Q125E

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Revision as of 13:30, 11 August 2011 by Demel (talk | contribs) (Structure-based Mutation Analysis)

Structure-based Mutation Analysis

Mapping onto crystal structure

Figure 1 shows the protein structure with highlighted amino acids. The mutation position is colored violet, the thiamine pyrophosphate binding sites are orange, and metal binding sites are yellow.

File:BCKDHA mut2.png
Figure 1: Structure of tyrosine on position 82 in the wildtype protein

Side chain properties

Figures 2 and 3 show the superposition of the mutated amino acid with the wildtype. The pictures showing the wildtype structure display the unmutated residue in bold and vice versa.


Figure 2: Structure of glutamineon position 125 in the wildtype protein
Figure 3: Structure of glutamic acid on position 125 in the mutated protein

Hydrogen Bonding network

Hydrogen bonds are interactions between an hydrogen atom and an electronegative atom. Electronegative atoms which often take part in hydrogen bonds are oxygen, nitrogen and fluorine (not present in amino acid side chains). They serve as a hydrogen bond acceptor, whereas a hydrogen bond donor is a electronegative atom bonded to a hydrogen atom. Hydrogen bonds are essential for the three-dimensional structures of proteins. They play a important role in the formation of helices and beta-sheets and cause proteins to fold into a specific structure.

Showing hydrogen bonds with Pymol: A -> find -> polar contacts -> within selection The respective amino acids were colored by element, s.t. oxygen is red, nitrogen is blue, hydrogen is white and sulfur is yellow.

The following figures show the hydrogen bonds between the wildtype residue and its environment compared to the formation of hydrogen bonds when the corresponding residue is mutated.


Figure 4: Hydrogen Bonds for glutamine on pos 125 in the wild type structure
Figure 5: Hydrogen Bonds for glutamic acid on pos 125 in the mutated type structure

The substitution from glutamine to glutamic acid changes the side chain properties completely. A NH2 group is substituted by a negatively charged oxygen. The NH2 which served in the wildtype structure as a hydrogen bond acceptor (see Figure 4) is not present any more, so the hydrogen bonding network changed for this substitution (compare Figure 4 and 5).

foldX Energy Comparison

We used the foldX tool to compare the energy of the wildtype protein and the mutated structure. The following table shows the calculated energy values as well as the percentage of difference, to compare the energy calculations with other tools:

Energy wildtype energy total energy of mutated protein difference
absolute 401.00 431.77 30.77
relative 100% 107% 7%

The total energy of the mutated structure is a little bit higher than the energy of the wildtype protein structure. As protein energies should be low for a stable protein, the increasing energy leads to the assumption that this mutation might be damaging for the protein structure.

minimise Energy Comparison

Next we used the minimise tool to compare the energy of the wildtype protein and the mutated structure. The following table shows the calculated energy values as well as the percentage of difference, to compare the energy calculations with other tools:

Energy wildtype energy total energy of mutated protein difference
absolute -2485.452755 -4080.989512 -1595.536757
relative 100% 60% 40%

The mutated structure has an energy that is much smaller than the wildtype

gromacs Energy comparison

The Gromacs energy comparison was conducted using the AMBER03 force field. The following table shows the calculated energies for the wildtype protein structure.

Energy Average Err.Est RMSD Tot-Drift (kJ/mol)
Bond 3072.83 2200 -nan -13100.2
Angle 3616.97 230 -nan -1295.57
Potential 2.67001e+07 2.6e+07 -nan -1.60382e+08

Here are the results for the mutated protein structure.

Energy Average Err.Est RMSD Tot-Drift (kJ/mol)
Bond 2519.85 1700 6351.32 -10027.5
Angle 3626.21 260 618.433 -1418.24
Potential 5.23e+06 5.2e+06 7.5e+07 -3.17e+07


As we want to compare the Gromacs energies with the other tools, we calculate the ratio of difference considering the potential energy:

Energy wildtype energy total energy of mutated protein difference
absolute 2.67001e+07 5.23e+06 --21470100
relative 100% 19% 81%

The calculated energy for the mutated structure is much smaller than for the wildtype structure.

Conclusion

return to Structure-based mutation analysis