NOTE: a new, up to date version is available (it is currently being updated)

NOTE2: a new version of 3dcomplex is also available (it is currently being updated)

PiQSi is a community effort that facilitates the investigation and curation of quaternary structures. Given a PDB identifier or a protein sequence, it displays information about the quaternary structure of homologous proteins on a single web-page. This information allows a quick comparison of the quaternary structure(s) of the members of a protein family. So far, the web-server has allowed the manual curation of ~15000 structures of PDB Biological Units, of which about 15% were found to be likely errors (e.g. guilty).

NEW Several features have been added in this new release!

Please, register and participate to the quaternary state annotation of PDB structures!

If you would like to refer to PiQSi, please cite:
Levy ED. PiQSi: protein quaternary structure investigation. Structure. 2007 Nov;15(11):1364-7 - Pubmed

Pick of the day - is this protein correct?

This protein is likely to have a wrong quaternary structure because: (i) it does not form a closed symmetry (see help for details on symmetry), and (ii) it shares 100% sequence identity with a symmetric . You can contribute to PiQSi by looking at the paper and annotating the quaternary state :)

Code Pic Error? Sym1 Nsub1 Sym2 Nsub2 SProt Weight Ref H E R Org Fun
1gme_2NA? D312??Q41560151PHERTriticum aestivumCHAPERONE

Illustration of PiQSi information

Each protein can be displayed along with its homologs of known structure, and information that helps to determine the biological oligomeric state.