I'm looking for a pdb file of HIV-1 protease without any inhibitors or substrates. So that when I open the pdb file in a molecular viewer, the results look like http://community.middlebury.edu/~sontum/chemistry/students/kim/gkimages/hivprotease1.gif
While the middle burywebsite does provide a pdb download of the structure, the actual pdb id 1HSG" and contains an inhibitor. https://www.rcsb.org/pdb/explore.do?structureId=1HSG
The closest pdb file structure we could find is pdb id 1G6L" and when we open the file in Avogadro, the active site is not visible. http://www.rcsb.org/pdb/explore.do?structureId=1g6l
What are the exact residues in the active site?
Are you sure that it's not 1HSI? On the Middlebury website, I found 3 PDB files with custom names, but each relating to:
Each is complexed with a chemical.
1HSI looks to be the closest to the structure in your figure. Here's a screenshot from Jmol on my computer:
http://www.rcsb.org/pdb/explore.do?structureId=2pc0
Did you search via PDB? I searched there but saw ~1000 crystal structures for this protein!