Question

Is it possible for naturally produced proteins to have different functions without any change in amino acid sequence or nucleotide sequence? How?

Answer 1

Your question is if the same naturally produced sequence has different functions without any change in nucleotide sequence OR amino acid sequence. The answer is YES

Revising the Central Dogma of Molecular Biology where DNA sequence is transcribed into mRNA sequence (heterogeneous nuclear RNA in eukaryotes, after post-transcriptional modification, is formed final mRNA sequence which travels out to cytoplasm) and then mRNA with the help of tRNA and ribosome along with other factors mRNA is translated into a polypeptide. Once a polypeptide is formed, it undergoes secondary, tertiary, and quaternary structures depending on the functional groups involved. So basically, one amino acid sequence should give rise to some kind of folding but sometimes it may vary, we will see WHY?

Coming to each point individually :

1. No change in nucleotide sequence :

If there is no change in the nucleotide sequence, the same protein is expected to be formed. This happens in organisms where no post-transcriptional modification is required. But in eukaryotes depending on the tissue-specificity, in the recent researches, the phenomenon of Alternate Splicing comes into picture while post-transcriptional modification wherein it allows the different intronic sequence to get spliced leading to different mRNA transcripts which gives rise to the formation of different polypeptide sequences and henceforth different proteins and ultimately different functions. This is one of its cases.

2. No change in amino-acid sequence :

Now this seems to be weird that how even after having the same amino acid sequence, how will the protein differ in its structure and function. Even the nucleotide sequence is the same along with the amino acid sequence. So, here some additional information is required. The translation process occurs either in the cytoplasm or on the ribosomes lying on the Rough Endoplasmic Reticulum (RER). Once this process is over the naive polypeptide chain is released into the cytoplasm or in the RER, it is protected by heat shock proteins (hsps) also called Chaperons, which helps in post-translational modification of the polypeptide formed and plays a major role in the proper folding of the protein. So now, if Chaperons seem to be defective/ mutated, they do not perform their function properly, and the naive polypeptide gets folded in a disordered fashion, which can lead to a different type of secondary or tertiary structure formation and ultimately different functional properties.

Thus, either during the post-transcriptional or the post-translational modification, minute mistakes or variations can lead to change in the function of the naturally produced proteins. Thus, the regulatory steps are also essential.

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