thumb|400px|Schematic representation of structural classes of protein according to the [[CATH database|CATH classification scheme.]]
Proteins are a class of macromolecular organic compounds that are essential to life. They consist of a long polypeptide chain that usually adopts a single stable three-dimensional structure. They fulfill a wide variety of functions including providing structural stability to cells, catalyzing chemical reactions that produce or store energy or synthesize other biomolecules including nucleic acids and proteins, transporting essential nutrients, or serving other roles such as signal transduction. They are selectively transported to various compartments of the cell or in some cases, secreted from the cell.
This list aims to organize information on how proteins are most often classified: by structure, by function, or by location.
Structure
Proteins may be classified as to their three-dimensional structure (also known a protein fold). The two most widely used classification schemes are:
- CATH database
- Structural Classification of Proteins database (SCOP)
Both classification schemes are based on a hierarchy of fold types. At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins.
While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. Finally other proteins appear not to adopt any stable conformation and are referred to as intrinsically disordered.
Proteins frequently contain two or more domains, each have a different fold separated by intrinsically disordered regions. These are referred to as multi-domain proteins.
Function
[[Image:Human genome by functions.svg|thumb|475px| The human genome, categorized by function of each gene product, given both as number of genes and as percentage of all genes.
Structural
Protein#Structural proteins
Catalytic
Enzymes classified according to their Enzyme Commission number (EC). Note that strictly speaking, an EC number corresponds to the reaction the enzyme catalyzes, not the protein per se. However each EC number has been mapped to one or more specific proteins.
- List of enzymes
- EC 1: Oxidoreductases
- EC 2: Transferases
- EC 3: Hydrolases
- EC 4: Lyases
- EC 5: Isomerases
- EC 6: Ligases
- EC 7: Translocases
Transport
Transport protein
- Ion channel
- Solute carrier family
Immune
- Acute phase protein
- Antibody
- Chemokines and their receptors
- Cytokines and their receptors
- MHC Class I
- MHC Class II
- Pattern recognition receptors
- Complement System
Genetic
- DNA/RNA synthesis
- DNA repair
- replication
- transcription (Transcription factor, transcriptional coregulator)
Signal transduction
Signal transduction
Sub-cellular distribution
thumb|475px|The human genome, categorized by the predicted [[Protein#Cellular localization|subcellular location distribution of each gene product.]]
Proteins may also be classified by which subcellular compartment they are found.
Nuclear
Nuclear proteins
Cytosolic
Cytosolic proteins
Cytoskeletal
Cytoskeletal proteins
Organelle
Endoplasmic reticulum
Endoplasmic reticulum resident protein
Lysosomal
Mitochondrial
Mitochondrial DNA that encode mitochondrial proteins (note that some mitochondrial proteins are encoded by nuclear DNA)
Chloroplast
Chloroplast DNA that encode chloroplast proteins
Cell membrane
Membrane protein
- Integral membrane protein
- Peripheral membrane protein
Extracellular matrix
Extracellular matrix proteins
Plasma
Blood protein
Species distribution
- Mammalian proteins
- Vertebrate proteins
- Plant proteins
- Bacterial proteins
- Archaeal proteins
- Viral proteins
<!-- ====Coagulation factors====
- Complement proteins
- C1-inhibitor
- C3-convertase
- Factor VIII
- Factor XIII
- Protein C
- Protein S
- Protein Z
- Protein Z-related protease inhibitor
- Thrombin
- Von Willebrand Factor
Acute phase proteins
- C-reactive protein
Hemoproteins
Hemoglobin (oxyhemoglobin and deoxyhemoglobin)
Cell adhesion
- Cadherin
- Ependymin
- Integrin
- NCAM
- Selectin
Transmembrane transport proteins
Ion pumping enzymes are in the enzymes section.
- CFTR
- Glycophorin D
- Scramblase
Ion channels
Ligand-gated ion channels
- Nicotinic acetylcholine receptor
- GABAa receptors
Voltage-gated ion channels
- Potassium channels
- Calcium channels
- Sodium channels
Synport / Antiport proteins
- Glucose transporter
Hormones and growth factors
Growth factors
- Colony-stimulating factors (CSFs)
- Epidermal growth factor (EGF)
- Fibroblast growth factor (FGF)
- Platelet-derived growth factor (PDGF)
- Transforming growth factors (TGFs)
- Vascular endothelial growth factor (VEGF)
Peptide hormones
- Insulin
- Insulin-like growth factor (IGF)
- Oxytocin
Receptors
- Receptors with enzyme activity are in the enzymes section.
- Receptors that are ion channels are in the ion channel section.
Transmembrane receptors
- G-protein-coupled receptor
- Rhodopsin
Intracellular receptors
- Estrogen receptor
DNA-binding protein
- Histones
- Protamines
Transcription & Regulation
- CI protein
Transcription regulatory proteins that are receptors are in the receptors section.
- C-myc
- FOXP2
- FOXP3
- MyoD
- P53
RNA-binding protein
- SRRT
Immune system proteins
- Immunoglobins
- Major histocompatibility antigens
- T cell receptor
Nutrient storage/transport
- Ferritin
Chaperone proteins
- GroEL
Enzymes
See List of enzymes
Complexes with multiple components including proteins
- Nucleosome
- Ribonucleoprotein (generic)
- Signal recognition particle
- Spliceosome -->
<!-- ==See also==
- Biology
- Enzymes
- Genes
- Proteins
- Index of protein-related articles
- List of enzymes
- NPW
- PEGylation
- Protein design Enzymes
- Protein family
- Structural domain -->