This server calculates contacts between secondary
structure elements in your PDB file. Per secondary
structure pair all atomic contacts are listed. Contacts
with symmetry related molecules in the crystal are not listed.
A contact is defined as two atoms for which the distance between
the Van der Waals surfaces is less than 0.5 Ångstrom.
WHAT IF uses the following Van der Waals radii: C:1.8 Ångstrom;
O:1.4 Ångstrom; N:1.7 Ångstrom; S:2.0 Ångstrom.
Please keep in mind that two secondary structure elements that
are adjacent in the sequence always contact each other in this
If you have detected any error, or have any question or suggestion,
please send an Email to Gert Vriend.
Roland Krause, Maarten L Hekkelman, Jens E Nielsen,