Browsing by Author "Khati, Makobetsa"
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- ItemOpen AccessAn analysis of alcohol use and possible confounding risk factors for risky sexual behaviour amongst women in the rural Western Cape and urban Gauteng provinces(2013) Khati, Makobetsa; London, LeslieThe general aim of this thesis is therefore to analyse alcohol consumption variables and possible confounding risk factors associated with risky sexual behaviour amongst women in the urban city of Tshwane in Gauteng and the rural Western Cape sites, respectively.
- ItemOpen AccessThe development of aptamer-based probes for the detection of TB antigens ESAT-6.CFP-10 potential TB diagnostic tools(2013) Maserumule, Matsopiane Charlotte; Dheda, Keertan; Khati, Makobetsa; Gresh, LionelLack of point-of-care (PoC) diagnostic tools for TB hinders control of the disease, particularly in resource-limited, high HIV and TB prevalence countries. Therefore, there is a need for simple, rapid, accurate, and affordable PoC diagnostics to detect active TB early enough for opportune intervention. To develop TB detection probes that will constitute such diagnostics, our research group recently isolated DNA aptamers that bind to a putative marker for active TB; the ESAT-6.CFP-10 heterodimer. Aptamers are highly specific artificial mimics of antibodies that have shown great prospects in diagnostic applications. The aim of this study was to characterise the anti-ESAT-6.CFP-10 aptamers, and to optimise them into more specific and affordable detection probes for the development of potential PoC TB diagnostic tools.
- ItemOpen AccessHigh-throughput sequencing enhanced phage display identifies peptides that bind mycobacteria(Public Library of Science, 2013) Ngubane, Nqobile A C; Gresh, Lionel; Ioerger, Thomas R; Sacchettini, James C; Zhang, Yanjia J; Rubin, Eric J; Pym, Alexander; Khati, MakobetsaBacterial cell wall components have been previously used as infection biomarkers detectable by antibodies. However, it is possible that the surface of the Mycobacterium tuberculosis ( M. tb ), the causative agent of tuberculosis (TB), also possesses molecules which might be non-antigenic. This makes the probing of biomarkers on the surface of M. tb cell wall difficult using antibodies. Here we demonstrate the use of phage display technology to identify peptides that bind to mycobacteria. We identified these clones using both random clone picking and high throughput sequencing. We demonstrate that random clone picking does not necessarily identify highly enriched clones. We further showed that the clone displaying the CPLHARLPC peptide which was identified by Illumina sequencing as the most enriched, binds better to mycobacteria than three clones selected by random picking. Using surface plasmon resonance, we showed that chemically synthesised CPLHARLPC peptide binds to a 15 KDa peptide from M.tb H37Rv whole cell lysates. These observations demonstrate that phage display technology combined with high-throughput sequencing is a powerful tool to identify peptides that can be used for investigating potential non-antigenic biomarkers for TB and other bacterial infections.
- ItemOpen AccessHIV-1 subtype C unproductively infects human cardiomyocytes in vitro and induces apoptosis mitigated by an anti-gp120 aptamer(Public Library of Science, 2014) de Campos, Walter R Lopes; Chirwa, Nthato; London, Grace; Rotherham, Lia S; Morris, Lynn; Mayosi, Bongani M; Khati, MakobetsaHIV-associated cardiomyopathy (HIVCM) is of clinical concern in developing countries because of a high HIV-1 prevalence, especially subtype C, and limited access to highly active antiretroviral therapy (HAART). For these reasons, we investigated the direct and indirect effects of HIV-1 subtype C infection of cultured human cardiomyocytes and the mechanisms leading to cardiomyocytes damage; as well as a way to mitigate the damage. We evaluated a novel approach to mitigate HIVCM using a previously reported gp120 binding and HIV-1 neutralizing aptamer called UCLA1. We established a cell-based model of HIVCM by infecting human cardiomyocytes with cell-free HIV-1 or co-culturing human cardiomyocytes with HIV-infected monocyte derived macrophages (MDM). We discovered that HIV-1 subtype C unproductively (i.e. its life cycle is arrested after reverse transcription) infects cardiomyocytes. Furthermore, we found that HIV-1 initiates apoptosis of cardiomyocytes through caspase-9 activation, preferentially via the intrinsic or mitochondrial initiated pathway. CXCR4 receptor-using viruses were stronger inducers of apoptosis than CCR5 utilizing variants. Importantly, we discovered that HIV-1 induced apoptosis of cardiomyocytes was mitigated by UCLA1. However, UCLA1 had no protective effective on cardiomyocytes when apoptosis was triggered by HIV-infected MDM. When HIV-1 was treated with UCLA1 prior to infection of MDM, it failed to induce apoptosis of cardiomyocytes. These data suggest that HIV-1 causes a mitochondrial initiated apoptotic cascade, which signal through caspase-9, whereas HIV-1 infected MDM causes apoptosis predominantly via the death-receptor pathway, mediated by caspase-8. Furthermore the data suggest that UCLA1 protects cardiomyocytes from caspase-mediated apoptosis, directly by binding to HIV-1 and indirectly by preventing infection of MDM.
- ItemRestrictedA modeled structure of an aptamer-gp120 complex provides insight into the mechanism of HIV-1 neutralization(American Chemical Society, 2010) Joubert, Marisa K; Kinsley, Nichole; Capovilla, Alexio; Sewell, B Trevor; Jaffer, Mohamed A; Khati, MakobetsaThe HIV-1 envelope glycoprotein, gp120, is a key target for a class of drugs called entry inhibitors. Here we used molecular modeling to construct a three-dimensional model of an anti-gp120 RNA aptamer, B40t77, alone and in complex with gp120. An initial model of B40t77 was built from the predicted secondary structure and then subjected to a combination of energy minimization and molecular dynamics. To model the B40t77-gp120 complex, we docked the B40t77 predicted structure onto the CD4-induced epitope of the gp120 crystal structure. A series of gp120 point mutations in the predicted B40t77-gp120 interface were measured for their binding affinity for B40t77 by surface plasmon resonance. According to the model, of the 10 gp120 amino acids that showed a reduction in the level of binding when mutated to alanine, all of them are modeled as making direct contact with B40t77 as part of a hydrogen bonding network. Comparison by electron microscopy of the B40t77-gp120 complex with gp120 alone revealed that only the longest dimension of the complex significantly increased in length, in a manner consistent with the predicted model. Binding assays revealed that B40t77 can weaken the binding of gp120 to the monoclonal antibodies B6, B12, and 2G12, none of which have binding sites that overlap with B40t77, as well as strengthen the binding to the antibody 19b. Thus, B40t77 may induce distant conformational changes in gp120 that disrupt its association with host cells and may suggest a mechanism for aptamer neutralization of HIV-1.
- ItemOpen AccessSelection and application of ssDNA aptamers to detect active TB from sputum samples(Public Library of Science, 2012) Rotherham, Lia S; Maserumule, Charlotte; Dheda, Keertan; Theron, Jacques; Khati, MakobetsaBACKGROUND: Despite the enormous global burden of tuberculosis (TB), conventional approaches to diagnosis continue to rely on tests that have major drawbacks. The improvement of TB diagnostics relies, not only on good biomarkers, but also upon accurate detection methodologies. The 10-kDa culture filtrate protein (CFP-10) and the 6-kDa early secreted antigen target (ESAT-6) are potent T-cell antigens that are recognised by over 70% of TB patients. Aptamers, a novel sensitive and specific class of detection molecules, has hitherto, not been raised to these relatively TB-specific antigens. METHODS: DNA aptamers that bind to the CFP-10.ESAT-6 heterodimer were isolated. To assess their affinity and specificity to the heterodimer, aptamers were screened using an enzyme-linked oligonucleotide assay (ELONA). One suitable aptamer was evaluated by ELONA using sputum samples obtained from 20 TB patients and 48 control patients (those with latent TB infection, symptomatic non TB patients, and healthy laboratory volunteers). Culture positivity for Mycobacterium tuberculosis (Mtb) served as the reference standard. Accuracy and cut-points were evaluated using ROC curve analysis. RESULTS: Twenty-four out of the 66 aptamers that were isolated bound significantly (p<0.05) to the CFP-10.ESAT-6 heterodimer and six were further evaluated. Their dissociation constant (K D ) values were in the nanomolar range. One aptamer, designated CSIR 2.11, was evaluated using sputum samples. CSIR 2.11 had sensitivity and specificity of 100% and 68.75% using Youden's index and 35% and 95%, respectively, using a rule-in cut-point. CONCLUSION: This preliminary proof-of-concept study suggests that a diagnosis of active TB using anti-CFP-10.ESAT-6 aptamers applied to human sputum samples is feasible.