Objectives for protein section II. Explain conformational changes in proteins. Explain how GTP binding & hydrolysis allows ras & other G-proteins to function as molecular on/off switches. Discuss the relationship of ras normal function, ras mutants, & ras’ role in cancer.
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mitosisRas is a molecular on/off switch
Conformational change = a predictable change in protein structure that is associated with biological activity.
Conformational change could be due to the binding of another protein, a certain nucleotide, the addition of a phosphate, etc…
g -phosphate can be
hydrolyzedRibbon Cartoon of Ras with GTP
From C. Branden & J. Tooze. 1999. Introduction to Protein Structure, 2nd Ed.
With GTP, more of switch I becomes b sheet.
This b strand forms a b sheet with 2 strands in raf.
The preceding function of ras is required for the proper function of all NORMAL mammalian cells. Ras only participates in the development of cancer when the gene for ras is mutated (an oncogene) and the resulting ras protein functions incorrectly (an oncoprotein).
Essential glycines (gly-12) required to position GTP
Glutamine-61 required for
Rap1A binds to raf and is involved in the same signaling pathways, so you would expect its structure to be most similar to ras.
1. Explain why rap1A is located closer to the ras proteins than the other proteins are.
2. Explain the grouping of rac1 and rhoA together on a branch.
3. Explain the grouping of ran and arf1 together on a branch.
Rac1 and rhoA are both involved in signaling via cadherins and the actin cytoskeleton. They share the most functions, so they are the most similar to each other.
Ran and arf1 share somewhat similar functions in that they are both involved in transport within the cell, so they are similar. However, their functions are very distinct, & so are their sequences.
Green = 100% identical
Yellow = many identical
Blue = similar
#s = AA # based on human N-ras
gly-10, gly-15, lys-16, thr-35, asp-57, gly-60, lys-117, asp-119, ala-146
The one function that all of these proteins share is the binding of GDP/GTP; therefore, you would predict that the most commonly shared AAs would be those involved in binding the nucleotide.
The 9 completely conserved AAs ( structuresgreen) in our G protein examples are located precisely around the nucleotide (blue) and most bond with it.
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