|Mutation Codon||Leu -> Arg|
|Mutation Triplet||CTT -> CGT|
First of all, we explored the amino acid properties and compared them for the original and the mutated amino acid. Therefore we created the possible effect that the mutation could have on the protein.
|aliphatic, hydrophobic, neutral||positive charged, polar, hydrophilic||Leucine is smaller and without a positive charge. Therefore, Arg is too big for the position of Leu, therefore, the change of Leu with Arg has to cause changes in the 3D structure of the protein. Furthermore, Leu is a hydrophobic amino acid, whereas Arg is hydrophilic. This is the complete contrary and therefore we suggest, that the protein will not function any longer.|
Visualisation of the Mutation
In the next step, we created the visualization of the muation with PyMol. Therefore we created a picture for the original amino acid, for the new mutated amino acid and finally for both together in one picture whereas the mutation is white colored. The following pictures display that the mutated amino acid Arginine has a longer chain than Leucine. Contrary Leucine comes to a fork at the end of its rest. This shows that the amino acids have some structural differences that are not drastical, but can be essential.
|picture original aa||picture mutated aa||combined picture|
Subsitution Matrices Values
Afterwards, we looked at the values of the substitution matrices PAM1, PAM250 and BLOSSUM62. Therefore we looked detailed at the three values: the value for accoding amino acid substitution, the most frequent value for the substitution of the examined amino acid and the rarest substitution.
In this case, the substitution of Leucine to Arginine has very low values that are near the values for the rarest subsitution for PAM1 and PAM250. Furthermore, the value for the most frequent substitution differs also a lot from the value for this certain mutation for both PAMs. Contrary for BLOSUM62 the value for the amino acid subsitution Leucine to Arginine is average. This means the most frequent subsitution value is as far as the rarerest subsitution from the the underlying value. The difference between the two PAMs and BLOSUM62 can be ascribed to the different preparations of these two kind of substitutions matrices. The PAM-matrices is an evolutionary model whereas BLOSUM is based on protein famalies. Therefore probably this mutation is evolutionary not that unlikely whereas within a protein family it is unusual. Therefore, according to PAM1 and PAM250 a mutation at this position will almost certainly cause structural changes which can affect functional changes. The value from BLOSSUM62 is not realy significant and therefore we are not able to determine effects on the protein.
|PAM 1||Pam 250||BLOSOUM 62|
|value aa||most frequent substitution||rarest substitution||value aa||most frequent substitution||rarest substitution||value aa||most frequent substitution||rarest substitution|
|1||22 (Ile)||0 (Asp, Cys)||4||20 (Met)||2 (Cys)||-2||0 (Phe)||-4 (Asp, Gly)|
Besides, we looked additional at the position specific scoring matrix (PSSM) for ouer sequence. In contrast to PAM and BLOSOUM, the PSSM contains a specific substitution rate for each position in the sequence. Therefore, the PSSM is more position specific than PAM or BLOSOUM. We extracted the substitution value for the underlying mutation, the value for the most frequent substitution and the rarest substitution.
In this case the substitution rate for Isoleucine to Valine acid at this position is very low and near the value for the rarest substitution. This means this substitution at this position is likely very uncommon which indicates that this substitution has bad effects as a consequence. Therefore, we conclude that this mutation will probably cause protein structure changes as well as functional changes.
|value aa||most frequent substitution||rarest substitution|
Conservation Analysis with Multiple Alignments
As a next step we created a multiple alignment which contains the HEXA sequence and 9 other mammalian homologous sequences from uniprot. Afterwards we looked at the position of the different mutations and looked at the conservation level on this position. The regarded mutation is presented by the second colored column. Here we can see, that the most other mammalians have on this Position a Leucine. Only three mammalians differ and have on this position an Isoleucine. Therefore, the mutation on this position has probably a structural and functional change as a result.
Secondary Structure Mutation Analysis
As a next step we compared the different results of the secondary structure prediction tools JPred and PsiPred. Afterwards we can examine in which secondary structure element and at which therein the mutation takes place. This can give an overview of how drastical the mutation can be. In this case both tools agree and predict at the position of the mutation the end of a sheet. This means that there is almost certainly the end of the beta sheet. This has a result, that the mutation at this position would not destroy or split the whole beta-sheet. It will probably only change the end of the sheet, but it can also cause a change of the the following secondary structure. This can also have functional loose as a consequence, but we think that this is unlikely here.
JPred: CCHHHHHHHHHHHHHCCCCCCCEEEEEEEEEECCCEEEEECCCEEEEECCCCCCC... PsiPred: CHHHHHHHHHHHHHHHCCCCCCCCCCCCEEEECCCEEEEECCCEEEEECCCCCCC...
Comparison with the real Structure:
Afterwards we also visualize the position of the muation (red) in the real 3D-structure of PDB and compare it with the predicted secondary structure. The visualisation can therefore like above the predicted secondary structure display if the mutation is in a secondary structure element or in some other regions.
Here in this case the mutationposition agree with the position of the predicted secondary structure and is at the end of a beta sheet. Like explained above this means a mutation will probably not destroy the whole beta sheet what could hase as a result that the structural change is not as drastical. Otherwise it can cause a change of the further secondary structure element which can has a functional loose as a consequence.
Next, we looked at the result of the SNAP prediction. For this prediction we took the amino acid of the certain position and checked every possible amino acid mutation. Afterwards we extract the result for Arginine which is the real mutation in this case. SNAP has a result that the exhange from Leucine to Arginine at this position is not neutral with a comparitive high accuracy. This means that this certain mutation on this position cause very likely structural and functional changes of the protein.
|Substitution||Prediction||Reliability Index||Expected Accuracy|
A detailed list of all possible substitutions can be found [here]
Next, we used SIFT Prediction which displays if a mutation is neutral or not. Therefore, it first shows a row which contains a score for the particular mutationposition to a certain amino acid. The amino acid which are not tolerated at this position are colored red. Besides, it also constructs a table which lists the amino acids that are predicted as tolerated and not-tolerated.
In this case, there are only three substitutions that are tolerated: Valine, Isoleucine and Leucine. The substitution to Arginine is not-tolerated at this position. This means that this mutation at this position is probably not neutral and will cause probably structural and function changes of the protein.
Each entry contains the score at a particular position (row) for an amino acid substitution (column). Substitutions predicted to be intolerant are highlighted in red.
Threshold for intolerance is 0.05.
Amino acid color code: nonpolar, uncharged polar, basic, acidic.
Capital letters indicate amino acids appearing in the alignment, lower case letters result from prediction.
Finally, we also regarded the PolyPhen2 prediction for this muation. This prediction visualizes have strongly demaging the mutation probably will be. Therefore it gives the result for two possible cases: HumDiv and HumVar. HumDiv is a prefered model for evaluation rare allels, dense mapping of regions identified by genome-wide assiociation studies and analysis of neutral selection. In contrast, HumVar is a prefered model for diagnostic of Mendelian diseases which require distinguishing mutations with drastic effects from all remaining human variations including abundant mildly deleterious allels. We decided to look at both possible models, which are agrees in the most cases.
In this case both models predict that the mutation is probably damaging. This means that the mutation is not neutral and will probably destroy the structure and the function of the protein.