Final answer:
The HSP-70 protein transitions from an 'open' conformation when ATP is bound to a more 'closed' conformation upon binding ADP, assisting in the proper folding of substrate proteins.
Step-by-step explanation:
The conformation of HSP-70 when bound to ATP versus when it is bound to ADP differs significantly. When ATP is bound, HSP-70 is generally in an 'open' conformation, which allows for the initiation of protein folding or the binding of an unfolded polypeptide. Upon hydrolysis of ATP to ADP, HSP-70 undergoes a conformational change to a more 'closed' state, which tightens its hold on the substrate polypeptide, thus facilitating the proper folding of the substrate protein. The terms open and closed relate to the substrate binding domain of HSP-70 and not to secondary structures like alpha-helix or beta-sheet.