Final answer:
To perform a BLASTX search, you should use the Entrez Protein database to compare protein sequences.
Step-by-step explanation:
The BLASTX search is performed to compare protein sequences. The appropriate database to use for this search is the Entrez Protein database, which contains precalculated BLAST results. By opening the Links menu for your protein, you can access the relevant protein sequences extracted from the PDB (Protein Data Bank) 3-dimensional structure records.