In biology and biochemistry, protease inhibitors, or antiproteases, are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins.
Diphtheria toxin is an exotoxin secreted mainly by Corynebacterium diphtheriae but also by Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. the pathogenic bacterium that causes diphtheria. The toxin gene is encoded by a prophage called corynephage β. The toxin causes the disease in humans by gaining entry into the cell cytoplasm and inhibiting protein synthesis.
Salmonella virus P22 is a bacteriophage in the Podoviridae family that infects Salmonella typhimurium. Like many phages, it has been used in molecular biology to induce mutations in cultured bacteria and to introduce foreign genetic material. P22 has been used in generalized transduction and is an important tool for investigating Salmonella genetics.
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.
Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis of carbamoyl phosphate from glutamine or ammonia and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP. Carboxy phosphate reacts with ammonia to give carbamic acid. In turn, carbamic acid reacts with a second ATP to give carbamoyl phosphate plus ADP.
Formins (formin homology proteins) are a group of proteins that are involved in the polymerization of actin and associate with the fast-growing end (barbed end) of actin filaments. Most formins are Rho-GTPase effector proteins. Formins regulate the actin and microtubule cytoskeleton and are involved in various cellular functions such as cell polarity, cytokinesis, cell migration and SRF transcriptional activity. Formins are multidomain proteins that interact with diverse signalling molecules and cytoskeletal proteins, although some formins have been assigned functions within the nucleus.
Cullins are a family of hydrophobic scaffold proteins which provide support for ubiquitin ligases (E3). All eukaryotes appear to have cullins. They combine with RING proteins to form Cullin-RING ubiquitin ligases (CRLs) that are highly diverse and play a role in myriad cellular processes, most notably protein degradation by ubiquitination.
The L27 domain is a protein domain that is found in receptor targeting proteins Lin-2 and Lin-7, as well as some protein kinases and human MPP2 protein. The L27 domain is a protein interaction module that exists in a large family of scaffold proteins, functioning as an organisation centre of large protein assemblies required for the establishment and maintenance of cell polarity. L27 domains form specific heterotetrameric complexes, in which each domain contains three alpha-helices. The L27_2 domain is a protein-protein interaction domain capable of organising scaffold proteins into supramolecular assemblies by formation of heteromeric L27_2 domain complexes. L27_2 domain-mediated protein assemblies have been shown to play essential roles in cellular processes including asymmetric cell division, establishment and maintenance of cell polarity, and clustering of receptors and ion channels. Members of this family form specific heterotetrameric complexes, in which each domain contains three alpha-helices. The two N-terminal helices of each L27_2 domain pack together to form a tight, four-helix bundle in the heterodimer, whilst the third helix of each L27_2 domain forms another four-helix bundle that assembles the two units of the heterodimer into a tetramer.
In molecular biology, chaperone DnaJ, also known as Hsp40, is a molecular chaperone protein. It is expressed in a wide variety of organisms from bacteria to humans.
In molecular biology, the myogenic determination factor 5 proteins are a family of proteins found in eukaryotes. This family includes the Myf5 protein, which is responsible for directing cells to the skeletal myocyte lineage during development. Myf5 is likely to act in a similar way to the other MRF4 proteins such as MyoD which perform the same function. These are histone acetyltransferases and histone deacetylases which activate and repress genes involved in the myocyte lineage.
In molecular biology, the Cbl TKB domain, also known as the phosphotyrosine binding (PTB) domain is a conserved region found at the N-terminus of Cbl adaptor proteins. This N-terminal region is composed of three evolutionarily conserved domains: an N-terminal four-helix bundle domain, an EF hand-like domain and a SH2-like domain, which together are known to bind to phosphorylated tyrosine residues.
In molecular biology, a carbohydrate-binding module (CBM) is a protein domain found in carbohydrate-active enzymes. The majority of these domains have carbohydrate-binding activity. Some of these domains are found on cellulosomal scaffoldin proteins. CBMs were previously known as cellulose-binding domains. CBMs are classified into numerous families, based on amino acid sequence similarity. There are currently 64 families of CBM in the CAZy database.
In molecular biology, the CDC48 N-terminal domain is a protein domain found in AAA ATPases including cell division protein 48 (CDC48), VCP-like ATPase and N-ethylmaleimide sensitive fusion protein. It is a substrate recognition domain which binds polypeptides, prevents protein aggregation, and catalyses refolding of permissive substrates. It is composed of two equally sized subdomains. The amino-terminal subdomain (CDC48_N) forms a double-psi beta-barrel whose pseudo-twofold symmetry is mirrored by an internal sequence repeat of 42 residues. The carboxy-terminal subdomain (CDC48_2) forms a novel six-stranded beta-clam fold. Together these subdomains form a kidney-shaped structure, in close agreement with results from electron microscopy. CDC48_N is related to numerous proteins including prokaryotic transcription factors, metabolic enzymes, the protease cofactors UFD1 and PrlF, and aspartic proteinases.
In molecular biology, the cohesin domain is a protein domain. It interacts with a complementary domain, termed the dockerin domain. The cohesin-dockerin interaction is the crucial interaction for complex formation in the cellulosome.
In molecular biology, the Cro repressor family is a family of repressor proteins in bacteriophage lambda that includes the Cro repressor.
In molecular biology, multicopper oxidases are enzymes which oxidise their substrate by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear copper centre; dioxygen binds to the trinuclear centre and, following the transfer of four electrons, is reduced to two molecules of water. There are three spectroscopically different copper centres found in multicopper oxidases: type 1, type 2 and type 3. Multicopper oxidases consist of 2, 3 or 6 of these homologous domains, which also share homology with the cupredoxins azurin and plastocyanin. Structurally, these domains consist of a cupredoxin-like fold, a beta-sandwich consisting of 7 strands in 2 beta-sheets, arranged in a Greek-key beta-barrel. Multicopper oxidases include:
In molecular biology, excisionase is a bacteriophage protein encoded by the Xis gene. It is involved in excisive recombination by regulating the assembly of the excisive intasome and by inhibiting viral integration. It adopts an unusual winged-helix structure in which two alpha helices are packed against two extended strands. Also present in the structure is a two-stranded anti-parallel beta-sheet, whose strands are connected by a four-residue wing. During interaction with DNA, helix alpha2 is thought to insert into the major groove, while the wing contacts the adjacent minor groove or phosphodiester backbone. The C-terminal region of excisionase is involved in interaction with phage-encoded integrase (Int), and a putative C-terminal alpha helix may fold upon interaction with Int and/or DNA.
In molecular biology the FGGY carbohydrate kinase family is a family of evolutionarily related carbohydrate kinase enzymes. These enzymes include L-fuculokinase EC 2.7.1.51 ; gluconokinase EC 2.7.1.12 ; glycerol kinase EC 2.7.1.30 ; xylulokinase EC 2.7.1.17 ; D-ribulose kinase EC 2.7.1.47 ; and L-xylulose kinase EC 2.7.1.53. These enzymes are proteins of from 480 to 520 amino acid residues.
In molecular biology, a phage major coat protein is an alpha-helical protein that forms a viral envelope of filamentous bacteriophages. These bacteriophages are flexible rods, about one to two micrometres long and six nm in diameter, with a helical shell of protein subunits surrounding a DNA core. The approximately 50-residue subunit of the major coat protein is largely alpha-helix, and the axis of the alpha-helix makes a small angle with the axis of the virion. The protein shell can be considered in three sections: the outer surface, occupied by the N-terminal region of the subunit and rich in acidic residues that give the virion a low isoelectric point; the interior of the shell where protein subunits interact, mainly with each other; and the inner surface, rich in positively charged residues that interact with the DNA core.
In molecular biology, the YqaJ refers to the YqaJ/K domain from the skin prophage of the bacterium, Bacillus subtilis. This protein domain, often found in bacterial species, is actually of viral origin. The protein forms an oligomer and functions as an alkaline exonuclease, or in simpler terms, an enzyme that digests double-stranded DNA. It is a reaction which is dependent on Magnesium. It has a preference for 5'-phosphorylated DNA ends. It thus forms part of the two-component SynExo viral recombinase functional unit.
