Insulin is a protein hormone that functions as two polypeptide chains whose amino acid sequences are as follows:
A chain: GIVEQCCTSICSLTQLENYCN
B chain: FVNQHLCGDHLVEALYLV CGERGFFYTPKT
b. Considering the amino acid sequences, suggest how these two polypeptide chains might be held together in an active insulin molecule.

Question

Insulin is a protein hormone that functions as two polypeptide chains whose amino acid sequences are as follows:

A chain: GIVEQCCTSICSLTQLENYCN

B chain: FVNQHLCGDHLVEALYLV CGERGFFYTPKT

b. Considering the amino acid sequences, suggest how these two polypeptide chains might be held together in an active insulin molecule.

Accepted Answer

All right. Hello everyone. So this question says given the amino acid sequences of the two hypothetical protein subunits, alpha and beta as follows. After which we're given the amino acid sequences of both side chains here or both protein subunits determine how these two chains might be held together in the active protein complex option. A says disulfide bond B says hydrogen bond C says hydrophobic interaction and D says all of the above. So as mentioned before, right here on the top of the screen, we have the amino acid sequences of both the alpha and beta chains. So when trying to understand which interactions are possible between these two chains, there are a few different steps that we should keep in mind. The first step is to look or the steep. And the one letter abbreviation of Sistine is simply the letter C. This is because if you have cysteine residues on both chains, a disulfide bond between the two is going to be possible and therefore an answer choice. So going back now to our sequences, all you would need to do is look for letter C and here we do see it because the alpha chain, for example, has two cysteine residues and the beta chain has one cysteine residue. So disulfide bonds are going to be possible between the two since they both have cysteine. So we definitely know that a that a disulfide bond is going to be an answer, but we also have to consider the other interactions. So here for the other interactions, it's important to consider others such as hydrogen bonding, right ionic bonds as well and also hydrophobic interactions between our nonpolar amino acids. So first, let's start with the hydrophobic amino acids. This would include nonpolar amino acids like valine, leucine, alanine and so on. So going back to the structure of the alpha chain, we have a veiling residue and we have a lucine residue. So even though this is only a small subset of the nonpolar amino acids available, recognizing their presence in the structure is going to have or is evidence that the alpha chain is capable of a hydrophobic interaction. So the question is, does the beta chain have a hydrophobic amino acid? And the answer is yes. Right, because the beta chain includes amino acids such as prolene, abbreviated as P and phenylalanine, both of which are nonpolar and can engage in hydrophobic interactions. So c is definitely going to be correct as well. So now what amino acids are capable of hydrogen bonding? Well, those would be our polar amino acids such as sine threonine and tyrosine. So, ST and Y respectively, these are just examples of a of amino acids capable of h bonding. And it just so happens that they're present in both because here we have threonine and sine as well as tyrosine on the alpha chain and on the beta chain, we have 23 inning residues and two series actually. So that is more than enough evidence that hydrogen bonding is also possible between both side chains. And so because all three interactions listed are possible, our correct answer is going to be option D all of the above and there you have it. So with that being said, thank you so very much for watching and I hope you found this helpful.

Verified video answer for a similar problem:

Key Concepts

Protein Structure

Disulfide Bonds

Protein Folding and Function