Phosphorylation can affect the structure or function of a protein in which of th
ID: 91413 • Letter: P
Question
Phosphorylation can affect the structure or function of a protein in which of the following ways? I. Charge attraction between the phosphate group and positively charged amino acids causes a conformational change in the protein. II. Charge repulsion between the phosphate group and negatively charged amino acids causes a conformational change in the protein. III. The phosphate group creates a binding site for another protein. a. I b. III c. I and II d. I, II, and III Which of the following hypotheses provides the most likely explanation for how phosphorylation of Rb causes its dissociation from E2F? a. Phosphorylation of Rb causes E2F to change conformation so that it dissociates from Rb. b. Phosphorylation of Rb causes it to undergo a conformational change that blocks the E2F binding site. c. Phosphorylation of Rb inactivates the Rb binding site for Cdk. d. Phosphorylation of Rb leads to a charge repulsion between the phosphate group and a positively charged pocket on E2F.Explanation / Answer
C.
Correct answer is d. I, II and III.
Phosphate group bound to the protein carries two negative charges. This can cause major conformational changes in the protein either by attracting a cluster of positively charges R groups of aminoacids or by repelling a cluster of negatively charges R groups of aminoacids.
Tyrosine residues in the cytoplasmic side of receptor tyrosine kinases (RTK) undergo phosphorylation. Without this phosphorylation, -SH2 domain containing proteins in cytoplasm cannot bind to RTK. Phosphorylation creates binding sites for SH2 domain containing proteins on RTKs.
D.
Correct answer is B
When phosphorylated at S608/S612 and T356/T373 residues, Rb undergoes conformational change. This inhibits the association between E2F transactivation domain and Rb.
If you are interseted in reading further regarding the confirmational changes in Rb, you may refer to the following paper.
Burke, J.R., Deshong, A.J., Pelton, J.G. and Rubin, S.M., 2010. Phosphorylation-induced conformational changes in the retinoblastoma protein inhibit E2F transactivation domain binding. Journal of Biological Chemistry, 285(21), pp.16286-16293.