Biology subjects

Sulkowska, J. I.

Publications and source records attributed to Sulkowska, J. I..

9 recordsLinked to original sources

bioRxiv2025

Multi-barrier unfolding of the double-knotted protein, TrmD-Tm1570, revealed by single-molecule force spectroscopy and molecular dynamics

The doubly knotted motif is one of the least expected features in proteins, occurring in both globular and transmembrane forms. Here, we focus on globular protein members of the methyltransferase family: the TrmD-Tm1570 protein, which contains two deep 31 knots, and the single-knotted proteins TrmD and Tm1570, all from Calditerrivibrio nitroreducens. Using various biophysical experimental techniques and computer simulations with AI-based methods, we studied their thermal and thermodynamic stability, as well as their mechanical unfolding. Based on molecular dynamics (MD) simulations, with the Structure-Based C Model (SBM-C) and UNRES (coarse-grained), we show that native contacts alone are not sufficient to fold double-knotted proteins. However, native contacts are sufficient to fold the single-knotted proteins TrmD and Tm1570 into their native conformations. Using the same model, we identified four possible unfolding and untying pathways, in which each domain can self-tie independently at some stage of the process. Optical tweezers (OT) experiments show that this process is also reversible, although the stretched state remains knotted. In addition, we observed higher thermal and mechanical stability in Tm1570 compared with TrmD, which is partly attributable to the position of the knot core. Overall, our results suggest that double-knotted protein from the SPOUT family can only partially self-fold, and that full knotting may require the assistance of a chaperone.

biophysics↗

bioRxiv2025

Universe of Lasso Proteins: Exploring the limit of entanglement and folding landscape of proteins predicted by AlphaFold

AO_SCPLOWBSTRACTC_SCPLOWKnots and lasso topology represent a class of natural motifs found in proteins which are characterized by a threaded structure. Proteins with a lasso motif represent a macroscopic version of the peptide lasso, which are known for their high stability and offer tremendous potential for the development of novel therapeutics. Here, based on AlphaFold, we have shown the limit of topological complexity of naturally occurring protein structures with cysteine bridges. Based on 176 million high confidence (pLDDT > 70) AlphaFold-predicted protein models and a detailed analysis of the conservation of the motif in a family, we found four new lasso motifs, including L4 and LS4LS3 topologies, and the first examples of knotted lasso proteins: L1K31 and L3#K31. We show that in the case of natural proteins, there are no lassos with 5 threadings but there exist some with 6. Families possessing proteins with more than 6 threadings did not exceed the conservation threshold of 10%. Moreover, we propose a probable folding mechanism for the LS4LS3 lasso motif, enhancing our view on protein folding and stability. This work expands the topological space of lasso type motifs in proteins but also suggests that more complex structures could be unfavorable for proteins. HighlightsO_LIDiscovery of novel non-trivial lasso motifs: the L4, supercoiling of both tails LS4LS3, and the first knotted lasso proteins: L1K31 and L3#K31. C_LIO_LIThe knotted lasso motifs are in membrane proteins. C_LIO_LILassos topologies with 5 or more crossings are not conserved in protein families, and more complex motifs do not exist C_LIO_LI472 new InterPro entries with a high probability of non-trivial lasso motif C_LIO_LIPotential folding pathway for proteins with complex supercoiled lasso motif LS4LS3 C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=71 SRC="FIGDIR/small/644650v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@9c3cedorg.highwire.dtl.DTLVardef@163f941org.highwire.dtl.DTLVardef@811e31org.highwire.dtl.DTLVardef@e53de5_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Knotted artifacts in predicted 3D RNA structures

Unlike proteins, RNAs deposited in the Protein Data Bank do not contain topological knots. Recently, admittedly, the first trefoil knot and some lasso-type conformations have been found in experimental RNA structures, but these are still exceptional cases. Meanwhile, algorithms predicting 3D RNA models have happened to form knotted structures not so rarely. Interestingly, machine learning-based predictors seem to be more prone to generate knotted RNA folds than traditional methods. A similar situation is observed for the entanglements of structural elements. In this paper, we analyze all models submitted to the CASP15 competition in the 3D RNA structure prediction category. We show what types of topological knots and structure element entanglements appear in the submitted models and highlight what methods are behind the generation of such conformations. We also study the structural aspect of susceptibility to entanglement. We suggest that predictors take care of an evaluation of RNA models to avoid publishing structures with artifacts, such as unusual entanglements, that result from hallucinations of predictive algorithms. Author summaryO_LI3D RNA structure prediction contests such as CASP and RNA-Puzzles lack measures for topology-wise evaluation of predicted models. Thus, predictors happen to submit potentially inappropriate conformations, for example, containing entanglements that are prediction artifacts. C_LIO_LIAutomated identification of entanglements in 3D RNA structures is computationally hard. Distinguishing correct from incorrectly entangled conformations is not trivial and often requires expert knowledge. C_LIO_LIWe analyzed 3D RNA models submitted to CASP15 and found that all entanglements in these models are artifacts. C_LIO_LICompared to non-ML, machine learning-based methods are more prone to generating entanglements that are not present in natural RNAs. C_LIO_LITo increase the reliability of 3D RNA structure prediction, it is necessary to reject abnormally entangled structures in the modeling stage. C_LI

bioinformatics↗

bioRxiv2023

Knot or Not? Sequence-Based Identification of Knotted Proteins With Machine Learning

Knotted proteins, although scarce, are crucial structural components of certain protein families, and their roles remain a topic of intense research. Capitalizing on the vast collection of protein structure predictions offered by AlphaFold, this study computationally examines the entire UniProt database to create a robust dataset of knotted and unknotted proteins. Utilizing this dataset, we develop a machine learning model capable of accurately predicting the presence of knots in protein structures solely from their amino acid sequences, with our best-performing model demonstrating a 98.5% overall accuracy. Unveiling the sequence factors that contribute to knot formation, we discover that proteins predicted to be unknotted from known knotted families are typically non-functional fragments missing a significant portion of the knot core. The study further explores the significance of the substrate binding site in knot formation, particularly within the SPOUT protein family. Our findings spotlight the potential of machine learning in enhancing our understanding of protein topology and propose further investigation into the role of knotted structures across other protein families. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/556468v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1466077org.highwire.dtl.DTLVardef@1674829org.highwire.dtl.DTLVardef@1b283a5org.highwire.dtl.DTLVardef@e0e962_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

bioRxiv2023

Proteins containing 6-crossing knot types andtheir folding pathways

Studying complex protein knots can provide new insights into potential knot folding mechanisms and other fundamental aspects of why and how proteins knot. This paper presents results of a systematic analysis of the 3D structure of proteins with 6-crossings knots predicted by the artificial intelligence program AlphaFold 2. Furthermore, using a coarse-grained native based model, we found that three representative proteins can self tie to a 63 knot, the most complex knot found in a protein thus far. Because it is not a twist knot, the 63 knot cannot be folded via a simple mechanism involving the threading of a single loop. Based on successful trajectories for each protein, we determined that the 63 knot is formed after folding a significant part of the protein backbone to the native conformation. Moreover, we found that there are two distinct knotting mechanisms, which are described here. Also, building on a loop flipping theory developed earlier, we present two new theories of protein folding involving the creation and threading of two loops, and explain how our theories can describe the successful folding trajectories for each of the three representative 63-knotted proteins.

biophysics↗

bioRxiv2023

Nucleolar Essential Protein 1 (Nep1): Elucidation of Enzymatic Catalysis Mechanism by Combined Molecular Dynamics Simulation and Quantum Chemical Calculations

Nep1 is a protein essential for the formation of the eukaryotic and archaeal small ribosomal subunit. It is an enzyme responsible for the site-specific SAM-dependent methylation of pseudouridine ({Psi}) during the pre-rRNA processing. It possesses a non-trivial topology, namely, a 31 knot in the active site. Herein, we investigate the structure and mechanism of catalysis of Nep1 using a combination of bioinformatics, computational, and experimental methods. In particular, we address the issue of seemingly unfeasible deprotonation of {Psi} nucleobase in the active site of Nep1 by a distant aspartate residue (e.g., D101 in Nep1 of S. cerevisiae). Sequence alignment analysis across different organisms identifies a conserved serine/threonine residue that may play a role of a proton-transfer mediator (e.g., S233 in Nep1 from S. cerevisiae), facilitating the reaction. Two enzyme-substrate complexes, one based on an available crystal structure and the other generated by molecular docking, of representative eukaryotic (from S. cerevisiae) and archaeal (from A. fulgidus) Nep1 homologs are subjected to molecular dynamics (MD) simulations. The resulting trajectories confirm that the hydroxyl-containing amino acid can indeed adopt a position suitable for proton-shuttling, with the OH group located in between the proton donor and acceptor. However, during the MD simulations, a water molecule emerges from arrangements of the active site, which can assume the role of the proton-transfer mediator instead. To discern between these two alternative pathways, we evaluate the possible methylation mechanisms by quantum-chemical calculations based on density functional theory, using the cluster approach. The obtained energy profiles indicate that the most facile course of the reaction for both the yeast and archaeal enzymes is to engage the water molecule. These results are corroborated by agreement of the computed energy barriers with experimentally measured enzyme kinetics. Moreover, mutational studies show that, while aspartate D101 is crucial for the catalytic activity, serine S233 is irrelevant in this context, indirectly supporting the water-mediated proton transfer. Our findings comprehensively elucidate the mode of action of Nep1 and provide implication for understanding the catalytic mechanisms of other enzymes that involve a proton transfer in the active site over extended distances.

biophysics↗

bioRxiv2023

First crystal structure of double knotted protein TrmD-Tm1570 - inside from degradation perspective

Herein, we present the first crystal structure of a double knotted protein TrmD-Tm1570 from Calditerrivibrio nitroreducens, as well the X-ray structure of each sub-domain. The protein consists of two domains TrmD and Tm1570, each embedding a single trefoil knot, which can function on their own. TrmD-Tm1570 forms a compact homodimeric complex. This protein represents one of 296 possible doubly knotted proteins from SPOUT family. Based on TrmD-Tm1570 from Calditerrivibrio nitroreducens we show that a double knotted protein can be fully degraded by the ClpXP degradation system, as well as its individual domains. We used numerical simulations to explain the difference in the speed of degradation. The derived kinetic parameters for the degradation process are comparable to the experimental data found for unknotted polypeptide chains.

biophysics↗

bioRxiv2022

New 63 knot and other knots in human proteome from AlphaFold predictions

AlphaFold is a new, highly accurate machine learning protein structure prediction method that outperforms other methods. Recently this method was used to predict the structure of 98.5% of human proteins. We analyze here the structure of these AlphaFold-predicted human proteins for the presence of knots. We found that the human proteome contains 65 robustly knotted proteins, including the most complex type of a knot yet reported in proteins. That knot type, denoted 63 in mathematical notation, would necessitate a more complex folding path than any knotted proteins characterized to date. In some cases AlphaFold structure predictions are not highly accurate, which either makes their topology hard to verify or results in topological artifacts. Other structures that we found, which are knotted, potentially knotted, and structures with artifacts (knots) we deposited in a database available at: https://knotprot.cent.uw.edu.pl/alphafold.

molecular biology↗

bioRxiv2019

Restriction of S-adenosylmethionine conformational freedom by knotted protein binding sites

S-adenosylmethionine (SAM) is one of the most important enzyme substrates. It is vital for the function of various proteins, including large group of methyltransferases (MTs). Intriguingly, some bacterial and eukaryotic MTs, while catalysing the same reaction, possess significantly different topologies, with the former being a knotted one. Here, we conducted a comprehensive analysis of SAM conformational space and factors that affect its vastness. We investigated SAM in two forms: free in water (via NMR studies and explicit solvent simulations) and bound to proteins (based on all data available in the PDB). We identified structural descriptors - angles which show the major differences in SAM conformation between unknotted and knotted methyltransferases. Moreover, we report that this is caused mainly by a characteristic for knotted MTs tight binding site formed by the knot and the presence of adenine-binding loop. Additionally, we elucidate conformational restrictions imposed on SAM molecules by other protein groups in comparison to conformational space in water. Author summaryThe topology of a folded polypeptide chain has great impact on the resulting protein function and its interaction with ligands. Interestingly, topological constraints appear to affect binding of one of the most ubiquitous substrates in the cell, S-adenosylmethionine (SAM), to its target proteins. Here, we demonstrate how binding sites of specific proteins restrict SAM conformational freedom in comparison to its unbound state, with a special interest in proteins with non-trivial topology, including an exciting group of knotted methyltransferases. Using a vast array of computational methods combined with NMR experiments, we identify key structural features of knotted methyltransferases that impose unorthodox SAM conformations. We compare them with the characteristics of standard, unknotted SAM binding proteins. These results are significant for understanding differences between analogous, yet topologically different enzymes, as well as for future rational drug design.

biophysics↗