Tags

Type your tag names separated by a space and hit enter

Atomic resolution mechanism of ligand binding to a solvent inaccessible cavity in T4 lysozyme.
PLoS Comput Biol 2018; 14(5):e1006180PC

Abstract

Ligand binding sites in proteins are often localized to deeply buried cavities, inaccessible to bulk solvent. Yet, in many cases binding of cognate ligands occurs rapidly. An intriguing system is presented by the L99A cavity mutant of T4 Lysozyme (T4L L99A) that rapidly binds benzene (~106 M-1s-1). Although the protein has long served as a model system for protein thermodynamics and crystal structures of both free and benzene-bound T4L L99A are available, the kinetic pathways by which benzene reaches its solvent-inaccessible binding cavity remain elusive. The current work, using extensive molecular dynamics simulation, achieves this by capturing the complete process of spontaneous recognition of benzene by T4L L99A at atomistic resolution. A series of multi-microsecond unbiased molecular dynamics simulation trajectories unequivocally reveal how benzene, starting in bulk solvent, diffuses to the protein and spontaneously reaches the solvent inaccessible cavity of T4L L99A. The simulated and high-resolution X-ray derived bound structures are in excellent agreement. A robust four-state Markov model, developed using cumulative 60 μs trajectories, identifies and quantifies multiple ligand binding pathways with low activation barriers. Interestingly, none of these identified binding pathways required large conformational changes for ligand access to the buried cavity. Rather, these involve transient but crucial opening of a channel to the cavity via subtle displacements in the positions of key helices (helix4/helix6, helix7/helix9) leading to rapid binding. Free energy simulations further elucidate that these channel-opening events would have been unfavorable in wild type T4L. Taken together and via integrating with results from experiments, these simulations provide unprecedented mechanistic insights into the complete ligand recognition process in a buried cavity. By illustrating the power of subtle helix movements in opening up multiple pathways for ligand access, this work offers an alternate view of ligand recognition in a solvent-inaccessible cavity, contrary to the common perception of a single dominant pathway for ligand binding.

Authors+Show Affiliations

Tata Institute of Fundamental Research, Hyderabad, India.Tata Institute of Fundamental Research, Hyderabad, India.Tata Institute of Fundamental Research, Hyderabad, India.Departments of Molecular Genetics, Biochemistry and Chemistry, University of Toronto, Toronto, Ontario, Canada. Hospital for Sick Children Program in Molecular Medicine, Toronto, Ontario, Canada.Tata Institute of Fundamental Research, Hyderabad, India.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

29775455

Citation

Mondal, Jagannath, et al. "Atomic Resolution Mechanism of Ligand Binding to a Solvent Inaccessible Cavity in T4 Lysozyme." PLoS Computational Biology, vol. 14, no. 5, 2018, pp. e1006180.
Mondal J, Ahalawat N, Pandit S, et al. Atomic resolution mechanism of ligand binding to a solvent inaccessible cavity in T4 lysozyme. PLoS Comput Biol. 2018;14(5):e1006180.
Mondal, J., Ahalawat, N., Pandit, S., Kay, L. E., & Vallurupalli, P. (2018). Atomic resolution mechanism of ligand binding to a solvent inaccessible cavity in T4 lysozyme. PLoS Computational Biology, 14(5), pp. e1006180. doi:10.1371/journal.pcbi.1006180.
Mondal J, et al. Atomic Resolution Mechanism of Ligand Binding to a Solvent Inaccessible Cavity in T4 Lysozyme. PLoS Comput Biol. 2018;14(5):e1006180. PubMed PMID: 29775455.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Atomic resolution mechanism of ligand binding to a solvent inaccessible cavity in T4 lysozyme. AU - Mondal,Jagannath, AU - Ahalawat,Navjeet, AU - Pandit,Subhendu, AU - Kay,Lewis E, AU - Vallurupalli,Pramodh, Y1 - 2018/05/18/ PY - 2018/01/19/received PY - 2018/05/06/accepted PY - 2018/05/31/revised PY - 2018/5/19/pubmed PY - 2018/6/19/medline PY - 2018/5/19/entrez SP - e1006180 EP - e1006180 JF - PLoS computational biology JO - PLoS Comput. Biol. VL - 14 IS - 5 N2 - Ligand binding sites in proteins are often localized to deeply buried cavities, inaccessible to bulk solvent. Yet, in many cases binding of cognate ligands occurs rapidly. An intriguing system is presented by the L99A cavity mutant of T4 Lysozyme (T4L L99A) that rapidly binds benzene (~106 M-1s-1). Although the protein has long served as a model system for protein thermodynamics and crystal structures of both free and benzene-bound T4L L99A are available, the kinetic pathways by which benzene reaches its solvent-inaccessible binding cavity remain elusive. The current work, using extensive molecular dynamics simulation, achieves this by capturing the complete process of spontaneous recognition of benzene by T4L L99A at atomistic resolution. A series of multi-microsecond unbiased molecular dynamics simulation trajectories unequivocally reveal how benzene, starting in bulk solvent, diffuses to the protein and spontaneously reaches the solvent inaccessible cavity of T4L L99A. The simulated and high-resolution X-ray derived bound structures are in excellent agreement. A robust four-state Markov model, developed using cumulative 60 μs trajectories, identifies and quantifies multiple ligand binding pathways with low activation barriers. Interestingly, none of these identified binding pathways required large conformational changes for ligand access to the buried cavity. Rather, these involve transient but crucial opening of a channel to the cavity via subtle displacements in the positions of key helices (helix4/helix6, helix7/helix9) leading to rapid binding. Free energy simulations further elucidate that these channel-opening events would have been unfavorable in wild type T4L. Taken together and via integrating with results from experiments, these simulations provide unprecedented mechanistic insights into the complete ligand recognition process in a buried cavity. By illustrating the power of subtle helix movements in opening up multiple pathways for ligand access, this work offers an alternate view of ligand recognition in a solvent-inaccessible cavity, contrary to the common perception of a single dominant pathway for ligand binding. SN - 1553-7358 UR - https://www.unboundmedicine.com/medline/citation/29775455/Atomic_resolution_mechanism_of_ligand_binding_to_a_solvent_inaccessible_cavity_in_T4_lysozyme_ L2 - http://dx.plos.org/10.1371/journal.pcbi.1006180 DB - PRIME DP - Unbound Medicine ER -