Your friend is intrigued by Cdks and purifies Cdk from the daisy plant. She is a
ID: 70629 • Letter: Y
Question
Your friend is intrigued by Cdks and purifies Cdk from the daisy plant. She is able to determine the sequence of 18 amino acids from the daisy protein. Using these data, she aligns the daisy sequence with one human Cdk protein and the Cdk proteins from two different kinds of yeast, as shown in the figure. Sequences identical between the human and fungal proteins have been boxed. Such conserved amino acid sequences are often involved in protein-protein interactions. Indeed, the threonine (T) in the central “YTHE/K” block is known to be phosphorylated by a kinase that activates Cdks in human and yeast. The surrounding conserved sequences are assumed to be important for the interaction of this Cdk-activating kinase with Cdk. In the daisy Cdk, however, not all of the amino acids in these conserved blocks match the sequences from yeast and human, as indicated by the arrows marked #1 and #2.
A. When you replace the S. cerevisiae (budding yeast) Cdk with the daisy Cdk, you discover the daisy Cdk does not interact with the Cdk-activating kinase inside the yeast cell. Which amino acid in the daisy Cdk (either the arrow marked #1 or #2) is likely to be the most disruptive to its interaction with Cdk-activating kinase. Explain your answer in two sentences or less.
B. Based on the information in the figure and what you know about the Cdk1–Cdk-activating kinase interaction, would you predict that the human Cdk will interact with yeast Cdk-activating kinase? Explain in one sentence.
human. . .FGIPIRVY TH TLWYR. . . S. pombe S. cerevisiae daisy FGVP . . .FGVP .. . FGAPIKMYTHKIVTLWYR. . . #1 #2Explanation / Answer
The arrow marked #2 seems to be more disruptive because at this position the amino acid E (Glutamic acid) i.e. negatively charged amino acid has been found to be conserved among the various organism but in Daisy it got replaced by K (Lysine) i.e. positively charged amino acid which may disrupt the interaction with the activating kinases. However, arrow marked #1 showing conserved amino acid R (Arginine), positively charged is replaced by K lysine (positively charged) which seem to make hardly any difference regarding interaction with the kinase.
Human Cdk interaction with yeast Cdk-activating kinase is probably not possible because the human has conserved specific sequences for proper interaction. Moreover, Human have multiple CDKs involved at the different stage of cell regulation while yeast has only one Cdk involved.
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