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Do we know all the proteins (and their primary structure!)?

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Do we know all the proteins (and their primary structure!)?

Postby Julie5 » Thu Apr 28, 2011 9:35 am

Again, one of those 'basic' questions that I realise I simply don't know the answer to!

Do we know all the proteins in living organisms? Or even in humans? Or are there still unknown proteins whose existence we haven't realised yet?

If we do know all the proteins in the (human) proteosome, do we know their primary structure?

I am sort of assuming we do, because we now have the human genome, and we now know (don't we?) just how many protein-coding genes there are (don't we??)

Perhaps I should say I think we know all the polypeptides rather than the proteins (allowing for unknown secondary/tertiary/quaterary structures of the proteins to which those pp chains contribute)?

Or am I being naively optimistic?!

Many thanks for any light shed - Regards, Julie.
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Postby Babybel56 » Thu Apr 28, 2011 11:13 am

I think it would be safe to say that we know the structure of every human protein, but as far as conformation and function of each one, as well as variability, we cannot be sure. To discover this sort of thing you don't just need the peptide sequence, but to observe it in action. For many things this requires a high concentration of that particular protein (so ion channels in the electric organ of the torpedo fish for example) and some are just too rare to get this.
Some properties can only be observed through crystellising proteins, and this is a very difficult process with transmembrane proteins. This is why making drugs for certain receptors isn't a simple task, because we can't know exactly what size and shape these drugs need to be.

I suspect for non-mapped genomes there are going to be a lot of proteins we still don't know. There's just so much variation available!
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Postby JackBean » Fri Apr 29, 2011 8:30 am

by knowing protein, we must know it's primary structure (or we can also know, there is some enzyme catalyzing some activity, of which we do not know the gene, truth. But nowadays we have rather opposite problem).
We have predicted genes and thus predicted proteins in human, but that doesn't guarantee, that we don't have some false positive or false negative ;)

And the difference between polypeptide and protein is only in size, not in known level of structure ;)
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Postby stephroche » Fri Apr 29, 2011 1:57 pm

We do not know every protein sequence. The genes do not code to the post traductionnal modifications. As exemple, on the collagen sequence, we have a repeat of proline but in the real molecule, some aa are hydroxyproline.

In addition, some protein need to loose a peptide to be active or to modify their activity. So these protein have not the same sequence and primary structure.
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Postby Cat » Mon May 02, 2011 4:04 am

"Do we know all the proteins in living organisms?"

No!!!

It is impossible to even predict even primary structure of all proteins from DNA sequence.

Just consider the scheme:

DNA-> mRNA-> mRNA splicing? -> protein chain -> post translational modifications (which ones? protein splicing?)
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Postby JackBean » Wed May 04, 2011 9:41 am

Why should it be impossible? Even nowaydays we are often able to predict the splicing. And posttranslational modifications are not part of primary structure (unless it's Hyp in collagen as mentioned above)
http://www.biolib.cz/en/main/

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