The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues earlier along the protein sequence.
The beta sheet, (β-sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet. A β-strand is a stretch of polypeptide chain typically 3 to 10 amino acids long with backbone in an extended conformation. The supramolecular association of β-sheets has been implicated in the formation of the fibrils and protein aggregates observed in amyloidosis, notably Alzheimer's disease.
The SRC Homology 3 Domain is a small protein domain of about 60 amino acid residues. Initially, SH3 was described as a conserved sequence in the viral adaptor protein v-Crk. This domain is also present in the molecules of phospholipase and several cytoplasmic tyrosine kinases such as Abl and Src. It has also been identified in several other protein families such as: PI3 Kinase, Ras GTPase-activating protein, CDC24 and cdc25. SH3 domains are found in proteins of signaling pathways regulating the cytoskeleton, the Ras protein, and the Src kinase and many others. The SH3 proteins interact with adaptor proteins and tyrosine kinases. Interacting with tyrosine kinases, SH3 proteins usually bind far away from the active site. Approximately 300 SH3 domains are found in proteins encoded in the human genome. In addition to that, the SH3 domain was responsible for controlling protein-protein interactions in the signal transduction pathways and regulating the interactions of proteins involved in the cytoplasmic signaling.
14-3-3 proteins are a family of conserved regulatory molecules that are expressed in all eukaryotic cells. 14-3-3 proteins have the ability to bind a multitude of functionally diverse signaling proteins, including kinases, phosphatases, and transmembrane receptors. More than 200 signaling proteins have been reported as 14-3-3 ligands.
In structural biology, a beta-propeller (β-propeller) is a type of all-β protein architecture characterized by 4 to 8 highly symmetrical blade-shaped beta sheets arranged toroidally around a central axis. Together the beta-sheets form a funnel-like active site.
An alpha solenoid is a protein fold composed of repeating alpha helix subunits, commonly helix-turn-helix motifs, arranged in antiparallel fashion to form a superhelix. Alpha solenoids are known for their flexibility and plasticity. Like beta propellers, alpha solenoids are a form of solenoid protein domain commonly found in the proteins comprising the nuclear pore complex. They are also common in membrane coat proteins known as coatomers, such as clathrin, and in regulatory proteins that form extensive protein-protein interactions with their binding partners. Examples of alpha solenoid structures binding RNA and lipids have also been described.
A leucine-rich repeat (LRR) is a protein structural motif that forms an α/β horseshoe fold. It is composed of repeating 20–30 amino acid stretches that are unusually rich in the hydrophobic amino acid leucine. These tandem repeats commonly fold together to form a solenoid protein domain, termed leucine-rich repeat domain. Typically, each repeat unit has beta strand-turn-alpha helix structure, and the assembled domain, composed of many such repeats, has a horseshoe shape with an interior parallel beta sheet and an exterior array of helices. One face of the beta sheet and one side of the helix array are exposed to solvent and are therefore dominated by hydrophilic residues. The region between the helices and sheets is the protein's hydrophobic core and is tightly sterically packed with leucine residues.
Receptor for activated C kinase 1 (RACK1), also known as guanine nucleotide-binding protein subunit beta-2-like 1 (GNB2L1), is a 35 kDa protein that in humans is encoded by the RACK1 gene.
Histidine kinases (HK) are multifunctional, and in non-animal kingdoms, typically transmembrane, proteins of the transferase class of enzymes that play a role in signal transduction across the cellular membrane. The vast majority of HKs are homodimers that exhibit autokinase, phosphotransfer, and phosphatase activity. HKs can act as cellular receptors for signaling molecules in a way analogous to tyrosine kinase receptors (RTK). Multifunctional receptor molecules such as HKs and RTKs typically have portions on the outside of the cell that bind to hormone- or growth factor-like molecules, portions that span the cell membrane, and portions within the cell that contain the enzymatic activity. In addition to kinase activity, the intracellular domains typically have regions that bind to a secondary effector molecule or complex of molecules that further propagate signal transduction within the cell. Distinct from other classes of protein kinases, HKs are usually parts of a two-component signal transduction mechanisms in which HK transfers a phosphate group from ATP to a histidine residue within the kinase, and then to an aspartate residue on the receiver domain of a response regulator protein. More recently, the widespread existence of protein histidine phosphorylation distinct from that of two-component histidine kinases has been recognised in human cells. In marked contrast to Ser, Thr and Tyr phosphorylation, the analysis of phosphorylated Histidine using standard biochemical and mass spectrometric approaches is much more challenging, and special procedures and separation techniques are required for their preservation alongside classical Ser, Thr and Tyr phosphorylation on proteins isolated from human cells.
The Sema domain is a structural domain of semaphorins, which are a large family of secreted and transmembrane proteins, some of which function as repellent signals during axon guidance. Sema domains also occur in the hepatocyte growth factor receptor, Plexin-A3 and in viral proteins.
Coronin is an actin binding protein which also interacts with microtubules and in some cell types is associated with phagocytosis. Coronin proteins are expressed in a large number of eukaryotic organisms from yeast to humans.
TSBP1 is a protein that in humans is encoded by the TSBP1 gene. C6orf10 is an open reading frame on chromosome 6 containing a protein that is ubiquitously expressed at low levels in the adult genome and may play a role during fetal development. C6orf10 has been found to be linked to both neurodegenerative and autoimmune diseases in adults. Expression of this gene is highest in the testis but is also seen in other tissue types such as the brain, lens of the eye and the medulla. TSBP1 was previously known as C6orf10.
The WD40 repeat is a short structural motif of approximately 40 amino acids, often terminating in a tryptophan-aspartic acid (W-D) dipeptide. Tandem copies of these repeats typically fold together to form a type of circular solenoid protein domain called the WD40 domain.
Cell surface receptors are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving extracellular molecules. They are specialized integral membrane proteins that allow communication between the cell and the extracellular space. The extracellular molecules may be hormones, neurotransmitters, cytokines, growth factors, cell adhesion molecules, or nutrients; they react with the receptor to induce changes in the metabolism and activity of a cell. In the process of signal transduction, ligand binding affects a cascading chemical change through the cell membrane.
The WW domain, is a modular protein domain that mediates specific interactions with protein ligands. This domain is found in a number of unrelated signaling and structural proteins and may be repeated up to four times in some proteins. Apart from binding preferentially to proteins that are proline-rich, with particular proline-motifs, [AP]-P-P-[AP]-Y, some WW domains bind to phosphoserine- phosphothreonine-containing motifs.
The Kelch motif is a region of protein sequence found widely in proteins from bacteria and eukaryotes. This sequence motif is composed of about 50 amino acid residues which form a structure of a four stranded beta-sheet "blade". This sequence motif is found in between five and eight tandem copies per protein which fold together to form a larger circular solenoid structure called a beta-propeller domain.
The CHASE domain is an extracellular protein domain, which is found in transmembrane receptor from bacteria, lower eukaryotes and plants. It has been named CHASE because of its presence in diverse receptor-like proteins with histidine kinase and nucleotide cyclase domains. The CHASE domain is 200-230 amino acids long and always occurs N-terminally in extracellular or periplasmic locations, followed by an intracellular tail housing diverse enzymatic signalling domains such as histidine kinase, adenyl cyclase, GGDEF-type nucleotide cyclase and EAL-type phosphodiesterase domains, as well as non-enzymatic domains such PAS, GAF, phosphohistidine and response regulatory domains. The CHASE domain is predicted to bind diverse low molecular weight ligands, such as the cytokinin-like adenine derivatives or peptides, and mediate signal transduction through the respective receptors.
In structural and cell biology, the focal adhesion targeting domain is a conserved protein domain that was first identified in focal adhesion kinase (FAK), also known as PTK2 protein tyrosine kinase 2 (PTK2).
In molecular biology, the HAMP domain is an approximately 50-amino acid alpha-helical region that forms a dimeric, four-helical coiled coil. It is found in bacterial sensor and chemotaxis proteins and in eukaryotic histidine kinases. The bacterial proteins are usually integral membrane proteins and part of a two-component signal transduction pathway. One or several copies of the HAMP domain can be found in association with other domains, such as the histidine kinase domain, the bacterial chemotaxis sensory transducer domain, the PAS repeat, the EAL domain, the GGDEF domain, the protein phosphatase 2C-like domain, the guanylate cyclase domain, or the response regulatory domain. In its most common setting, the HAMP domain transmits conformational changes in periplasmic ligand-binding domains to cytoplasmic signalling kinase and methyl-acceptor domains and thus regulates the phosphorylation or methylation activity of homodimeric receptors.
NHL Repeat Containing Protein 2, or NHLRC2, is a protein encoded by the NHLRC2 gene.
