Final Answer:
A change in protein structure is least likely to arise from a point mutation in a regulatory region of a gene.
Step-by-step explanation:
Point mutations in regulatory regions of genes typically affect the binding of transcription factors, altering the gene's expression levels rather than the structure of the protein it encodes. Regulatory regions, such as promoters and enhancers, control the initiation and rate of transcription. Point mutations in these regions can lead to increased or decreased gene expression by influencing the binding affinity of regulatory proteins.
In contrast, mutations in coding regions of a gene, such as missense mutations, can result in changes to the amino acid sequence of the protein, potentially affecting its structure and function.