significant sequence identity?

Question

[silvia.caprari84]

Hi,

could you tell me when I can define the sequence identity between two proteins significant?In general, I knew that sequences with more 30% sequence identity are considered similar, and below no..Could you confirm that?

Thank you very much.

Silvia

Answer 1

[mxs]

Yes/No.

It is true that sequences with 30% identity and above exhibit structural and thus functional relatedness (which you might interpret as homology given that you are referring to the concept from its evolutionary perspective - which is what people usually do and how excess similarity is interpreted in alignment search strategies.) However, saying that something with 15% identity is insufficiently similar to reflect some common ancestry is wrong. 15% identical sequences can also be homologous. That is why it is better to use measure of expectation (e-value) for inferring homology through common ancestry than percent identity.

Bottom line is, given the evolutionary frame of reference you can be almost certain that 30% identity implies common ancestry and thus homology, but you cannot say that 25%,20%,15%,10%,5%... identity does not.

cheers

mxs

[xuechun]

Is there have any papers to support these? Will you share some reporters?