The First Super-Microsecond Molecular Dynamics Simulation of a Protein-Ligand Complex: MUP/IBM

Lead Research Organisation: University of Nottingham
Department Name: Sch of Pharmacy

Abstract

One of the defining features of life is motion, and it is the ability of biological molecules like proteins to move and change shape - to function as 'molecular machines' - that underpins this. Most experimental methods to study biological molecules at the atomic scale - for example X-ray crystallography and NMR spectroscopy - can only provide static 'snapshots' of their structure. But starting with this information, computer simulation methods, particularly molecular dynamics simulations, allow us to visualise the dynamical motions of proteins and other biological molecules, enabling us to understand how these molecules 'work'. The problem is that these simulations require enormous amounts of computer power. Until recently, it was only possible to follow the motions of biological molecules for very short periods of time - a few billionths of a second. But the new UK supercomputer HECToR has the power to increase this to the microsecond (1 millionth of a second) timescale. This still sounds like a very small period of time, but actually within a microsecond a lot of important biological processes can occur. This project will study the dynamics of a small protein from mice that acts as a molecular sponge, soaking up molecules of the mouse's pheromones. This may sound quite esoteric but is actually a well-established 'testbed system' for understanding important processes like drugs binding to their targets, and so will provide very useful information to help with drug design and development.

Publications

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Description The mouse major urinary protein (MUP) has proved to be an intriguing test bed for detailed studies on proteinligand

recognition. NMR, calorimetric, and modeling investigations have revealed that the thermodynamics of ligand binding

involve a complex interplay between competing enthalpic and entropic terms. We performed six independent, 1.2 ms molecular-

dynamics simulations on MUP-three replicates on the apo-protein, and three on the complex with the pheromone isobutylmethoxypyrazine.

Our findings provide the most comprehensive picture to date of the structure and dynamics of MUP, and how

they are modulated by ligand binding. The mechanical pathways by which amino acid side chains can transmit information

regarding ligand binding to surface loops and either increase or decrease their flexibility (entropy-entropy compensation) are

identified. Dewetting of the highly hydrophobic binding cavity is confirmed, and the results reveal an aspect of ligand binding

that was not observed in earlier, shorter simulations: bound ligand retains extensive rotational freedom. Both of these features

have significant implications for interpretations of the entropic component of binding. More generally, these simulations test

the ability of current molecular simulation methods to produce a reliable and reproducible picture of protein dynamics on the

microsecond timescale.
Sectors Pharmaceuticals and Medical Biotechnology