the open access publication charges for this paper has been waived by oxford university press .
 pdbselect ( http://bioinfo.tg.fh-giessen.de/pdbselect/ ) is a list of representative protein chains with low mutual sequence identity selected from the protein data bank ( pdb ) to enable unbiased statistics . 
 the list increased from 155 chains in 1992 to more than 4500 chains in 2009 . 
 pdbfilter - select is an online service to generate user - defined selections . 
FUNDING