text: user12686: I am developing a bioinformatics framework only for learning purposes. I want to calculate --
  
  dihedral angles
  detect H, E, and C components
  detect Hydrogen bonds
  etc.
  
  Therefore, I want a PDB file that represents a protein with a small chain but is complex enough for me to experiment with.
  Can you suggest such a PDB file?
  
  user73: Insulin, perhaps?
  https://www.rcsb.org/structure/1trz
  From here:
  
  Insulin is a perfect molecule for exploring protein structure. It is small enough that you can display all of the atoms and still have a picture that is not too confusing. Human insulin is pictured here, using entry 1trz. This structure, like many other insulin structures, includes a hexameric complex of the hormone, and only one monomer (composed of one A-chain and one B-chain) is shown here. In the structure, you can see many of the key features that stabilize protein structure. Carbon-rich amino acids, like leucine and isoleucine, cluster in the middle of the molecule, forming a hydrophobic core, and the surface is covered with charged amino acids like arginine and glutamate that interact favorably with the surrounding water. Also notice the three disulfide bridges between cysteine amino acids, which stabilize this tiny protein.
  
  
  user745: Although Insulin is a great, well studied example of a small structure it does have the slight downside of not having any sheet structure in the monomer. There is a small cross-chain sheet between residues 24-26 in both the B and D chains (from https://www.ebi.ac.uk/pdbe/entry/pdb/1zni/ ).
  Another possibility might be crambin (http://www.cathdb.info/version/latest/domain/1ejgA00) which does have a small antiparallel sheet, although it is tiny at only 2 residues per strand.
  A more general approach might be to use something like the top2018 structure set from the Richardson lab (https://zenodo.org/record/5777651#.YtQB59LMJH4) . I used the top500 back in the day, and they are a high-quality set of structures.
  
original_text: 12686: <p>I am developing a bioinformatics framework only for learning purposes. I want to calculate --</p>
  <ol>
  <li>dihedral angles</li>
  <li>detect H, E, and C components</li>
  <li>detect Hydrogen bonds</li>
  <li>etc.</li>
  </ol>
  <p>Therefore, I want a PDB file that represents a protein with a small chain but is complex enough for me to experiment with.</p>
  <p>Can you suggest such a PDB file?</p>
   73: <p>Insulin, perhaps?</p>
  <p><a href="https://www.rcsb.org/structure/1trz" rel="nofollow noreferrer">https://www.rcsb.org/structure/1trz</a></p>
  <p>From <a href="https://pdb101.rcsb.org/motm/14" rel="nofollow noreferrer">here</a>:</p>
  <blockquote>
  <p>Insulin is a perfect molecule for exploring protein structure. It is small enough that you can display all of the atoms and still have a picture that is not too confusing. Human insulin is pictured here, using entry 1trz. This structure, like many other insulin structures, includes a hexameric complex of the hormone, and only one monomer (composed of one A-chain and one B-chain) is shown here. In the structure, you can see many of the key features that stabilize protein structure. Carbon-rich amino acids, like leucine and isoleucine, cluster in the middle of the molecule, forming a hydrophobic core, and the surface is covered with charged amino acids like arginine and glutamate that interact favorably with the surrounding water. Also notice the three disulfide bridges between cysteine amino acids, which stabilize this tiny protein.</p>
  </blockquote>
   745: <p>Although Insulin is a great, well studied example of a small structure it does have the slight downside of not having any sheet structure in the monomer. There is a small cross-chain sheet between residues 24-26 in both the B and D chains (from <a href="https://www.ebi.ac.uk/pdbe/entry/pdb/1zni/" rel="nofollow noreferrer">https://www.ebi.ac.uk/pdbe/entry/pdb/1zni/</a> ).</p>
  <p>Another possibility might be crambin (<a href="http://www.cathdb.info/version/latest/domain/1ejgA00" rel="nofollow noreferrer">http://www.cathdb.info/version/latest/domain/1ejgA00</a>) which does have a small antiparallel sheet, although it is tiny at only 2 residues per strand.</p>
  <p>A more general approach might be to use something like the top2018 structure set from the Richardson lab (<a href="https://zenodo.org/record/5777651#.YtQB59LMJH4" rel="nofollow noreferrer">https://zenodo.org/record/5777651#.YtQB59LMJH4</a>) . I used the top500 back in the day, and they are a high-quality set of structures.</p>
  