Passage
The tumor suppressor p53 is a homotetrameric protein with an N-terminal transactivation domain (TAD) , a proline-rich domain, a DNA-binding domain (DBD) , a tetramerization domain (TD) , and a C-terminal regulatory domain (REG) on each subunit (Figure 1) .
Figure 1 Organization of the p53 domains (1-393 amino acids) Human double minute 2 (Hdm2) is a lysine-specific ubiquitin protein ligase that can change the half-life of some proteins, including p53, by signaling for their proteolytic cleavage. Under normal circumstances, Hdm2 binds p53 at the AD1 region within the TAD and attaches ubiquitin to a lysine residue. However, errors in DNA replication induce the phosphorylation of residue T18 on p53, which inhibits p53's association with Hdm2. The overexpression of Hdm2 has been correlated with the downregulation of tumor suppressor p53 in certain types of cancers. Changes in the NMR chemical shift (ppm) of amino acids in the AD1 region shown in Figure 2 provide evidence for the formation of a p53-Hdm2 complex.
Figure 2 ¹H NMR spectrum of the AD1 region in ¹⁵N-labeled p53 during G₀ and G₂ phases of the cell cycleHdm2 also binds to Nedd8 ultimate buster 1 (NUB1) , which enhances signaling for the degradation of Nedd8 proteins. Preliminary data suggest that Hdm2 interacts differently with wild-type NUB1 (WTNUB1) than with mutant K159RNUB1. To assess the effect of Hdm2 on NUB1 and p53, the half-lives of p53 and Nedd8 protein variants were compared in cells that overexpress Hdm2 (Figure 3) .
Figure 3 Half-lives of p53, phosphorylated p53 (p53-PO₄) , and Nedd-8 proteins in cells with wild-type or mutant NUB1 over time
Adapted from Ferreon JC, Lee CW, Arai M, Martinez-yamout MA, Dyson HJ, Wright PE. Cooperative regulation of p53 by modulation of ternary complex formation with CBP/p300 and HDM2. Proc Natl Acad Sci USA. 2009;106(16) :6591-6.
-Which statement best explains the relationship between Hdm2 and Nedd8 protein concentration?

Question

Passage
The tumor suppressor p53 is a homotetrameric protein with an N-terminal transactivation domain (TAD) , a proline-rich domain, a DNA-binding domain (DBD) , a tetramerization domain (TD) , and a C-terminal regulatory domain (REG) on each subunit (Figure 1) .

Figure 1 Organization of the p53 domains (1-393 amino acids) Human double minute 2 (Hdm2) is a lysine-specific ubiquitin protein ligase that can change the half-life of some proteins, including p53, by signaling for their proteolytic cleavage. Under normal circumstances, Hdm2 binds p53 at the AD1 region within the TAD and attaches ubiquitin to a lysine residue. However, errors in DNA replication induce the phosphorylation of residue T18 on p53, which inhibits p53's association with Hdm2. The overexpression of Hdm2 has been correlated with the downregulation of tumor suppressor p53 in certain types of cancers. Changes in the NMR chemical shift (ppm) of amino acids in the AD1 region shown in Figure 2 provide evidence for the formation of a p53-Hdm2 complex.

Figure 2 ¹H NMR spectrum of the AD1 region in ¹⁵N-labeled p53 during G₀ and G₂ phases of the cell cycleHdm2 also binds to Nedd8 ultimate buster 1 (NUB1) , which enhances signaling for the degradation of Nedd8 proteins. Preliminary data suggest that Hdm2 interacts differently with wild-type NUB1 (WTNUB1) than with mutant K159RNUB1. To assess the effect of Hdm2 on NUB1 and p53, the half-lives of p53 and Nedd8 protein variants were compared in cells that overexpress Hdm2 (Figure 3) .

Figure 3 Half-lives of p53, phosphorylated p53 (p53-PO₄) , and Nedd-8 proteins in cells with wild-type or mutant NUB1 over time
Adapted from Ferreon JC, Lee CW, Arai M, Martinez-yamout MA, Dyson HJ, Wright PE. Cooperative regulation of p53 by modulation of ternary complex formation with CBP/p300 and HDM2. Proc Natl Acad Sci USA. 2009;106(16) :6591-6.
-Which statement best explains the relationship between Hdm2 and Nedd8 protein concentration?

Quizplus · Accepted Answer

11ecba2d_0e04_9ad2_a3bf_730d47b96c95_MD0008_00 Positive regulators bind reversibly at positions outside the active site and enhance the activity of their target protein. Hdm2 regulates protein activity by attaching a ubiquitin molecule to its target protein. According to the passage, NUB1 proteins are targets for Hdm2 regulation. The function of wild-type NUB1 (WTNUB1) is to enhance signaling for the degradation of Nedd8 proteins, so its presence reduces the half-life of Nedd8. Based on the data shown in Figure 3, Hdm2 acts as a positive regulator of NUB1 proteins: in the presence of Hdm2, WTNUB1 induces continuous degradation of Nedd8. However, K159R mutants do not induce the degradation of Nedd8 proteins. This reduction in function implies that the K159R mutation prevents Hdm2 from binding to NUB1. As a result, K159R mutants do not actively reduce the half-life of Nedd8 proteins even though Hdm2 proteins are present. Therefore, the degradation of Nedd8 proteins is more efficient when NUB1 is bound by Hdm2. (Choice A) Hdm2 activity increases Nedd8 degradation; therefore, Nedd8 protein concentration is inversely proportional to Hdm2 activity. (Choice C) Nedd8 protein concentration decreases when WTNUB1 is bound to Hdm2. (Choice D) Hdm2 binding does not signal for the degradation of NUB1 proteins. Instead, Nedd8 protein levels depend on NUB1 being activated by Hdm2. Educational objective: Positive regulators bind reversibly at positions outside the active site and enhance the activity of their target proteins.

Passage the Tumor Suppressor P53 Is a Homotetrameric Protein with an an N-Terminal