Question

A glycosaminoglycan is a polymer (repeating units) of an amino sugar (N-acetylglucosamine or N-acetylgalactosa mine) along with an uronic sugar (glucuronic acid or iduronic acid) or galactose. Plasma proteins have been studied for their ability to bind to these polymers. One such protein, kininogen, is lysine-rich.

a) Do you expect kininogen to bind glycosaminoglycans effectively? Why or why not?

b) Do you expect the binding of kininogen to be less sensitive, more sensitive or about the same to changes in the pH around physiological conditions? Briefly justify your answer.

c) You are a researcher and you propose that instead of using Histidine-Proline-Rich glycoprotein (HPRG) as a plasma pH sensor, you think that your lab should use Lysine rich protein. Sketch a binding curve that you would expect from this lysine-rich protein and outline major similarities and differences in binding between this lysine-rich protein and HPRG. Make sure to directly reference your plot in your answer

Answer 1

A) yes, GAGs have a negative charge and lysine carry a positive charge, thus they both would interact effectively through electrostatic interactions.

B) if the pH is either decreased i.e. become more negative there won't be any change in the binding affinity as a decrease in pH won't remove the charge on the lysine. However, an increase in pH would dissipate the positive charge as a proton from lysine is transfered to the alkine solution with less number of protons .In this case the binding affinity would decrease.