Question

1. Ricky always appears dehydrated. Ricky goes to the hospital to have his blood analyzed to determine a possible cause. Ricky is told that one of his proteins responsible for uptalking water into the cell is defective (not in its normal final folded conformation) due to a mutation. What type of protein is responsible for allowing water to enter the cell? What type of folding defect would disrupt water from flowing through?
2. Grp170a is a chaperone protein constitutively expressed, while grp170b is inducible. Which protein do you think will be present at high levels in response to extreme heat stress (leading proteins to unfold). Explain your answer.

Answer 1

* Aquaporins are member of an intristic protein family and are responsible for allowing water to enter into the cell.They have 6 alpha domains integrated in plasma membrane of cell with both carboxyl and amino terminals on the cytoplasmic side. They form channels/pores for water to transport.

* Aquaporins have a conserved structure. some mutations affect the stability of the structural complex of this protein thus cause disrupted water flow to the cells. Each monomer of aquaporin has 6 alpha helix and two recentry loops which both form a half spanning helix which span the membrane.The 8 helices together form a right handed helix bundle with a pore in its centre.correct folding depends on helix–helix interactions, which are determined by the amino acid sequence of interacting helices. So due to mutation tight helix helix contact may reduce the pore size thus allowing less water to flow through it.

* Grp170b will be present at high level in response to extreme heat loss as it is an inducible protein. Grp170a is a chaperon protein which is responsible for protein folding but it needs to be induced and can't be expressed alone even if present in high levels. So Grp170b protein will induce it to refold the proteins during extreme heat stress . For this, Grp170b protein level will increase.