The protein verification tools from the WHAT IF program are available as a free stand-alone program, complete with all source code. Please look at the documentation that is available for the WHAT_CHECK output.
Commercial and non-commercial users are free to download WHAT_CHECK, and use it for all forms of research and education. However, there are some restrictions:
So, WHAT_CHECK is for your research/education purposes only. Of course, industry can sell all products produced using WHAT_CHECK without restrictions, but nobody can start selling WHAT_CHECK reports, and nobody is allowed to make a WWW server that produces WHAT_CHECK results or modified WHAT_CHECK results.
WHAT_CHECK. This is the "official" WHAT_CHECK reference
Errors in protein structures.
R.W.W. Hooft, G. Vriend, C. Sander, E.E. Abola, Nature (1996) 381, 272-272.
DSSP. DSSP determines secondary structures. You need a special license for using
DSSP. WHAT_CHECK works slightly worse in a few options if you don't have DSSP available.
Dictionary of protein secondary structure: pattern recognition of hydrogen bond and geometrical features.
W.Kabsch and C.Sander, Biopolymers 22, 2577--2637 (1983).
WHAT IF. This is the official WHAT IF reference. WHAT IF is by now the mother
of all molecular software packages....
WHAT IF: a molecular modelling and drug design program.
G. Vriend, J. Mol. Graph. 8 52--56 (1990).
Bond lengths and angles.
Accurate Bond and Angle Parameters for X-ray Protein Structure Refinement.
R.Engh and R.Huber, Acta Cryst. A47, 392--400 (1991).
New parameters for the refinement of nucleic acid-containing structures.
Parkinson, G.; Voitechovsky, J.; Clowney, L.; Brünger, A.T.; Berman, H. Acta Cryst. D52, 57--64 (1996).
Matthews Coefficient.
Solvent Content of Protein Crystals
B.W. Matthews
J. Mol. Biol. 33, 491--497 (1968).
Puckering parameters.
A general definition of ring puckering coordinates
D.Cremer and J.A.Pople, J. Am. Chem. Soc. 97, 1354--1358 (1975).
Quality Control for directional atomic contact analysis.
Quality control of protein models: directional atomic contact analysis.
G.Vriend and C.Sander, J. Appl. Cryst. 26, 47--60 (1993).
Symmetry Checks.
Reconstruction of symmetry related molecules from protein data bank (PDB) files.
R.W.W.Hooft, C.Sander and G.Vriend, J. Appl. Cryst. 27, 1006--1009 (1994).
Hydrogen bond networks and His, Asn, and Gln flips.
Positioning hydrogen atoms by optimizing hydrogen bond networks in protein structures.
R.W.W.Hooft, C.Sander and G.Vriend, PROTEINS (1996) 26, 363-376.