Task 9: Normal Mode Analysis

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Revision as of 19:03, 9 August 2011 by Meier (talk | contribs) (Anisotropic Network Model web server)

There are several forces acting within a protein. Most of these forces have one or more equilibrium states. In reality the protein is flexible. That means, that the atoms of the system swing around these equilibrium states. These swinging around the equilibrium states can be approximated by the harmonic approximation. The forces can then be replaced by a less complex system of springs. With this model it is possible to calculate large motions of the protein by Normal Mode Analysis.

In opposite to Molecular Dynamics this is very fast and it is not a simulation it is a calculation of possible simple and large motions.

In this task we want to try several servers, which calculate normal mode analysis. A detailed description of the task can be found here. For most runs we used the structure 1J8U for our protein PAH. In the case of the all-atom NMA we used a smaller protein to test the server and this kind of approach.


The server WEBnm@ uses only the C-alpha atoms to calculate the normal modes. The calculations are performed using the Molecular Modelling Toolkit with the C-alpha force field.

The used input format is very easy (see below).

PAH WEbnma input field.png


The server offers different statistics and visualizations to the performed NMA calculation.

  • An atomic displacement analysis plots the displacement of each C-alpha atom, therefore one can inspect the parts of the protein, which are the most displaced for each mode. These plots are shown for PAH below.
  • Mode visualization and vector field analysis. The vector field representation of the modes shows the directions and (relative) amplitude of the displacements undergone by different parts of the protein as vectors. The visualization and the vector field analysis can be downloaded as vmd-files. But these files seem to be broken. The mode visualizations of PAH are shown below.

Plots of atomic displacement

Mode 7

PAH WEBNMA Mode7plot.png

Mode 8

PAH WEBNMA Mode8plot.png

Mode 9

PAH WEBNMA Mode9plot.png

Mode 10

PAH WEBNMA Mode10plot.png

Mode 11

PAH WEBNMA Mode11plot.png

Visualization of Normal Modes

Mode 7

PAH webnma Mode7.gif

Mode 8

PAH webnma Mode8.gif

Mode 9

PAH webnma Mode9.gif

Mode 10

PAH webnma Mode10.gif

Mode 11

PAH webnma Mode11.gif


ElNemo is a webserver using the Elastic Network Model to calculate the normal modes of proteins (Tirion, 1996; Tama et al., 2000; Delarue and Sanejouand, 2002). The Elastic Network is a network model of a protein. Usually the nodes in this network are the C-alpha atoms and the edges are the interactions within the protein simulated as springs. This approach sufficient to calculate the low-frequency normal modes of a protein.

The input form of elNemo seems to be not that simple at the first glance. The form is splitted in several subsections.

In the basic section you just have to define the protein structure by file or by copy-and-paste of the atom-section. Additionally one should define a job-title and specify an e-mail address. The e-mail address is useful, because the jobs need usually some time.

PAH elnemo basic input field.png

In the supplementary section you can define how many slow modes you want to see. Additionally you can define the number of structures calculated for each mode by defining the maximum and minimum amplitude and the step of amplitude.

PAH elnemo supplementary input field.png

The comparing section can be used to define a second conformation of the protein. elNemo calculates then the contribution of each normal mode to the second structure.

PAH elnemo comparing input field.png

The last section is for experts. Here you can define the granularity of the elastic network model. That means you can define the size of the substructures used for nodes and the threshold for interactions used as edges.

PAH elnemo expert input field.png

Compared to the default settings we just changed the cutoff for interactions to 15 Angstrom in the expert section.



Low Collectivity of Mode 4:


Visualization of Normal Modes

Mode 7

PAH ELNEMO Mode7 1.gif PAH ELNEMO Mode7 2.gif PAH ELNEMO Mode7 3.gif

Mode 8

PAH ELNEMO Mode8 1.gif PAH ELNEMO Mode8 2.gif PAH ELNEMO Mode8 3.gif

Mode 9

PAH ELNEMO Mode9 1.gif PAH ELNEMO Mode9 2.gif PAH ELNEMO Mode9 3.gif

Mode 10

PAH ELNEMO Mode10 1.gif PAH ELNEMO Mode10 2.gif PAH ELNEMO Mode10 3.gif

Mode 11

PAH ELNEMO Mode11 1.gif PAH ELNEMO Mode11 2.gif PAH ELNEMO Mode11 3.gif

Anisotropic Network Model web server

The Anisotropic Network Model web server is a web server for the calculation of the normal modes of proteins. This web server uses the Anisotropic network model (ANM) for the calculation of the normal modes (Bahar et al., 2000; Bahar et al., 2001). The ANM is a kind of Elastic Network. In this concrete case each node is the Cα atom of a residue and the edges are interactions between interacting nodes. Two nodes are interacting if their distance is below a certain threshold. The interactions are calculated by harmonic potentials. In contrast to the Gaussian Network Model the orientation of each interaction is considered in the calculation of the normal modes.

The input form of the server is very simple. Besides the definition of the used initial protein structure, one just has to/can define the cutoff distance for interactions and a distance weight. The distance weight adjusts the correlation between calculated and experimental b-factors.

PAH ANMA input.png

In our case we just adjusted the weight factor to 4.


Visualization of Normal Modes

Mode 1

PAH ANMA Mode1.gif

Mode 2

PAH ANMA Mode2.gif

Mode 3

PAH ANMA Mode3.gif

Mode 4

PAH ANMA Mode4.gif

Mode 5

PAH ANMA Mode5.gif

oGNM – Gaussian network model


All-atom NMA using Gromacs on the NOMAD-Ref server