December 5, 2018  

List of classifications that may be found in PDB entries.  This list should only be used as a guide, and will be expanded in the future. 

ALLERGEN
ANTIBIOTIC (peptidic, saccharide containing)
ANTIFREEZE PROTEIN
ANTIFUNGAL PROTEIN
ANTIMICROBIAL PROTEIN
ANTITOXIN
ANTITUMOR PROTEIN
ANTIVIRAL PROTEIN
APOPTOSIS
ATTRACTANT
BIOSYNTHETIC PROTEIN
BLOOD CLOTTING
CARBOHYDRATE
CELL ADHESION
CELL CYCLE
CELL INVASION
CHAPERONE
CIRCADIAN CLOCK PROTEIN 
CONTRACTILE PROTEIN
CYTOKINE (includes interleukins, interferons)
DE NOVO PROTEIN (ARTIFICIALLY DESIGNED, OFTEN SYNTHETIC)
DNA 
DNA-RNA HYBRID (used when biological assembly contains mixed DNA and RNA residues or strands)
ELECTRON TRANSPORT
ENDOCYTOSIS
EXOCYTOSIS 
FLAVOPROTEIN
FLUORESCENT PROTEIN
GENE REGULATION (use only when TRANSCRIPTION, REPLICATION, TRANSLATION are not applicable) 
HORMONE
HYDROLASE (E.C.3.-.-.-)
IMMUNE SYSTEM (includes antibodies, antigens)
IMMUNOSUPPRESSANT
ISOMERASE (E.C.5.-.-.-)
LIGASE (E.C.6.-.-.-)
LIPID TRANSPORT
LUMINESCENT PROTEIN
LYASE (E.C.4.-.-.-)
MEMBRANE PROTEIN (no other function known)
METAL TRANSPORT
MOTOR PROTEIN
NEUROPEPTIDE
ONCOPROTEIN
OXIDOREDUCTASE (E.C.1.-.-.-)
OXYGEN BINDING 
OXYGEN STORAGE
OXYGEN TRANSPORT
PHOTOSYNTHESIS
PLANT PROTEIN (no other function known)
PROTON TRANSPORT
PROTEIN TRANSPORT (a protein involved in transporting other protein)
RECOMBINATION
REPLICATION
RIBOSOME (use only when TRANSLATION is not correct; do not specify /RNA even when present!)
RIBOSOMAL PROTEIN 
RNA
SIGNALING PROTEIN (includes G-proteins)
SPLICING
STRUCTURAL GENOMICS (product of a probable gene)
STRUCTURAL PROTEIN
SURFACTANT PROTEIN
TOXIN (not antibiotic, can use e.g. HYDROLASE INHIBITOR, TOXIN)
TRANSFERASE (E.C.2.-.-.-)
TRANSCRIPTION (DNA to RNA)
TRANSLATION (protein synthesis; prefer over RIBOSOME)
TRANSLOCASE (E.C.7.-.-.-)
TRANSPORT PROTEIN (a protein that transports anything)
NUCLEAR PROTEIN (whether involved in binding RNA/DNA or some sort of nuclear processing is unclear)
VIRUS (for entire viral capsid)
VIRAL PROTEIN (viral protein not involved in the viral capsid)
VIRUS LIKE PARTICLE ((for cases where virus like particles are assembled , but are not the standard virus) 
When no other function is known use the following:
CHOLINE-BINDING PROTEIN
CYTOSOLIC PROTEIN (a protein whose function is not known well but is known to be found in the cytosol of a cell.)
DNA BINDING PROTEIN
RNA BINDING PROTEIN
LIPID BINDING PROTEIN
METAL BINDING PROTEIN (such as ZN, FE)
PEPTIDE BINDING PROTEIN
PROTEIN BINDING (implies binding of protein by protein)
SUGAR BINDING PROTEIN
xxx-BINDING PROTEIN (for any xxx ligand if none of above applies, such as HEME, AVIDIN, BIOTIN)
PROTEIN FIBRIL
UNKNOWN FUNCTION