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Name: Jaime
Status: Student
Grade:  12+
Location: WA
Country: United States
Date: January 2009

How is it possible to have two proteins that have two different functions that are made of exactly the same amino acids?

Proteins often consist of multiple parts, known as domains, that have distinct functions, so a single protein may have multiple functions in the cell. For example, proteins called transcription factors regulate the expression of genes by having a domain which binds the DNA as well as a different domain which binds the machinery of the cell that is involved in transcribing the gene.

There are plenty of examples of proteins which function in disparate pathways. One of the most intensely studied genes in the human genome, p53, is one of the most important genes in cancer biology and is thought to consist of seven domains. p53 acts as a transcription factor and, upon cell damage, binds DNA to induce the expression of genes which prevent the cell from dividing. In addition, cell damage can lead p53 to interact with and activate proteins involved in programmed cell death, also known as apoptosis. By having domains which are involved in these two distinct functions, stopping damaged cells from dividing and causing them to "commit suicide," p53 plays a key role in preventing damaged cells from becoming tumors.

Ethan Greenblatt
Ph.D. Candidate
Stanford Biophysics

First of all, if two "different " enzymes have the same amino acid sequence, they are not different. Although I don't know of any examples of an enzyme or protein with two different functions, if one exists, it could be explained by the fact that the genes for two different proteins became fused during evolution and now these "two" proteins are fused and retain the two functions of the formerly separate proteins.

Ron Baker, Ph.D.

There are many nutrients, including proteins, that perform multiple functions. If there had to be one and only one specific protein for every life function, I don't think we would be here -- at least not in our present form.

Vince Calder

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