Question

Using the hydropathy profile shown below (Y axis: hydropathy), researchers identified two significant stretches of hydrophobic aminoacid residues (highlighted in red). Name each one of them and explain their significance for the localization of this protein. (a) Human growth hormone receptor (type 1) N-terminus 200 400 500 C-terminus 1. Where do you expect the mRNA coding for human growth hormone receptor to be translated? 2. Which part of this protein will be recognized by the signal recognition particle (SRP)? 3. Do you expect to find the most N-terminal stretch of hydrophobic residues in the mature protein present at the plasma membrane? Why? 4. The translocation of trans-membrane proteins through the Sec61 translocon at the ER membrane requires energy. Where does it come from?

Answer 1

Hydropathy plot measures the degree of hydrophobicity or hydriphilicity of amino acids of a protein and it helps to characterize a protein and it helps to localize potential alpha helix membrane spanning segments in a polypeptide chain.

So here, the area or peak highlighted in red will be non polar residues which is an integral prorein spans once on the membrane.

1. The translation is likely to occur around the range of 270 - 290 residue number.

2. SRP is signal recognition particle, it can bind with the N-terminal hydrophobic signal sequence as well as with the ribosome (exactly P and E site) present in the cytosol. After binding, it will escorts into the SRP receptor.

3. Yes, after escorting the ribosome resumes translation and the No terminal signal sequence will be cleaved and the rest formed residues will be places on to the membrane in a mature alpha helix configuration as it us hydrophobic in nature.

4. The binding of SRP and SRP receptor, both need the hydrolysis of GTP independently. After that, the signal sequence will be cleaved by signal peptidase, it will release some energy. The energy needs for translocation will be fulfilled by this energy.

And further the amino acid residue will place on the membrane.

I hope you understand the concept well.

Thank you