Protein function

[question]

I am facing a problem where i am not sure if a specific protein like for example pituitary folate receptor alpha subunit has the same function, size and structure in any locations of a human body.

 

as i know a gene can have different start and end signal which means a transcript will end in different products then how come a specific pituitary protein will be identical to other places?

 

 

Any ideas are greatly appreciated.

[rakuenso]

I'm not an expert on protein folding, but here goes:

 

protein folding is not always guaranteed to end up being the same everytime even if its AA sequence is the same. Take example prions, which has perfectly normal AA Sequences despite the fact that it is infectious. There are a few protein-folding enzymes that can be regulated via gene expression.

 

But as for the genetic transcripts responsible, every eukaryotic gene has a basal promoter and possibly an upstream promoter. The basal promoter should be the same in all circumstances because that's what the GTF's need to bind to. The upstream promoter's sequences can vary. Also, most transcription start only with AUG coding for methionine, so there really shouldn't be different products in different places if the gene is the same.

[Mokele]

If you're looking for "How do I know if it's the same product of the gene in each place?", can't you make an antibody for the protien, label it, and then dose tissue samples from various body parts with it? In theory, AFAIK, the antibody should only stick to the form of protien it was "made for", not transcriptional of conformational variants.

 

Mokele

[Yggdrasil]

A gene does not necessarily make the same protein in different cells or even within the same cell in different conditions. There is a phenomenon known as alternative splicing can change the sequence of the mRNA transcripts of a gene, resulting in different gene products. Alternative splicing can greatly change the structure and function of various proteins. Many researchers believe that most of the complexity in human beings arises from the alternative splicing of our genes.

 

Probably the best assay to use would be the one Mokele described. If you have reason to believe your gene may be alternatively spliced, you can try to identify variants of your protein by performing 5'-RACE (Rapid Amplification of cDNA Ends).

[rakuenso]

Like I previously said, I'm no expert on proteins, But wouldn't the epitopes be very similar amongst the "variants" since they would've been arranged from very similar AA Sequences?

[Yggdrasil]

Yes, sometimes antibodies cannot distinguish between alternatively spliced versions of proteins.

[Helix]

Well if it's the same gene then the protein should obviously be the same, excluding the chance of a mis-fold.

 

Protein "X" will have the same general function anywhere due to the fact it's the same protein no matter where it is. It might preform a slightly different task in different parts of the body, i.e. clean up different things.

 

But maybe the gene is read differenly in different parts, maybe it is only partially expressed. Then who knows.

[Yggdrasil]

Protein "X" will have the same general function anywhere due to the fact it's the same protein no matter where it is. It might preform a slightly different task in different parts of the body, i.e. clean up different things.

 

Actually, this isn't always true. Proteins can take on different roles under different conditions. For example, phosphofructokinase-2 (PFK-2) is an important protein in the regulation of metabolism. Normally (at high concentrations of glucose), PFK-2 acts as a kinase and phosphorylates fructose-6-phosphate to form fructose-2,6-bisphosphate, an important regulatory molecule which stimulates many enzymes important to glycolysis and the TCA cycle. However, when intracellular glucose levels drop, the resultant rise in cyclic AMP will activate cAMP-dependent protein kinases. These kinases will phosphorylate PFK-2, which inhibits its it kinase active site, but activates is phosphatase active site. Now it catalyzes a completely different reaction, which converts fructose-2,6-bisphosphate back into fructose-6-phosphate. While it is true that PFK-2 acts on the same molecules, usually two proteins are required for such regulaton -- a phosphatase and a separate kinase. PFK-2 is unique among such enzymes because it combines a kinase domain and a phosphatase domain into one molecule, giving a very elegant system for regulating the concentrations of fructose-2,6-bisphosphate.

[Helix]

You're right, my bad. I was speaking generally, but in biology there are always exceptions.