Structural dynamics of full-length retroviral integrase: a molecular dynamics analysis

Influence of Cataract Causing Mutations on αA-Crystallin: A Computational Approach

The αA-crystallin protein plays a vital role in maintaining the refractive index and transparency of the eye lens. Significant clinical studies have emerged as the αA-crystallin is prone to aggregation, resulting in the formation of cataracts with varied etiologies due to mutations. This work aims to comprehend the structural and functional role of cataract-causing mutations in αA-crystallin, particularly at N-Terminal and α-Crystallin Domains, using in-silico approaches including molecular dynamics simulation. About 19 mutants of αA-crystallin along with native structure were simulated for 100 ns and the post-simulations analyses reveal pronounced dynamics of αA-crystallin due to the enhanced structure flexibility as its native compactness was lost and is witnessed mainly by the mutants R12L, R21L, R21Q, R54L, R65Q, R116C and R116H. It is observed that αA-crystallin discloses the NTD motions as the dominant one and the same was endorsed by the linear variation between Rg and the center-of-mass of αA-crystallin. Interestingly, such enhanced dynamics of αA-crystallin mutants associated with the structure flexibility is internally modulated by the dynamic exchange of secondary structure elements β-sheets and coils (R2 = 0.619) during simulation. Besides, the observed pronounced dynamics of dimer interface region (β3-L6-β4 segment) of ACD along with CTD dynamics also gains importance. Particularly, the highly dynamic mutants are also characterized by enhanced non-covalent and hydrophobic interactions which renders detrimental effects towards its stability, and favours possible protein unfolding mechanisms. Overall, this study highlights the mutation-mediated structural distortions in αA-crystallin and demands the need for further potential development of inhibitors against cataract formation.

The conformational feasibility for the formation of reaching dimer in ASV and HIV integrase: a molecular dynamics study

Retroviral integrases are reported to form alternate dimer assemblies like the core-core dimer and reaching dimer. The core-core dimer is stabilized predominantly by an extensive interface between two catalytic core domains. The reaching dimer is stabilized by N-terminal domains that reach to form intermolecular interfaces with the other subunit's core and C-terminal domains (CTD), as well as CTD-CTD interactions. In this study, molecular dynamics (MD), Brownian dynamics (BD) simulations, and free energy analyses, were performed to elucidate determinants for the stability of the reaching dimer forms of full-length Avian Sarcoma Virus (ASV) and Human Immunodeficiency Virus (HIV) IN, and to examine the role of the C-tails (the last ~16-18 residues at the C-termini) in their structural dynamics. The dynamics of an HIV reaching dimer derived from small angle X-ray scattering and protein crosslinking data, was compared with the dynamics of a core-core dimer model derived from combining the crystal structures of two-domain fragments. The results showed that the core domains in the ASV reaching dimer express free dynamics, whereas those in the HIV reaching dimer are highly stable. BD simulations suggest a higher rate of association for the HIV core-core dimer than the reaching dimer. The predicted stability of these dimers was therefore ranked in the following order: ASV reaching dimer < HIV reaching dimer < composite core-core dimer. Analyses of MD trajectories have suggested residues that are critical for intermolecular contacts in each reaching dimer. Tests of these predictions and insights gained from these analyses could reveal a potential pathway for the association and dissociation of full-length IN multimers.

Insights into the structural dynamics of Liver kinase B1 (LKB1) by the binding of STe20 Related Adapterα (STRADα) and Mouse protein 25α (MO25α) co-activators

LKB1, the tumour suppressor, is found mutated in Peutz-Jeghers syndrome (PJS). The LKB1 is a serine-threonine kinase protein that is allosterically activated by the binding of STRADα and MO25α without phosphorylating the Thr212 present at activation loop. The present study aims to highlight the structural dynamics and complexation mechanism during the allosteric activation of LKB1 by these co-activators using molecular dynamics simulations. The all atom simulations performed on the complexes of LKB1 with ATP, STRADα, and MO25α for a period of 30 ns reveal that binding of STRADα and MO25α significantly stabilizes the highly flexible regions of LKB1 such as ATP binding region (β1-β2 loop), catalytic & activation loop segments and αG helix. Also, binding of STRADα and MO25α to LKB1 promotes coordinated motion between N- and C-lobes along with the catalytic & activation loops by forming H-bonds between LKB1 and co-activators, which further facilitate to establish the conserved attributes of active LKB1 such as (i) formation of salt bridge between Lys78 and Glu98, (ii) formation of stable hydrophobic R- and C-spines, and (iii) interaction between both catalytic and activation loops. Especially, the residues of LKB1 interacting with STRADα (Arg74, Glu342) and MO25α (Glu165, Pro203 and Phe204) are observed to play a significant role in stabilizing the (LKB1-ATP)-(STRADα-ATP)-MO25α complex. Overall, the present work highlighting the structural dynamics of LKB1 by the binding of allosteric co-activators is expected to provide a basic understanding on drug design specific to PJS syndrome.

Structural dynamics of native and V260E mutant C-terminal domain of HIV-1 integrase

The C-terminal domain (CTD) of HIV-1 integrase is a five stranded β-barrel resembling an SH3 fold. Mutational studies on isolated CTD and full-length IN have reported V260E mutant as either homo-dimerization defective or affecting the stability and folding of CTD. In this study, molecular dynamics simulation techniques were used to unveil the effect of V260E mutation on isolated CTD monomer and dimer. Both monomeric and dimeric forms of wild type and V260E mutant are highly stable during the simulated period. However, the stabilizing π-stacking interaction between Trp243 and Trp243' at the dimer interface is highly disturbed in CTD-V260E (>6 Å apart). The loss in entropy for dimerization is -30 and -25 kcal/mol for CTD-wt and CTD-V260E respectively signifying a weak hydrophobic interaction and its perturbation in CTD-V260E. The mutant Glu260 exhibits strong attraction/repulsion with all the basic/acidic residues of CTD. In addition to this, the dynamics of CTD-wild type and V260E monomers at 498 K was analyzed to elucidate the effect of V260E mutation on CTD folding. Increase in SASA and reduction in the number of contacts in CTD-V260E during simulation highlights the instability caused by the mutation. In general, V260E mutation affects both multimerization and protein folding with a pronounced effect on protein folding rather than multimerization. This study emphasizes the importance of the hydrophobic nature and SH3 fold of CTD in proper functioning of HIV integrase and perturbing this nature would be a rational approach toward designing more selective and potent allosteric anti-HIV inhibitors.

Computational design of a full-length model of HIV-1 integrase: modeling of new inhibitors and comparison of their calculated binding energies with those previously studied

A full-length model of integrase (IN) of the human immunodeficiency virus type 1 (HIV-1) was constructed based on the distinctly resolved X-ray crystal structures of its three domains, named N-terminal, catalytic core and C-terminal. Thirty-one already known inhibitors with varieties of structural differences as well as nine newly tested ones were docked into the catalytic core. The molecular dynamic (MD) and binding properties of these complexes were obtained by MD calculations. The binding energies calculated by molecular mechanic/Poisson Boltzmann solvation area were significantly correlationed with available IC50. Four inhibitors including two newly designed were also docked into the full-length model and their MD behaviors and binding properties were calculated. It was found that one of the newly designed compounds forms a better complex with HIV-1 IN compared to the rest including raltegravir. MD calculations were performed with AMBER suite of programs using ff99SB force field for the proteins and the general Amber force field for the ligands. In conclusion, the results have produced a promising standpoint not only in the construction of the full-length model but also in development of new drugs against it. However, the role of multimer formation and the involvement of DNAs, and their subsequent effect on the complexation and inhibition, are required to arrive at a conclusive decision.