Research Topics - Steered/Interactive Molecular Dynamics

Knowledge of the mechanism of association, dissociation and unfolding of macromolecules is important for many biological processes. Among the examples are the binding and dissociation of substrates of enzyme reactions, the recognition of ligands by their receptors or the elastic resopnse of mechanical proteins. In order to study such processes external forces can be applied reducing energy barriers and therefore increasing the probability of unlikely events on the time scale of molecular dynamics. This approach has the advantage that it corresponds closely to micromanipulation through atomic force microscopy or optical tweezers. The external force techniques can be applied to study many processes, including dissociation of avidin-biotin complex, dissociation of retinal from bacteriorhodopsin, stretching of titin, etc. The molecular dynamics program NAMD, developed in the group, is capable of performing several different kinds of SMD, including rotation or translation of one or more atoms. The group's molecular graphics program VMD provides a powerful means of visualizing these simulations, and through the Interactive Molecular Dynamics (IMD) interface can even allow SMD simulations to be performed in real time.

Molecular Motor Scooting along DNA

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made with VMD
movie ( 2.5MB )

DNA with its famous double helix structure stores the genetic information of all life forms known. In order that this information is read, the double helix needs to be first unwound and separated into single helices or strands. This is achieved by cellular motor proteins called helicases that operate on already separated DNA strands. The helicases specialize in unwinding and separating the DNA double helix by scooting along one of DNA's single strands against the point where the two strands merge into the double helix; pushing against this point unwinds and separates the double helix further. The helicases are driven by energy stored in molecules of ATP which bind to the protein and get released in their so-called hydrolyzed, lower energy, form. Based on atomic resolution structures, researchers have studied now one of the smallest helicases known, PcrA, from the electronic to the functional level carrying out quantum mechanical/molecular mechanical simulations (as described in a first publication), as well as a combination of classical molecular dynamics simulation, using NAMD, and stochastic modeling calculations (described in a second publication). This resulted in an overall explanation of how ATP's hydrolysis powers helicase activity which has been reported in a third publication. The researchers discovered that PcrA moves with two "hands" along single stranded DNA; when ATP binds, one "hand" moves along the DNA; when ADP and Pi (the hydrolysis products of ATP) unbind, the other "hand" moves; through a molecular "trick" both "hands" move in the same direction. Amazingly, the hand movement arises mainly from an increase in random mobility of the hands. i.e., is not enforced. Physicists refer to the underlying mechanism as a ratchet mechanism that was indeed long suspected to drive molecular motors. Interestingly, the helicase motor is very closely related to a wide class of other biological motors, for example the FoF1-ATP synthase (see Mar 2004 and Nov 2004 highlights). For more information visit our helicase research website.

All Spotlights


Onset of anthrax toxin pore formation. Mu Gao and Klaus Schulten. Biophysical Journal, 90:3267-3279, 2006.

What makes an aquaporin a glycerol channel: A comparative study of AqpZ and GlpF. Yi Wang, Klaus Schulten, and Emad Tajkhorshid. Structure, 13:1107-1118, 2005.

In search of the hair-cell gating spring: Elastic properties of ankyrin and cadherin repeats. Marcos Sotomayor, David P. Corey, and Klaus Schulten. Structure, 13:669-682, 2005.

Calculating potentials of mean force from steered molecular dynamics simulations. Sanghyun Park and Klaus Schulten. Journal of Chemical Physics, 120:5946-5961, 2004.

Insights into the molecular mechanism of rotation in the Fo sector of ATP synthase. Aleksij Aksimentiev, Ilya A. Balabin, Robert H. Fillingame, and Klaus Schulten. Biophysical Journal, 86:1332-1344, 2004.

Mechanisms of selectivity in channels and enzymes studied with interactive molecular dynamics. Paul Grayson, Emad Tajkhorshid, and Klaus Schulten. Biophysical Journal, 85:36-48, 2003.

Identifying unfolding intermediates of FN-III10 by steered molecular dynamics. Mu Gao, David Craig, Viola Vogel, and Klaus Schulten. Journal of Molecular Biology, 323:939-950, 2002.

Structural determinants of MscL gating studied by molecular dynamics simulations. Justin Gullingsrud, Dorina Kosztin, and Klaus Schulten. Biophysical Journal, 80:2074-2081, 2001.

Unfolding of titin immunoglobulin domains by steered molecular dynamics simulation. Hui Lu, Barry Isralewitz, André Krammer, Viola Vogel, and Klaus Schulten. Biophysical Journal, 75:662-671, 1998.

Molecular dynamics study of unbinding of the avidin-biotin complex. Sergei Izrailev, Sergey Stepaniants, Manel Balsera, Yoshi Oono, and Klaus Schulten. Biophysical Journal, 72:1568-1581, 1997.