Question

In protein crystallization, what is a common observation concerning the presence of ions in the finished crystal structures?

A) High concentrations of sodium and potassium ions are visible
B) Chloride ions are often observed in periodic structures within crystals
C) Crystals typically show fewer ions than expected despite their presence
D) Presence of ions is consistent with physiological KCl concentrations

Does having KCl or NaCl at normal physiological levels affect protein crystallization?

A) Physiological levels of KCl or NaCl prevent proteins from crystallizing
B) Physiological salt levels facilitate better protein crystallization
C) High concentrations of these salts always result in superior protein crystals
D) Normal physiological salt levels have no effect on protein crystallization

Answer 1

Protein crystals typically show fewer ions than expected due to the salting-out effect caused by high salt concentrations. Nevertheless, physiological salt levels do facilitate protein crystallization by reflecting the protein's natural environment. option (B)

Step-by-step explanation:

In protein crystallization, a common observation is that crystals typically show fewer ions than might be expected given their presence in solution. When ions such as sodium and potassium are added in high concentrations, they associate with water molecules, which reduces the protein-water interaction and instead increases protein-protein interactions. This phenomenon is known as the salting-out effect, and it can lead to the precipitation of proteins.

The ions are observed in protein crystal structures, but the effect of physiological levels of salts like KCl or NaCl on protein crystallization can vary. Whilst high concentrations of these salts can enhance crystallization due to the salting-out effect, physiological salt levels can also be conducive to protein crystallization because they reflect the natural environment of the protein, which can facilitate proper folding and stability.