@article {48447, title = {Governing dynamics and preferential binding of the AXH domain influence the aggregation pathway of Ataxin-1}, journal = {Proteins-Structure Function and Bioinformatics}, volume = {91}, year = {2023}, month = {MAR}, pages = {380-394}, type = {Article}, abstract = {

The present state of understanding the mechanism of Spinocerebellar Ataxia-1, a fatal neurodegenerative disease linked to the protein Ataxin-1 (ATXN1), is baffled by a set of self-contradictory, and hence, inconclusive observations. This fallacy poses a bottleneck to the effective designing of curable drugs as the field is currently missing the specific druggable site. To understand the fundamentals of pathogenesis, we tried to decipher the intricacies of the extremely complicated landscape by targeting the relevant species that supposedly dictate the structure-function paradigm. The atomic-level description and characterization of the dynamism of the systems reveal the existence of structural polymorphism in all the leading stakeholders of the overall system. The very existence of conformational heterogeneity in every species creates numerous possible combinations of favorable interactions because of the variability in segmental cross-talks and hence claims its role in the choice of routes between functional activity and dysfunctional disease-causing aggregation. Despite this emergent configurational diversity, there is a common mode of operative intermolecular forces that dictates the extent of stability of all the multimeric complexes due to the localized population of a specific type of residue. The present research proposes a dynamic switch mechanism between aggregability and functional activity, based on the logical interpretation of the estimated variables, which is practically dictated by the effective concentration of the interacting species involved in the cell.

}, keywords = {Ataxin-1, molecular dynamics simulation, neurodegenerative diseases, Protein aggregation, protein misfolding disorders}, issn = {0887-3585}, doi = {10.1002/prot.26436}, author = {Tammara, Vaishnavi and Das, Atanu} } @article {48711, title = {Molecular mechanism of PSMa3 aggregation: a new view}, journal = {Journal of Physical Chemistry B}, volume = {127}, year = {2023}, month = {SEP}, pages = {8317-8330}, type = {Article}, abstract = {

The emergence of a novel cross-alpha fibrillar structure, unlike the commonly observed sequence-independent cross-beta one, of a 22-residue bacterial virulent amphipathic alpha-helical peptide of the phenol soluble modulin (PSM) family, PSM alpha 3, with many deleterious effects on human life, has infused uncertainty to the paradigm of the intrinsically polymorphic, multivariate, multiphasic, and cross-sequence-cross-disease entangled protein aggregation landscape and hence on the identity of the therapeutic target. We, here, deconvolute the factors contributing to the genesis and hence the transition of lower to higher order aggregates of PSM alpha 3 in its natural state and three noncanonical designed variants using conventional and enhanced sampling approach-based atomistic simulations. PSM alpha 3 shows structural polymorphism with nominal alpha-helicity, substantial beta-propensity, and dominant random-coil features, irrespective of the extent of aggregation. Moreover, the individual features of the overall amphipathicity operate alternatively depending on the extent and organization of aggregation; the dominance gradually moves from charged to hydrophobic residues with the progressive generation of higher order aggregates (dimer to oligomer to fibril) and with increasing orderedness of the self-assembled construct (oligomer vs dimer/fibril). Similarly, the contribution of interchain salt bridges decreases with increasing order of aggregation (dimer to oligomer to fibril). However, the intrachain salt bridges consistently display their role in all phases of aggregation. Such phase-independent features also include equivalent roles of electrostatic and van der Waals forces on intrachain interactions, sole contribution of van der Waals forces on interchain cross-talk, and negligible peptide-water relationship. Finally, we propose a conjugate peptide-based aggregation suppressor having a single-point proline mutation.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.3c03806}, author = {Tammara, Vaishnavi and Das, Atanu} } @article {49250, title = {Deciphering the monomeric and dimeric conformational landscapes of the full-length TDP-43 and the impact of the C-terminal domain}, journal = {ACS Chemical Neuroscience}, volume = {15}, year = {2024}, month = {NOV}, pages = {4305-4321}, type = {Article}, abstract = {

The aberrant aggregation of TAR DNA-binding protein 43 kDa (TDP-43) in cells leads to the pathogenesis of multiple fatal neurodegenerative diseases. Decoding the proposed initial transition between its functional dimeric and aggregation-prone monomeric states can potentially design a viable therapeutic strategy, which is presently limited by the lack of structural detail of the full-length TDP-43. To achieve a complete understanding of such a delicate phase space, we employed a multiscale simulation approach that unearths numerous crucial features, broadly summarized in two categories: (1) state-independent features that involve inherent chain collapsibility, rugged polymorphic landscape dictated by the terminal domains, high beta-sheet propensity, structural integrity preserved by backbone-based intrachain hydrogen bonds and electrostatic forces, the prominence of the C-terminal domain in the intrachain cross-domain interfaces, and equal participation of hydrophobic and hydrophilic (charged and polar) residues in cross-domain interfaces; and (2) dimerization-modulated characteristics that encompass slower collapsing dynamics, restricted polymorphic landscape, the dominance of side chains in interchain hydrogen bonds, the appearance of the N-terminal domain in the dimer interface, and the prominence of hydrophilic (specifically polar) residues in interchain homo- and cross-domain interfaces. In our work, the ill-known C-terminal domain appears as the most crucial structure-dictating domain, which preferably populates a compact conformation with a high beta-sheet propensity in its isolated state stabilized by intrabackbone hydrogen bonds, and these signatures are comparatively faded in its integrated form. Validation of our simulated observables by a complementary spectroscopic approach on multiple counts ensures the robustness of the computationally predicted features of the TDP-43 aggregation landscape.

}, keywords = {chain collapsibility, domain-wisefluctuation, electrostatic dominance, hydrogen bond switchability, long-range crosstalk, persistent beta-character, protagonistic C-terminal domain, rugged phase space}, issn = {1948-7193}, doi = {10.1021/acschemneuro.4c00557}, author = {Tammara, Vaishnavi and Doke, Abhilasha A. and Jha, Santosh Kumar and Das, Atanu} } @article {48981, title = {Flagellar motor protein-targeted search for the druggable site of Helicobacter pylori}, journal = {Physical Chemistry Chemical Physics }, volume = {26}, year = {2024}, month = {JAN }, pages = {2111-2126}, type = {Article}, abstract = {

The deleterious impact of Helicobacter pylori (H. pylori) on human health is contingent upon its ability to create and sustain colony structure, which in turn is dictated by the effective performance of flagella - a multi-protein rotary nanodevice. Hence, to design an effective therapeutic strategy against H. pylori, we here conducted a systematic search for an effective druggable site by focusing on the structure-dynamics-energetics-stability landscape of the junction points of three 1 : 1 protein complexes (FliF(C)-FliG(N), FliG(M)-FliM(M), and FliY(C)-FliN(C)) that contribute mainly to the rotary motion of the flagella via the transformation of information along the junctions over a wide range of pH values operative in the stomach (from neutral to acidic). We applied a gamut of physiologically relevant perturbations in the form of thermal scanning and mechanical force to sample the entire quasi - and non-equilibrium conformational spaces available for the protein complexes under neutral and acidic pH conditions. Our perturbation-induced magnification of conformational distortion approach identified pH-independent protein sequence-specific evolution of precise thermally labile segments, which dictate the specific thermal unfolding mechanism of each complex and this complex-specific pH-independent structural disruption notion remains consistent under mechanical stress as well. Complementing the above observations with the relative rank-ordering of estimated equilibrium binding free energies between two protein sequences of a specific complex quantifies the extent of structure-stability modulation due to pH alteration, rationalizes the exceptional stability of H. pylori under acidic pH conditions, and identifies the pH-independent complex-sequence-segment-residue diagram for targeted drug design.

}, issn = {1463-9076}, doi = {10.1039/d3cp05024f}, author = {Tammara, Vaishnavi and Angrover, Ruchika and Sirur, Disha and Das, Atanu} } @article {49188, title = {Self-consistent molecular mechanism of β2-microglobulin aggregation}, journal = {Journal of Physical Chemistry B}, volume = {128}, year = {2024}, month = {DEC}, pages = {12425-12442}, type = {Article}, abstract = {

Despite the consensus on the origin of dialysis-related amyloidosis (DRA) being beta(2)-microglobulin (beta(2)m) aggregation, the debate on the underlying mechanism persists because of the continuous emergence of beta(2)m variant- and pH-dependent contradictory results. By characterizing the native monomeric (initiation) and aggregated fibrillar (termination) states of beta(2)m via a combination of two enhanced sampling approaches, we here propose a mechanism that explains the heterogeneous behavior of wild-type (WT) and pathogenic (V27M and D76N) beta(2)m variants in physiological and disease-pertinent acidic pH environments. It appears that the higher retainment of monomeric native folds at neutral pH (native-like) distinguishes pathogenic beta(2)m mutants from the WT (moderate loss). However, at acidic pH, all three variants behave similarly in producing a substantial amount of partially unfolded states (conformational switch, propensity), though with different extents (WT \< V27M \< D76N). Whereas at the fibrillar end, all beta(2)m variants display a pH-dependent protofilament separation pathway and a higher protofilament binding affinity (stability) at acidic pH, where the relative order of binding affinity (WT \< V27M \< D76N) remains consistent with pH modulation. Combining these observations, we conclude that beta(2)m variants possibly shift from native-like aggregation to conformational switch-initiated fibrillation as the pH is altered from neutral to acidic. The combined propensity-stability approach based on the initiation and termination points of beta(2)m aggregation not only assists us in deciphering the mechanism but also emphasizes the protagonistic roles of both terminal points in the overall aggregation process.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.4c06611}, author = {Tammara, Vaishnavi and Das, Atanu} }