Question

Consider a 55 kDa* protein, which is a homodimer with its two α-helical subunits interacting through a coiled-coil motif (leucine zipper). If the mean amino acid residue mass is about 110 Da, estimate the number of the amino acids residues in each subunit (round down to the nearest residue).

Answer 1

*1 kDa = 1,000 Da. 1 Da ("Dalton") is a molecular weight unit equivalent to 1 g/mol (find it in the gloassary of your textbook). A 55 kDa protein has a molecular mass of 55,000 gr/mol.

Answer 2

Would you do 55000 Da/110 Da ?

Answer 3

Since you have 2 subunits due to the homodimer, 1 subunit is half of 55kDa.


((55,000/2) / 110) = # of amino acids in a subunit.