The antifreeze protein MpAFP is composed of four subunits with a pipe-like structure. Each subunit is composed of 13 ring-like repeating structures with sequence motifs of 19 amino acids. Upon characterizing the structural ring, it contains hydrophilic and hydrophobic amino acids, which bind to the water in the ice nucleus and prevent its growth. These acids also create a bond with the calcium ions that are found between every set of two loops and assist in stabilizing the structure and function of the protein. The calcium ions create the suitable fold of XGTGND, so that between Glycine at position 82 in the protein and the amino acid Aspartate at position 84 in the protein, a space is created perfectly fitted for binding an ice crystal.

18. In antifreeze proteins there are a number of structural characteristics, which prevent the formation of significant ice crystals in the cell. Determine the sequence of steps, which ultimately prevent the formation of these ice crystals:

An arbitrary sequence of steps:

Step 1:
Step 2:
Step 3:
Step 4:

The correct sequence is: calcium ions stabilize the ring-like structure ➔ polar groups in the ring structure bind to water molecules ➔ an ice sheet like structure is created in which the water molecules are spread one next to the other ➔ the solidification of water molecules into significant crystallization nuclei is prevented.

19. In this activity we saw that calcium ions stabilize the ring-like structures