Protein families arise when a protein sequence that generates a stable fold dive

Question

Protein families arise when a protein sequence that generates a stable fold diverges over many generations and acquires new functions. One example of this can be seen in the globin family. Myoglobin (below, on the left) is a stable monomeric protein that can help carry oxygen using a heme molecule (cofactor). Hemoglobin (below, on the right) is functional only as a tetramer. It also carries oxygen using heme groups, over a much more dynamic range of oxygen than myoglobin. The "globin fold is structurally conserved across these proteins, but the ability to tetramerize arose through genetic drift and natural selection. Thinking back about what we learned about DNA sequence mutations and their effect on protein structure, provide an explanation for how changes in the globin sequence of these two proteins can still produce the same overall fold (i.e. alterations that conserve protein structure) but have slight differences in the protein's ability to multimerize (i.e. alterations that alter protein-protein interactions). What kind of mutations might promote multimerization and where would you expect these changes to be within the overall protein structure? but it is useful N-terminus Cterminus C terminus Myoglobin Hemoalobin

Explanation / Answer

Answer) We know that Hemoglobin and myoglobin molecules share only 27% identity in their sequence of amino acids. yet their secondary structure folds in a similar manner except hemoglobin have tetrameric tertiary structure. there are 2 kinds of general mutations in amino acid sequence; a) non-synonymous substitution - which results in missense mutation that alters the amino acid at a specific position in the sequence. b) synonymous substitution - which does not alter the overall structure and property of the protein but changes the one amino acid into another similar type of amino acid. such synonymous substitution in the primary sequence important for folding of protein does not alter the secondary structure of the protein (conserve protein structure). non-synonymous substitutions in the hydrophilic domain of the protein alter its interaction with the external environment in the tertiary structure (alters protein-protein interactions). Alterations in the hydrophilic domain (exposed surface domain) of the protein will result in the multimerization. these are the mutations that allow cooperative binding between monomeric subunits of hemoglobin.

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