The image below shows part of the cartoon structure of an important human protein heterodimer.

Three amino acids have been highlighted in a ball and stick representation. Note that atoms are coloured by elements, where nitrogen is blue and oxygen is red.

In the box below, enter the sequence of the highlighted three amino acids in the correct sequence direction of N- to C-terminal according to the protein structure shown.

Your answer must be in the single amino acid code. For example, if you think the sequence is alanine glycine serine, then enter: AGS. Use the provided amino acid figure to help you.