Task 9 (MSUD)
For this task we have chosen 5 mutations from HGMD and dbSNP. 2 of them are neutral mutations which do not have functional changes over the protein structure. Following are the 5 mutations:
Selection of structure model
The following table shows an overview of all structures that are available for our protein:
Unfortunately all structures contain gaps that span positions 302-304 (corresponding to 347-349 in the reference sequence), so we cannot create a composite structure, that does not contain this gap. We chose 2BFF because it has the smallest gap, a good resolution and a low R-value. It is not resolved at physiological pH, but the only structure with pH 7.5 (1DTW) has a bad resolution. The RMSD between 2BFF and 1DTW is about 0.3, so the different pH does not lead to a different structure and therefore the low pH at that 2BFF was resolved should not be a problem.
Visualization of mutant structures
The mutagen tool of PyMOL was used to introduce mutations to the protein structure. Mutations and their neighboring residues are visualized and shown in following figures.
|Mutation||PDB||SD||total||energy||Backbone||Hbond||Sidechain||Hbond||Van der Waals|
Resulted structural models were compared to the structures calculated by SCWRL. By using alignment tool of PyMOL, we did not find any global deviation between the structures. Sequentially, structures produced by SCWRL have some residues missing. Following table shows the sequential difference.
|Mutation||RMSD(Å)||Missing residues in SCWRL|
In 3 mutant structures the mutation residues have different side-chain conformation between results of FoldX and SCWRL. The other 2 mutant structures do not show such difference.
The enegies of each Minimise run for the wild type and mutant structures are given in the following table. For the mutant structures there was only an output for structures calculated with FoldX. For input structures from SCWRL, Minimise gave no output (probably there was a problem with gaps).
A reduction in the energy can only be observed for C264W, and only for the second recursive run. All other energies increase slightly with every run, but are overall similar to each other.
- For the disease causing mutations (C264W and R346H), FoldX and SCWRL come to different results regarding the side chain conformation. This gives an indication, that the substituted amino acids do not fit into the local environment compared to the wild type structure. So they change the structure of the protein and hence can alter its function.
- The tryptophane that replaces a cysteine in C264W reaches into an ion binding site and so might interfere with binding of that ion, resulting in inhibition of enzymatic activity.
- We did not observe any minimization when running Minimise on the WT and mutant structures (except for C264W), the energy rather stagnated around a value of about -17000. Probably the structures are already in an energy minimum and can not be minimized any more, which does not mean that the mutant structures keep the functionality of the wild type.