What determines the shape of a protein?
A protein's shape is mainly determined by the sequence of amino acids that make up the protein.
A protein's shape is determined by the sequence of amino acids that make up the protein. The order of the amino acids, or the primary structure, determines the folding of the amino acid chains or tertiary structure.
The image below shows amino acids along with their R-groups or side chains. The interactions between the side chains and the amino acids determine the folds of the protein.
You can read in more detail about what determines the shape of a protein at Nature's webpage on the topic.