parallel/antiparallel database

you can query by pdbid here
http://oca.ebi.ac.uk/oca-bin/csu?PDB_ID=1l6z

or you can read pdb file accourding to columns 39-40 in pdb's doc
http://www.rcsb.org/pdb/docs/format/pdbguide2.2/part_44.html