Reference:
  Author: E. Krissinel and K. Henrick
  Title: "Secondary-structure matching (SSM), a new tool for fast protein structure alignment in three dimensions"
  Journal: Acta Crystallogr D Biol Crystallogr.
  Year: 2004
  Volume: 60
  Number: 1
  Pages: 2256-68
  DOI: 10.1107/S0907444904026460
  PMID: 15572779
  URL: http://scripts.iucr.org/cgi-bin/paper?S0907444904026460
  eprint: http://journals.iucr.org/d/issues/2004/12/01/ba5056/ba5056.pdf
