Biology subjects

Bittrich, S.

Publications and source records attributed to Bittrich, S..

3 recordsLinked to original sources

bioRxiv2018

Application of an Interpretable Classification Model on Early Folding Residues during Protein Folding

BackgroundMachine learning strategies are prominent tools for data analysis. Especially in life sciences, they have become increasingly important to handle the growing datasets collected by the scientific community. Meanwhile, algorithms improve in performance, but also gain complexity, and tend to neglect interpretability and comprehensiveness of the resulting models.\n\nResultsGeneralized Matrix Learning Vector Quantization (GMLVQ) is a supervised, prototype-based machine learning method and provides comprehensive visualization capabilities not present in other classifiers which allow for a fine-grained interpretation of the data. In contrast to commonly used machine learning strategies, GMLVQ is well-suited for imbalanced classification problems which are frequent in life sciences. We present a Weka plug-in implementing GMLVQ. The feasibility of GMLVQ is demonstrated on a dataset of Early Folding Residues (EFR) that have been shown to initiate and guide the protein folding process. Using 27 features, an area under the receiver operating characteristic of 76.6% was achieved which is comparable to other state-of-the-art classifiers.\n\nConclusionsThe application on EFR prediction demonstrates how an easy interpretation of classification models can promote the comprehension of biological mechanisms. The results shed light on the special features of EFR which were reported as most influential for the classification: EFR are embedded in ordered secondary structure elements and they participate in networks of hydrophobic residues. Visualization capabilities of GMLVQ are presented as we demonstrate how to interpret the results.

bioinformatics↗

bioRxiv2018

Functional and Early Folding Residues are separated in proteins to increase evolvability and robustness

The three-dimensional structure of proteins captures evolutionary ancestry, and serves as starting point to understand the origin of diseases. Proteins adopt their structure autonomously by the process of protein folding. Over the last decades, the folding process of several proteins has been studied with temporal and spatial resolution which allowed the identification of so-called Early Folding Residues (EFR) in the folding process. These structurally relevant residues become affected early in the folding process and initiate the formation of secondary structure elements and guide their assembly.\n\nUsing a dataset of 30 proteins and 3,337 residues provided by the Start2Fold database, discriminative features of EFR were identified by a systematical characterization. Therefore, proteins were represented as graphs in order to analyze topological descriptors of EFR. They constitute crucial connectors of protein regions which are distant at sequence level. Especially, these residues exhibit a high number of non-covalent contacts such as hydrogen bonds and hydrophobic interactions. This tendency also manifest as energetically stable local regions in a knowledge-based potential. Conclusively, these features are not only characteristic for EFR but also differ significantly with respect to functional residues. This unveils a split between structurally and functionally relevant residues in proteins which can drastically improve their evolvability and robustness.\n\nThe characteristics of EFR cannot be attributed to trivial features such as the accessible surface area. Thus, the presented features are novel descriptors for EFR of the folding process. Potentially, these features can be used to design classifiers to predict EFR from structure or to implement structure quality assessment programs. The shown division of labor between functional and EFR has implications for the prediction of mutation effects as well as protein design and can provide insights into the evolution of proteins. Finally, EFR allow to further the understanding of the protein folding process due to their pivotal role.\n\nAuthor summaryProteins are chains of amino acids which adopt a three-dimensional structure and are then able to catalyze chemical reactions or propagate signals in organisms. Without external influence, most proteins fold into their correct structure, and a small number of Early Folding Residues (EFR) have been shown to become affected at the very start of the process. We demonstrated that these residues are located in energetically stable local conformations. EFR are in contact to many other residues of a protein and act as hubs between sequentially distant regions of a proteins. These distinct characteristics can give insights into what causes certain residues to initiate and guide the folding process. Furthermore, it can help our understanding regarding diseases such as Alzheimers or amyotrophic lateral sclerosis which are the result of protein folding gone wrong. We further found that the structurally relevant EFR are almost exclusively non-functional. Proteins separate structure and function, which increases evolvability and robustness and gives guidance for the artificial design of proteins.

bioinformatics↗

bioRxiv2017

Backbone brackets and arginine tweezers delineate class I and class II aminoacyl tRNA synthetases

The origin of the machinery that realizes protein biosynthesis in all organisms is still unclear. One key component of this machinery are aminoacyl tRNA synthetases (aaRS), which ligate tRNAs to amino acids while consuming ATP. Sequence analyses revealed that these enzymes can be divided into two complementary classes. Both classes differ significantly on a sequence and structural level, feature different reaction mechanisms, and occur in diverse oligomerization states. The one unifying aspect of both classes is their function of binding ATP. We identified Backbone Brackets and Arginine Tweezers as most compact ATP binding motifs characteristic for each Class. Geometric analysis shows a structural rearrangement of the Backbone Brackets upon ATP binding, indicating a general mechanism of all Class I structures. Regarding the origin of aaRS, the Rodin-Ohno hypothesis states that the peculiar nature of the two aaRS classes is the result of their primordial forms, called Protozymes, being encoded on opposite strands of the same gene. Backbone Brackets and Arginine Tweezers were traced back to the proposed Protozymes and their more efficient successors, the Urzymes. Both structural motifs can be observed as pairs of residues in contemporary structures and it seems that the time of their addition, indicated by their placement in the ancient aaRS, coincides with the evolutionary trace of Proto- and Urzymes.\n\nAuthor summaryAminoacyl tRNA synthetases (aaRS) are primordial enzymes essential for interpretation and transfer of genetic information. Understanding the origin of the peculiarities observed with aaRS can explain what constituted the earliest life forms and how the genetic code was established. The increasing amount of experimentally determined three-dimensional structures of aaRS opens up new avenues for high-throughput analyses of molecular mechanisms. In this study, we present an exhaustive structural analysis of ATP binding motifs. We unveil an oppositional implementation of enzyme substrate binding in each aaRS Class. While Class I binds via interactions mediated by backbone hydrogen bonds, Class II uses a pair of arginine residues to establish salt bridges to its ATP ligand. We show how nature realized the binding of the same ligand species with completely different mechanisms. In addition, we demonstrate that sequence or even structure analysis for conserved residues may miss important functional aspects which can only be revealed by ligand interaction studies. Additionally, the placement of those key residues in the structure supports a popular hypothesis, which states that prototypic aaRS were once coded on complementary strands of the same gene.

bioinformatics↗