNA aptamers controls survival in Entamoeba histolytica

Messenger RNA 3'-end polyadenylation is an important regulator of gene expression in eukaryotic cells. In our search for new ways of treating parasitic infectious diseases, we looked at whether or not alterations in polyadenylation might control the survival of Entamoeba histolytica (the agent of amoebiasis in humans). We used molecular biology and computational tools to characterize the mRNA cleavage factor EhCFIm25, which is essential for polyadenylation in E. histolytica. By using a strategy based on the systematic evolution of ligands by exponential enrichment, we identified single-stranded RNA aptamers that target EhCFIm25. The results of RNA-protein binding assays showed that EhCFIm25 binds to the GUUG motif in vitro, which differs from the UGUA motif bound by the homologous human protein. Accordingly, docking experiments and molecular dynamic simulations confirmed that interaction with GUUG stabilizes EhCFIm25. Incubating E. histolytica trophozoites with selected aptamers inhibited parasite proliferation and rapidly led to cell death. Overall, our data indicate that targeting EhCFIm25 is an effective way of limiting the growth of E. histolytica in vitro. The present study is the first to have highlighted the potential value of RNA aptamers for controlling this human pathogen.

Application of aptamers in diagnostics, drug-delivery and imaging

Aptamers are small, single-stranded oligonucleotides (DNA or RNA) that bind to their target with high specificity and affinity. Although aptamers are analogous to antibodies for a wide range of target recognition and variety of applications, they have significant advantages over antibodies. Since aptamers have recently emerged as a class of biomolecules with an application in a wide array of fields, we need to summarize the latest developments herein. In this review we will discuss about the latest developments in using aptamers in diagnostics, drug delivery and imaging. We begin with diagnostics, discussing the application of aptamers for the detection of infective agents itself, antigens/ toxins (bacteria), biomarkers (cancer), or a combination. The ease of conjugation and labelling of aptamers makes them a potential tool for diagnostics. Also, due to the reduced off-target effects of aptamers, their use as a potential drug delivery tool is emerging rapidly. Hence, we discuss their use in targeted delivery in conjugation with siRNAs, nanoparticles, liposomes, drugs and antibodies. Finally, we discuss about the conjugation strategies applicable for RNA and DNA aptamers for imaging. Their stability and self-assembly after heating makes them superior over protein-based binding molecules in terms of labelling and conjugation strategies.

ABCs of DNA aptamer and related assay development

This review is intended to guide the novice in aptamer research and development to understand virtually all of the aptamer development options and currently available assay modalities. Aptamer development topics range from discussions of basic and advanced versions of Systematic Evolution of Ligands by EXponential Enrichment (SELEX) and SELEX variations involving incorporation of exotic unnatural nucleotides to expand library diversity for even greater aptamer affinity and specificity to improved next generation methods of DNA sequencing, screening and tracking aptamer development throughout the SELEX process and characterization of lead aptamer candidates. Aptamer assay development topics include descriptions of various colorimetric and fluorescent assays in microplates or on membranes including homogeneous beacon and multiplexed Fluorescence Resonance Energy Transfer (FRET) assays. Finally, a discussion of the potential for marketing successful aptamer-based assays or test kits is included.

Immuno Affinity SELEX for Simple, Rapid, and Cost-Effective Aptamer Enrichment and Identification against Aflatoxin B1

Aflatoxins are naturally occurring mycotoxins that contaminate food and agro commodities, leading to acute and chronic health conditions in human and animals. In the present work, an attempt was made to generate high-affinity single stranded DNA aptamers that specifically bind to Aflatoxin B1 (AFB1) by a modified Systemic Evolution of Ligands by Exponential Enrichment (SELEX) procedure with the aid of Immunoaffinity columns. Ten rounds of SELEX and alternating three counter SELEX rounds with a cocktail of related and other mycotoxins were performed to enhance the specificity. Resultant 105 aptamers were clustered into 12 groups according to their primary sequence homology. Candidates with lowest Gibbs free energy (dG value) and unique stem loop structures were selected for further characterization. Aptamers, AFLA5, AFLA53, and AFLA71 exhibiting lower K_d values (50.45 ± 11.06, 48.29 ± 9.45, and 85.02 ± 25.74 nM) were chosen for development of ELONA and determination of purification ability of toxin. The detection limit (LOD) of AFLA5 and AFLA71 was 20 and 40 ng/ml, respectively. HPLC analysis implied that selected aptamers were able to recover and quantify 82.2 to 96.21% (LOQ – 53.74 ng) and 78.3 to 94.22% (LOQ – 66.75 ng) of AFB1 from spiked corn samples, respectively. These findings indicate, immunoaffinity based SELEX can pave an alternative approach to screen aptamers against mycotoxin detection and purification.

Aptamers as a promising approach for the control of parasitic diseases

Aptamers are short single-stranded RNA or DNA oligonucleotides that are capable of binding various biological targets with high affinity and specificity. Their identification initially relies on a molecular process named SELEX (Systematic Evolution of Ligands by EXponential enrichment) that has been later modified in order to improve aptamer sensitivity, minimize duration and cost of the assay, as well as increase target types. Several biochemical modifications can help to enhance aptamer stability without affecting significantly target interaction. As a result, aptamers have generated a large interest as promising tools to compete with monoclonal antibodies for detection and inhibition of specific markers of human diseases. One aptamer-based drug is currently authorized and several others are being clinically evaluated. Despite advances in the knowledge of parasite biology and host–parasite interactions from “omics” data, protozoan parasites still affect millions of people around the world and there is an urgent need for drug target discovery and novel therapeutic concepts. In this context, aptamers represent promising tools for pathogen identification and control. Recent studies have reported the identification of “aptasensors” for parasite diagnosis, and “intramers” targeting intracellular proteins. Here we discuss various strategies that have been employed for intracellular expression of aptamers and expansion of their possible application, and propose that they may be suitable for the clinical use of aptamers in parasitic infections.

Use of aptamers in immunoassays

Aptamers, short single-chain DNA or RNA oligonucleotides, react specifically with small molecules, as well as with proteins. Unlike antibodies, they may be obtained relatively easily. Aptamers are now widely employed in immunological studies and could replace antibodies in immunoassays. In this short review, methods for immobilizing aptamers on various insoluble materials (so-called apta-sorbents) are described. Recent findings on their use in the detection and isolation of immunoglobulins and their application in various immunoassays are also discussed.

Modern affinity reagents: Recombinant antibodies and aptamers

Affinity reagents are essential tools in both basic and applied research; however, there is a growing concern about the reproducibility of animal-derived monoclonal antibodies. The need for higher quality affinity reagents has prompted the development of methods that provide scientific, economic, and time-saving advantages and do not require the use of animals. This review describes two types of affinity reagents, recombinant antibodies and aptamers, which are non-animal technologies that can replace the use of animal-derived monoclonal antibodies. Recombinant antibodies are protein-based reagents, while aptamers are nucleic-acid-based. In light of the scientific advantages of these technologies, this review also discusses ways to gain momentum in the use of modern affinity reagents, including an update to the 1999 National Academy of Sciences monoclonal antibody production report and federal incentives for recombinant antibody and aptamer efforts. In the long-term, these efforts have the potential to improve the overall quality and decrease the cost of scientific research.

Molecular and Functional Characterization of ssDNA Aptamers that Specifically Bind Leishmania infantum PABP

SUMMARY

A poly (A)-binding protein from Leishmania infantum (LiPABP) has been recently cloned and characterized in our laboratory. Although this protein shows a very high homology with PABPs from other eukaryotic organisms including mammals and other parasites, exist divergences along the sequence that convert them in potential diagnostic markers and/or therapeutics targets. Aptamers are oligonucleotide ligands that are selected in vitro by their affinity and specificity for the target as a consequence of the particular tertiary structure that they are able to acquire depending on their sequence. Development of high-affinity molecules with the ability to recognize specifically Leishmania proteins is essential for the progress of this kind of study.

RESULTS

We have selected a ssDNA aptamer population against a recombinant 6xHIS-LiPABP protein (rLiPABP) that is able to recognize the target with a low Kd. Cloning, sequencing and in silico analysis of the aptamers obtained from the population yielded three aptamers (ApPABP#3, ApPABP#7 and ApPABP#11) that significantly bound to PABP with higher affinity than the naïve population. These aptamers were analyzed by ELONA and slot blot to establish affinity and specificity for rLiPABP. Results demonstrated that the three aptamers have high affinity and specificity for the target and that they are able to detect an endogenous LiPABP (eLiPABP) protein amount corresponding to 2500 L. infantum promastigotes in a significant manner. The functional analysis of the aptamers also revealed that ApPABP#11 disrupts the binding of both Myc-LiPABP and eLiPABP to poly (A) in vitro. On the other hand, these aptamers are able to bind and purify LiPABP from complex mixes.

CONCLUSION

Results presented here demonstrate that aptamers represent new reagents for characterization of LiPABP and that they can affect LiPABP activity. At this respect, the use of these aptamers as therapeutic tool affecting the physiological role of PABP has to be analyzed.

Aptamers as a replacement for antibodies in enzyme-linked immunosorbent assay

The application of antibodies in enzyme-linked immunosorbent assay (ELISA) is the basis of this diagnostic technique which is designed to detect a potpourri of complex target molecules such as cell surface antigens, allergens, and food contaminants. However, development of the systematic evolution of Ligands by Exponential Enrichment (SELEX) method, which can generate a nucleic acid-based probe (aptamer) that possess numerous advantages compared to antibodies, offers the possibility of using aptamers as an alternative molecular recognition element in ELISA. Compared to antibodies, aptamers are smaller in size, can be easily modified, are cheaper to produce, and can be generated against a wide array of target molecules. The application of aptamers in ELISA gives rise to an ELISA-derived assay called enzyme-linked apta-sorbent assay (ELASA). As with the ELISA method, ELASA can be used in several different configurations, including direct, indirect, and sandwich assays. This review provides an overview of the strategies involved in aptamer-based ELASA.