Browsing by Author "Christoffels, Alan"

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    The development of computational biology in South Africa : successes achieved and lessons learnt
    (PLoS, 2016) Mulder, Nicola J.; Christoffels, Alan; De Oliveira, Tulio; Gamieldien, Junaid; Hazelhurst, Scott; Joubert, Fourie; Kumuthini, Judit; Pillay, Che S.; Snoep, Jacky L.; Bishop, Ozlem Tastan; Tiffin, Nicki
    Bioinformatics is now a critical skill in many research and commercial environments as biological data are increasing in both size and complexity. South African researchers recognized this need in the mid-1990s and responded by working with the government as well as international bodies to develop initiatives to build bioinformatics capacity in the country. Significant injections of support from these bodies provided a springboard for the establishment of computational biology units at multiple universities throughout the country, which took on teaching, basic research and support roles. Several challenges were encountered, for example with unreliability of funding, lack of skills, and lack of infrastructure. However, the bioinformatics community worked together to overcome these, and South Africa is now arguably the leading country in bioinformatics on the African continent. Here we discuss how the discipline developed in the country, highlighting the challenges, successes, and lessons learnt.
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    Exome sequencing combined with semantic discovery identifies strong disease-associated candidates in a single case of relapsing remitting multiple sclerosis
    (BioMed Central, 2012-10) Jalali Sefid Dashti; Kotze, Maritha; Janse Van Rensburg, Susan; Christoffels, Alan; Gamieldien, Junaid
    As known disease-associated variants identified through large cohort-based studies often explain only a small percentage of genetic risk in multifactorial disorders such as multiple sclerosis (MS), alternative methods for identification and prioritization of variants that directly and/or indirectly play a role in disease development have become increasingly important. We were tasked with identifying possible genetic causes in a case of atypical relapsing remitting MS (RRMS) that also presented with porphyrialike symptoms and where demyelination was halted in the patient upon iron supplementation. As the patient had no parents or siblings that could be used as references for filtering exome variants, we aimed to develop a new prioritization strategy based on the combination of a predicted deleterious effect on the protein and existing knowledge of the biological roles of the genes and their contribution to relevant phenotypes.
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    Prioritization of candidate genes for a South African family with Parkinson’s disease using in-silico tools
    (Public Library of Science, 2021) Sebate, Boiketlo; Cuttler, Katelyn; Cloete, Ruben; Britz, Marcell; Christoffels, Alan; Williams, Monique; Carr, Jonathan; Bardien, Soraya
    Parkinson’s disease (PD) is a neurodegenerative disorder exhibiting Mendelian inheritance in some families. Next-generation sequencing approaches, including whole exome sequencing (WES), have revolutionized the field of Mendelian disorders and have identified a number of PD genes. We recruited a South African family with autosomal dominant PD and used WES to identify a possible pathogenic mutation. After filtration and prioritization, we found five potential causative variants in CFAP65, RTF1, NRXN2, TEP1 and CCNF. The variant in NRXN2 was selected for further analysis based on consistent prediction of deleteriousness across computational tools, not being present in unaffected family members, ethnic-matched controls or public databases, and its expression in the substantia nigra. A protein model for NRNX2 was created which provided a three-dimensional (3D) structure that satisfied qualitative mean and global model quality assessment scores. Trajectory analysis showed destabilizing effects of the variant on protein structure, indicated by high flexibility of the LNS-6 domain adopting an extended conformation. We also found that the known substrate N-acetyl-D-glucosamine (NAG) contributed to restoration of the structural stability of mutant NRXN2. If NRXN2 is indeed found to be the causal gene, this could reveal a new mechanism for the pathobiology of PD.
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    Structure based identification of novel inhibitors against ATP synthase of Mycobacterium tuberculosis : a combined in silico and in vitro study
    (Elsevier, 2019) Shahbaaz, Mohd; Cloete, Ruben; Grobbelaar, Melanie; Sampson, Samantha; Christoffels, Alan
    ENGLISH ABSTRACT: The shortcomings of conventional tuberculosis treatments resulting from the development of drug resistance in Mycobacterium tuberculosis drive a need for the formulation of novel therapeutic agents. The diarylquinoline class of drugs such as bedaquiline was recently approved for the treatment of multidrug-resistant strains of tuberculosis, primarily targeting c and ε subunits of the ATP synthases. Yet resistance to bedaquiline has already been reported. Therefore, Rv1311 was used as the target for the identification of possible inhibitors against the M. tuberculosis. The structure of Rv1311 was predicted and common feature pharmacophore models were generated which facilitated the identification of potential inhibitors in the ZINC database. The activities of the selected molecules were compared with known inhibitors of the ATP synthase using quantitative structure–activity relationship. The ZINC classified inhibitors showed comparable predicted activities with that of known inhibitors. Furthermore, the inhibitory behavior of the studied drug molecules was experimentally determined using in vitro techniques and showed the minimum inhibitory concentration as low as 25 μM. The resulted outcomes provide a deeper insight into the structural basis of Rv1311 inhibitions and can facilitate the process of drug design against tuberculosis.
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    Whole-genome sequencing for an enhanced understanding of genetic variation among South Africans
    (Nature Research (part of Springer Nature), 2017) Choudhury, Ananyo; Ramsay, Michele; Hazelhurst, Scott; Aron, Shaun; Bardien, Soraya; Botha, Gerrit; Chimusa, Emile R.; Christoffels, Alan; Gamieldien, Junaid; Sefid-Dashti, Mahjoubeh J.; Joubert, Fourie; Meintjes, Ayton; Mulder, Nicola; Ramesar, Raj; Rees, Jasper; Scholtz, Kathrine; Sengupta, Dhriti; Soodyall, Himla; Venter, Philip; Warnich, Louise; Pepper, Michael S.
    ENGLISH ABSTRACT: The Southern African Human Genome Programme is a national initiative that aspires to unlock the unique genetic character of southern African populations for a better understanding of human genetic diversity. In this pilot study the Southern African Human Genome Programme characterizes the genomes of 24 individuals (8 Coloured and 16 black southeastern Bantu-speakers) using deep whole-genome sequencing. A total of ~16 million unique variants are identified. Despite the shallow time depth since divergence between the two main southeastern Bantu-speaking groups (Nguni and Sotho-Tswana), principal component analysis and structure analysis reveal significant (p < 10−6) differentiation, and FST analysis identifies regions with high divergence. The Coloured individuals show evidence of varying proportions of admixture with Khoesan, Bantu-speakers, Europeans, and populations from the Indian sub-continent. Whole-genome sequencing data reveal extensive genomic diversity, increasing our understanding of the complex and region-specific history of African populations and highlighting its potential impact on biomedical research and genetic susceptibility to disease.