Komiyama et al. investigated the bicarbonate binding site on the crocodile hemog

Question

Komiyama et al. investigated the bicarbonate binding site on the crocodile hemoglobin by constructing human-crocodile chimeric hemoglobins in which amino acids in the human hemoglobin were replaced with amino acids found in the crocodile hemoglobin at the same location. (The investigators wanted to see if they could make a synthetic human hemoglobin that resembled the crocodile hemoglobin in terms of its ability to bind bicarbonate anions.) They found the bicarbonate binding site to be located at the alpha 1 beta 2-subunit interface, where the two subunits slide with respect to one another during R <-> T transitions. Based on their results the authors modeled a stereochemically plausible binding site that included the phenolate anion of Tyr 41Beta, the epsilon-amino group of Lys 38Beta, and the phenolate anion of Tyr 42alpha. What kinds of interactions do you think the aforementioned amino acid side chains will have with the bicarbonate anion? (It might be helpful to draw the Lewis electron dot structure of bicarbonate).

Explanation / Answer

Based on the given data, the amino acids at bicarbonate binding site are:

Thus, the HCO3- (bicarbonate ion) form an hydrogen bond with –OH group of the tyrosine and the oxygen of HCO3- binds with hydrogen in NH3+ of Lysine. The interactions are coordinated covalent.

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