CRP binding site

The overall direction of the reaction will be determined by the relative concentrations of ATP, ADP, Cr, and CrP and the equilibrium constant for the reaction. The enzyme can be considered to have two sites for substrate (or product) binding an adenine nucleotide site, where ATP or ADP binds, and a creatine site, where Cr or CrP is bound. In such a mechanism, ATP and ADP compete for binding at their unique site, while Cr and CrP compete at the specific Cr-, CrP-binding site. Note that no modified enzyme form (E ), such as an E-PO4 intermediate, appears here. The reaction is characterized by rapid and reversible binary ES complex formation, followed by addition of the remaining substrate, and the rate-determining reaction taking place within the ternary complex. 

The regulation of bacterial transcription is well illustrated by the lactose operon (lac operon) of the colon bacterium Escherichia coli in which the upstream region successively (from the 5 end of the sense strand) includes a promoter (P ) for the gene (I) coding for a repressor protein (the lac repressor), a CRP binding site , the promoter for the lac operon (P), and finally an operator site (O) that prefaces the Z, Y and A structural genes of the operon ... 

B) A mutation in the CRP binding site leading to enhanced binding... 

When the allosteric catabolite activator protein (CAP or CRP) binds cAMP, the dimeric protein is able to bind to a site in the promoter and to increase the rate of initiation of transcription... 

It should be noted that the presence of cross-links results in the partial or complete loss of control over the size of the polymer molecules, even if the living character of the polymerization can sometimes be preserved. Incidently, one of the characteristics of MIPs is that they are cross-linked polymers. This cross-linking is necessary in order to maintain the conformation of the three-dimensional binding sites obtained through the molecular imprinting process, and thus the ability of the polymer to recognize specifically and selectively its target molecule. Nevertheless, even with cross-linked polymers, the use of CRP methods may be beneficial, as it can, up to a certain point, improve the structure of the polymer matrix. Indeed, all of the above CRP methods have been applied to MIPs. 

Gronp 2 of the LIM domains contains the Cys-rich Proteins (CRP) and Cys-rich Intestinal Protein (CRIP) subfamilies that have tandem repeats of zinc-binding sites containing the ligands CCHC and CCCC (Table 6). The structures of the chicken, qnail, and rat 84 pj-Qteins are determined by NMR. These proteins have a role in the contractile machinery of mnscle. Three vertebrate CRPs (CRP 1-3) are associated with the actin cytoskeleton, and one has been shown to be reqnired for striated mnscle sttncture and function in mnscle differentiation and fimction. ... 

Group 2 of the LIM domains contains the Cys-rich Proteins (CRP) and Cys-rich Intestinal Protein (CRIP) subfamilies that have tandem repeats of zinc-binding sites containing the ligands CCHC and CCCC (Table 6). The structures of the chicken, quail,and proteins are determined... 

A cychc assembly can be considered as a cychc ohgomer formed by monomers either of the type A—B or of the type A—A + B—B as schematically shown in Fig. 10. The formation of a cyclic -mer requires n - 1 intermolecular bonds and one intramolecular bond. If all the n - 1 intermole-cular processes occur with the same constant JCinter> the stabihty constant of the supramolecular assembly is given by Eq. 13, where at and crp are statistical factors the former accounting for the number of equivalent binding sites of the reactants [cTr = 1 for the case (a), and = 2 for the case (b)],... 

Expression of the lac operon is regulated by controlling elements, which are separate from the structural genes. The controlling elements consist of a promoter locus, which is the site where RNA polymerase binds and initiates transcription the promoter locus also contains sites for the binding of a repressor and an activator. The i gene encodes the repressor, and the crp gene encodes the activator. 

All the DNA-binding proteins discussed thus far function by inhibiting transcription until some environmental condition, such as the presence of lactose, is met. There are also DNA-binding proteins that stimulate transcription. One particularly well studied example is the catabolite activator protein (CAP), which is also known as the cAMP response protein (CRP). When bound to cAMP, CAP, which also is a sequence-specific DNA-binding protein, stimulates the transcription of lactose- and arabinose-catabolizing genes. Within the lac operon, CAP binds to an inverted repeat that is centered near position -61 relative to the start site for transcription (Figure 31.10). CAP functions as a dimer of identical subunits. 

The short pentraxins were first described in the 1930s [203] and are the major components of a host of cytokine-induced liver proteins which mediate clearance of pathogens, known as acute phase proteins [200]. CRP shows 67-76% and SAP demonstrates 63-70% identical amino acids for the same protein in different species, while CRP and SAP share 42-54% identity in the same species [200]. Short pentraxins are conserved in vertebrates and are also present in unrelated organisms such as the horseshoe crab [202]. A number of biological functions have been proposed for CRP and SAP including complement activation, binding to sites of injury, activation of leukocytes, and association with amyloid fibrils [200]. 

Activated leukocytes induce the synthesis and secretion from the liver of an unrelated set of proteins called acute-phase proteins. One such protein, C-reactive protein (CRP) was originally identified as binding to the phosphocholine attachment site of capsular polysaccharide (C-polysaccharide) from Streptococcus pneumoniae. CRP in blood has a half life of less than a day, compared with 4 days for fibrinogen. A continuously elevated... 

Analysis of the DNA - protein complex shows that CRP induces DNA to bend quite sharply when it binds. This bending may facilitate the initiation of transcription by bringing DNA sequences farther upstream into direct contact with the promoter or transcriptional start site. 

Regulation - The araC gene encodes a regulatory protein that binds to arabinose, the inducer of the operon. Binding of the AraC - arabinose complex at a site called aral activates transcription of the arabinose operon, but only when the cAMP - CRP complex (see here) is bound at an adjacent site. Thus, whereas the lac operon requires one protein to be bound and one to be dissociated for maximal transcription, the arabinose operon requires two proteins to be bound at adjacent sites. 

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