Biology subjects

Malliavin, T. E.

Publications and source records attributed to Malliavin, T. E..

5 recordsLinked to original sources

bioRxiv2024

Influence of stereochemistry in a local approach for calculating protein conformations

Protein structure prediction is usually based on the use of local conformational information coupled with long-range distance restraints. Such restraints can be derived from the knowledge of a template structure or the analysis of protein sequence alignment in the framework of models arising from the physics of disordered systems. The accuracy of approaches based on sequence alignment, however, is limited in the case where the number of aligned sequences is small. Here we derive protein conformations using only local conformations knowledge by means of the interval Branch-and-Prune algorithm. The computation efficiency is directly related to the knowledge of stereochemistry (bond angle and{omega} values) along the protein sequence, and in particular to the variations of the torsion angle{omega} . The impact of stereochemistry variations is particularly strong in the case of protein topologies defined from numerous long-range restraints, as in the case of protein of {beta} secondary structures. The systematic enumeration of the conformations improves the efficiency of the calculations. The analysis of DNA codons permits to connect the variations of torsion angle{omega} to the positions of rare DNA codons.

bioinformatics↗

bioRxiv2024

Conformational Space of the Translocation Domain of Botulinum Toxin: Atomistic Modeling and Mesoscopic Description of the Coiled-Coil Helix Bundle

The toxicity of botulinum multi-domain neurotoxins (BoNTs) arises from a sequence of molecular events, in which the translocation of the catalytic domain through the membrane of a neurotransmitter vesicle plays a key role. A structural study (Lam et al., Nat. Comm., 2018) of the translocation domain of BoNT suggests that the interaction with the membrane is driven by the transition of an helical switch towards a {beta} hairpin. Atomistic simulations in conjunction with the mesoscopic Twister model are used to investigate the consequences of this proposition for the toxin-membrane interaction. The conformational mobilities of the domain as well as the effect of the membrane, implicitly examined by comparing water and water-ethanol solvents, lead to the conclusion that the transition of the switch modifies the internal dynamics and the effect of membrane hydrophobicity on the whole protein. The central two helices, helix 1 and helix 2, forming two coiled-coil motifs, are analyzed using the Twister model, in which the initial deformation of the membrane by the protein is caused by the presence of local torques arising from asymmetric positions of hydrophobic residues. Different torque distributions are observed depending on the switch conformations and permit to propose an origin for the mechanism opening the membrane.

biophysics↗

bioRxiv2022

In silico conformational features of botulinum toxins A1 and E1 according to the intraluminal acidification

Although the botulinum neurotoxins (BoNTs) are among the most toxic compounds found in nature, their molecular mechanism of action is far from being elucidated. A key event is the conformational transition due to the acidification of the interior of synaptic vesicles, and leading to the translocation of the BoNT catalytic domain into the neuronal cytosol. To investigate these conformational variations, homology modelling and atomistic simulations are combined to explore the internal dynamics of the subtypes BoNT/A1, the most-used in medical applications, and BoNT/E1, the most kinetically efficient. This first simulation study of di-chain BoNTs in closed and open states includes the effects of neutral and acidic pH. The conformational mobility is driven by domains displacements; the ganglioside binding site in the receptor binding domain, the translocation domain (HCNT) switch and the belt helix visit multiple conformations depending on the primary sequence and on the pH. Fluctuations of the belt helix are observed for closed conformations of the toxins and at acidic pH, and patches of more accessible residues appear in the same conditions in the core translocation domain HCNT. These findings suggest that during translocation, the larger mobility of belt could be transmitted to HCNT, leading to a favorable interaction of HCNT residues with the non-polar membrane environment. Key ContributionThe molecular dynamics simulations presented here provide a structural and functional annotation of full-length BoNTs composed by two distinct protein chains. Two different conformations (open and closed) as well as two different protonation states, corresponding to acidic and neutral pH, have been considered. Results from the present work supports a model of mobility in which the individual domains fluctuate around stable conformations and the overall structure mobility arise from relative displacements of the domains.

neuroscience↗

bioRxiv2021

Computational and biochemical analysis of type IV Pilus dynamics and stability

Type IV pili (T4P) are distinctive dynamic filaments at the surface of many bacteria that can rapidly extend, retract and withstand strong forces. T4P are important virulence factors in many human pathogens, including Enterohemorrhagic Escherichia coli (EHEC). The structure of the EHEC T4P has been determined by integrating Nuclear Magnetic Resonance (NMR) and cryo-electron microscopy data. To better understand pilus assembly, stability and function, we performed a total of 108 s all-atom molecular dynamics simulations of wild-type and mutant T4P. Extensive characterization of the conformational landscape of T4P in different conditions of temperature, pH and ionic strength was complemented by targeted mutagenesis and biochemical analyses. Our simulations and NMR experiments revealed a conserved set of residues defining a novel calcium-binding site at the interface between three pilin subunits. Calcium binding enhanced T4P stability ex vivo and in vitro, supporting the role of this binding site as a potential pocket for drug design.

biochemistry↗

bioRxiv2019

Systematic exploration of protein conformational space using a Distance Geometry approach

The optimisation approaches classically used during the determination of protein structure encounter various diffculties, specially when the size of the conformational space is large. Indeed, in such case, algorithmic convergence criteria are more difficult to set up. Moreover, the size of the search space makes it difficult to achieve a complete exploration. The interval Branch-and-Prune (iBP) approach, based on the reformulating of the Distance Geometry Problem (DGP) provides a theoretical frame for the generation of protein conformations, by systematically sampling the conformational space. When an appropriate subset of inter-atomic distances is known exactly, this worst-case exponential-time algorithm is provably complete and fixed-parameter tractable. These guarantees, however, immediately disappear as distance measurement errors are introduced. Here we propose an improvement of this approach: the threading-augmented interval Branch-and-Prune (TAiBP), where the combinatorial explosion of the original iBP approach arising from its exponential complexity is alleviated by partitioning the input instances into consecutive peptide fragments and by using Self-Organizing Maps (SOMs) to obtain clusters of similar solutions. A validation of the TAiBP approach is presented here on a set of proteins of various sizes and structures. The calculation inputs are: a uniform covalent geometry extracted from force field covalent terms, the backbone dihedral angles with error intervals, and a few long-range distances. For most of the proteins smaller than 50 residues and interval widths of 20{degrees}, the TAiBP approach yielded solutions with RMSD values smaller than 3 [A] with respect to the initial protein conformation. The efficiency of TAiBP approach for proteins larger than 50 residues will require the use of non-uniform covalent geometry, and may have benefits from the recent development of residue-specific force-fields.

bioinformatics↗