Hi,

It is possible and known in certain cases. The sequence of amino acids in a protein defines the structure of the protein, however different amino acid sequence may also result in similar structure or conformation. Such as scenario is referred to as convergent evolution towards same function. Here the overall structure of the two proteins may not be same, but the conformation of the catalytic site (or region responsible for the known activity) may be very similar if not same. If the structures of the two proteins are knows, a structural alignment of such regions may be performed to assess this.

Dear Magdalena Karlikowska ,

This is quite a broad question and can be caused by multiple reasons. As said by Ajay Saini in some case the crucial regions might be conserved and thereby its function(s). Another reason might be that amino acids have certain physicochemical properties that can be more or less interchangeable (helical tendency, charge, hydrophobicity etc.).

See for examples the alignments of SecA and SecD for example. Same proteins with same function but with quite some degree of difference in amino acid sequence (and length):

Article Identification and in silico analysis of helical lipid bindi...

Article Prediction of Lipid-Binding Regions in Cytoplasmic and Extra...

Hope this answers your question somewhat.

Best regards.

Magdalena Karlikowska Have you heard about the Isoenzymes? Two different enzymes (varies in sequences as well as structures) catalysing the same reaction i.e. having same function. Its the same concept here in your case. You can read more about this. The reasons could be as explained by Ajay Saini and Rob Keller