PROSITE documentation PDOC50250

PCI domain profile

The PCI (for Proteasome, COP9, Initiation factor 3) domain (sometimes also referred to as the PINT domain, for Proteasome subunits, Int-6, Nip-1, and Trip-15) is present in six different subunits of 26 proteasome lid, COP9 signalosome (CSN) and eukaryotic translation initiation factor-3 (eIF3) complexes, as well as in subunits of certain other multiprotein complexes. The PCI domain mediates and stabilizes protein-protein interactions within the complexes. The role of the PCI domains is most likely that of a scaffold for the other complex subunits and other binding partners. The PCI domain could play a role as a universal binding domain supporting intra-complex interactions as well as recruitments of additional ligands [1,2,3,4,5,6].

PCI is an ~190-amino acid domain, not well conserved in its primary sequence, usually located near the C-terminus of the protein. It does not contain any invariant residues or any conserved pattern of charged residues that would suggest a catalytic activity. The PCI domain is comprised of two subdomains that are intimately connected, an N-terminal helical bundle (HB) subdomain and a C-terminal globular winged helix (WH) subdomain (see <PDB:3CHM>). The C-terminal half of the PCI domain is much better conserved than the N-terminal halfdomain [4,5,6].

Some proteins known to contain a PCI domain are listed below:

• Eukaryotic 26S proteasome non-ATPase regulatory subunit 3 (PSMD3).
• Eukaryotic 26S proteasome non-ATPase regulatory subunit 6 (PSMD6).
• Eukaryotic 26S proteasome non-ATPase regulatory subunit 8 (PSMD8).
• Eukaryotic 26S proteasome non-ATPase regulatory subunit 11 (PSMD11)
• Eukaryotic 26S proteasome non-ATPase regulatory subunit 12 (PSMD12).
• Eukaryotic 26S proteasome non-ATPase regulatory subunit 13 (PSMD13).
• Eukaryotic COP9 signalosome complex subunit 1 (CSN1).
• Eukaryotic COP9 signalosome complex subunit 2 (CSN2).
• Eukaryotic COP9 signalosome complex subunit 3 (CSN3).
• Eukaryotic COP9 signalosome complex subunit 4 (CSN4).
• Eukaryotic COP9 signalosome complex subunit 7 (CSN7).
• Eukaryotic COP9 signalosome complex subunit 8 (CSN8).
• Eukaryotic translation initiation factor 3 subunit A (EIF3A).
• Eukaryotic translation initiation factor 3 subunit C (EIF3C).
• Eukaryotic translation initiation factor 3 subunit E (EIF3E).
• Eukaryotic translation initiation factor 3 subunit K (EIF3K).
• Eukaryotic translation initiation factor 3 subunit L (EIF3L).
• Eukaryotic translation initiation factor 3 subunit M (EIF3M).
• Eukaryotic PCI domain-containing protein 2 (PCID2), a component of the transcription and export complex 2 (TREX-2 complex) that functions in docking export-competent ribonucleoprotein particles (mRNPs) to the nuclear entrance of the nuclear pore complex (nuclear basket).
• Eukaryotic germinal-center associated nuclear protein (GANP), a component of the transcription and export complex 2 (TREX-2 complex) that functions in docking export-competent ribonucleoprotein particles (mRNPs) to the nuclear entrance of the nuclear pore complex (nuclear basket).

The profile we developed covers the entire PCI domain.