PeptX: Using Genetic Algorithms to optimize peptides for MHC binding

<p>Abstract</p> <p>Background</p> <p>The binding between the major histocompatibility complex and the presented peptide is an indispensable prerequisite for the adaptive immune response. There is a plethora of different <it>in silico </it>techniques for the prediction of the peptide binding affinity to major histocompatibility complexes. Most studies screen a set of peptides for promising candidates to predict possible T cell epitopes. In this study we ask the question vice versa: Which peptides do have highest binding affinities to a given major histocompatibility complex according to certain <it>in silico </it>scoring functions?</p> <p>Results</p> <p>Since a full screening of all possible peptides is not feasible in reasonable runtime, we introduce a heuristic approach. We developed a framework for Genetic Algorithms to optimize peptides for the binding to major histocompatibility complexes. In an extensive benchmark we tested various operator combinations. We found that (1) selection operators have a strong influence on the convergence of the population while recombination operators have minor influence and (2) that five different binding prediction methods lead to five different sets of "optimal" peptides for the same major histocompatibility complex. The consensus peptides were experimentally verified as high affinity binders.</p> <p>Conclusion</p> <p>We provide a generalized framework to calculate sets of high affinity binders based on different previously published scoring functions in reasonable runtime. Furthermore we give insight into the different behaviours of operators and scoring functions of the Genetic Algorithm.</p

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Polymorphisms in Multiple Genes Contribute to the Spontaneous Mitochondrial Genome Instability of Saccharomyces cerevisiae S288C Strains

The mitochondrial genome (mtDNA) is required for normal cellular function; inherited and somatic mutations in mtDNA lead to a variety of diseases. Saccharomyces cerevisiae has served as a model to study mtDNA integrity, in part because it can survive without mtDNA. A measure of defective mtDNA in S. cerevisiae is the formation of petite colonies. The frequency at which spontaneous petite colonies arise varies by ∼100-fold between laboratory and natural isolate strains. To determine the genetic basis of this difference, we applied quantitative trait locus (QTL) mapping to two strains at the opposite extremes of the phenotypic spectrum: the widely studied laboratory strain S288C and the vineyard isolate RM11-1a. Four main genetic determinants explained the phenotypic difference. Alleles of SAL1, CAT5, and MIP1 contributed to the high petite frequency of S288C and its derivatives by increasing the formation of petite colonies. By contrast, the S288C allele of MKT1 reduced the formation of petite colonies and compromised the growth of petite cells. The former three alleles were found in the EM93 strain, the founder that contributed ∼88% of the S288C genome. Nearly all of the phenotypic difference between S288C and RM11-1a was reconstituted by introducing the common alleles of these four genes into the S288C background. In addition to the nuclear gene contribution, the source of the mtDNA influenced its stability. These results demonstrate that a few rare genetic variants with individually small effects can have a profound phenotypic effect in combination. Moreover, the polymorphisms identified in this study open new lines of investigation into mtDNA maintenance

Germline Gene Editing in Chickens by Efficient CRISPR-Mediated Homologous Recombination in Primordial Germ Cells.

The CRISPR/Cas9 system has been applied in a large number of animal and plant species for genome editing. In chickens, CRISPR has been used to knockout genes in somatic tissues, but no CRISPR-mediated germline modification has yet been reported. Here we use CRISPR to target the chicken immunoglobulin heavy chain locus in primordial germ cells (PGCs) to produce transgenic progeny. Guide RNAs were co-transfected with a donor vector for homology-directed repair of the double-strand break, and clonal populations were selected. All of the resulting drug-resistant clones contained the correct targeting event. The targeted cells gave rise to healthy progeny containing the CRISPR-targeted locus. The results show that gene-edited chickens can be obtained by modifying PGCs in vitro with the CRISPR/Cas9 system, opening up many potential applications for efficient genetic modification in birds

Proteins that carry dual targeting signals can act as tethers between peroxisomes and partner organelles.

Peroxisomes are organelles with crucial functions in oxidative metabolism. To correctly target to peroxisomes, proteins require specialized targeting signals. A mystery in the field is the sorting of proteins that carry a targeting signal for peroxisomes and as well as for other organelles, such as mitochondria or the endoplasmic reticulum (ER). Exploring several of these proteins in fungal model systems, we observed that they can act as tethers bridging organelles together to create contact sites. We show that in Saccharomyces cerevisiae this mode of tethering involves the peroxisome import machinery, the ER-mitochondria encounter structure (ERMES) at mitochondria and the guided entry of tail-anchored proteins (GET) pathway at the ER. Our findings introduce a previously unexplored concept of how dual affinity proteins can regulate organelle attachment and communication

Growth curves of CRISPR progeny.

<p>Eight heterozygous IgH KO6B females and eight control females were weighed weekly for 8 weeks.</p

Cre recombination of CRISPR-targeted loxP site.

<p>A. Diagram of the targeted IgH locus before and after Cre recombination. A forward primer upstream of the CRISPR-targeted loxP site was used with two different reverse primers downstream of the loxP site in the JH-KO cassette. In the non-recombined allele, the forward and reverse primers are separated by about 28kb on the chromosome. After Cre recombination, a single loxP site and the promoterless neo gene remain, and the primers are either 1.6 or 2kb apart, which amplifies readily. B. PCR of recombined cells. Cre +: gDNA template from 1783–9 cells transfected with Cre; Cre -, parental 1783–9 cells; JH-KO, gDNA from a heterozygous JH-KO bird; NTC, no template control.</p