A subsection of the designated chain can optionally be specified for both the target and query structure. When the From (respectively To) field is left blank, then the starting (resp. ending) residue is taken to be the first (resp. last) residue sequence number of the designated chain. When filled, the From and To fields should contain residue sequence numbers as appearing in the PDB file.
The chain ID for both query and target structure must be given. If the PDB file has a blank in the column for chain ID, then underscore (default) must be entered.