Question

α-Helices are often membrane spanning structures, that are typically 18-21 amino acids long. What would be the effect of a mutation that results in the replacement of 4 valines in the middle of this helix, by 2 lysines and a 2 histidines? Use figure 5.14 (inserted below) to answer this question.

Noraside in hydrophobic side chain group HON CH CHCH CH CH, CH CM CH HC-01 HUN MN- WN H Glor Maine TALAJ Weline Valor Leucine O hole ale or ON CHE NH OL CH сн. HN Hy Hi HN Metho Motor Phenylalanine hor" Try pa Proline Pro Polarite charaphil CH OH DI ON CH, OU CM HN There (The Op o Apare AN tெe Chically charged side chain Buskelly charged Additively charged

Answer 1

as it has been mentioned that the alpha helix has seen to be the membrane spanning structure with the 18-20 amino acid residues long. Then, if the middle range of the amino acid residues has been altered in such a way that the positively charged lysine and histidine has been added then the membrane spanning ability of the alpha helix will have an obstruction which can be overuled by formation of the core through this amino acid resiues.

However, if the middle range of the alpha helix will be of the positively charged amino acid residues then that particular nature of the protein will convert to the hydrophobic and thus there can be the hydrophobic interaction between the lipid tails of the phospholipids involved in the cell membrane formation. and also, there can be the possibility that the repulsion for the particular amino acid can be seen in this particular region of the cell membrane.

This can be neglected if the folding of the alpha helix has been taken place in such a way that this molecules has been transferred into the backbone of the structure where all the positively charged amino acids are involved and thus that will form the core part of the structure.