Catalytic proteins entries

Protein toxins acting intracellularly are often composed of two subunits (A/B model). One subunit is catalytic (A-subunit) and the other is responsible for binding and cell entry (B-subunit). Following binding to an extracellular membrane receptor, the toxins are endocytosed. From the endosomes, the A-subunit is directly (pH dqDendent) transferred into the cytosol (e.g., diphtheria toxin and anthrax toxin) or the toxin is transported in a retrograde manner via the golgi to the ER (e.g., cholera toxin), where translocation into the cytosol occurs [1]. 

The catalytic activities of the fortified wheat germ cell-free systems supplemented with each fraction were investigated (Fig. 2). As shown in Fig. 2, only 0 - 40 % ammonium sulfate fraction showed an enhancement in DHFR protein synthesis. This enhancement of protein experimental results and the fact that the various eukaryotic initiation factors are contained in synthesis was also confirmed by SDS-PAGE and autoradiography (Fig. 3). From the above 0-40 % ammonium sulfate fraction [5, 6], it can be concluded that the amount of initiation factors in a conventionally prepared wheat germ cell-fi extract is deficient for the translation of DHFR with internal ribosome entry site. Therefore, it needs to supplement a wheat germ cell-free extract with the fraction containing the limited initiation factors for the efficient protein translation, and this fortified cell-free system can be easily made by simple... 

Fig. 2. An example of a complex multidomain protein that includes both domain concatenation and intercalation. (A) See color insert. RASMOL view of phosphotransferase pyruvate kinase (pdb entry lpkn) colored to show the three identifiable domains. Blue is the j3 barrel regulatory domain, orange is an eightfold a/fi barrel, the catalytic substrate binding domain, and green is a central /3, a/(B nucleotide binding domain. Not displayed is the leader subsequence composed of a random coil and short helix. (B) Linear order along the sequence of these components.

A variety of domain or motif families occur only as extensions to other domains. The Bruton s tyrosine kinase motif (BTK), for example, is found only at the C terminus of PH domains. Similarly, a C-terminal extension (the S TK X domain) to some subfamilies of serine/threonine kinases (S TK) is not found in isolation. Cases where only the extension, and not the preceding domain, is found are strong evidence that the proteins are wrongly assembled from genomic sequence or else represent partial cDNA sequences (Fig. 9, see Color insert). Indeed, all five proteins annotated in SMART as containing a S TK X domain with no catalytic domain are noted to be fragments in their corresponding sequence database entries. 

In the PPA-a-AI 1 complex, a flexible loop of the enzyme, which would normally contact the substrate, is pushed outward to allow entry of the inhibitor, and one of the key aspartate residues is held in a conformation similar to that observed in the free enzyme. Therefore, some changes relative to the carbohydrate complex are required in order to accommodate the inhibitor. The structurally mimetic interactions within the catalytic site are supplemented by other specific protein-protein interactions, with a substantial buried surface area at the interface, involving 50 residues of the enzyme [171]. 

Selected entries from Methods in Enzymology [vol, page(s)] General Protein kinase classification, 200, 3 protein kinase catalytic domain sequence database identification of conserved features of primary structure and classification of family members,... 

Polyubiquitination of proteins requires ATP (Box 10-C) and additional ATP is utilized in the proteasomes (Box 7-A) during the selection of polyubiquitinated proteins for hydrolysis.447 448 With 28 subunits the 26S proteasome is complex and not fully understood 448 The ATP-hydrolyzing subunits appear to all be in the cap regions. Is the ATP used to open and close the entry pores To induce conformational changes in all subunits as part of a catalytic cycle Or to unfold folded proteins to help them enter the proteasomes 449... 

Index Entries Catalysts trace minerals protein catalytic hydrogenation hydrolysates. 

Each SWISS-PROT entry consists of general information about the entry (e.g., entry name and date, accession number), Name and origin of the protein (e.g., protein name, EC number and biological origin), References, Comments (e.g., catalytic activity, cofactor, subuit structure, subcellular location and family class, etc.), Cross-reference (EMBL, PIR, PDB, Pfam, ProSite, ProDom, ProtoMap, etc.), Keywords, Features (e.g., active site, binding site, modification, secondary structures, etc.), and Sequence information (amino acid sequence in Swiss-Prot format, Chapter 4). 

Because they are easily accessible, glycans displayed on the surface of mammalian cells provide enormous opportunities to bind to many microbial pathogens, ranging from viruses to molecular toxins and from pathogenic bacteria to parasites. In multivalent binding, multiple interactions between ligands and various receptors are common (Fig. 16.1). One representative example is ricin—a versatile and durable A-B-type toxin—in which one of the protein chains (the B chain) is a lectin that interacts and binds terminal galactose (Gal) on the surface of eukaryotic cells with multivalent interactions to facilitate entry of the other peptide chain (the A chain) into the cell to cause cellular death via the catalytic... 

Fig. 11.1 Relationship among catalytic intermediates of peroxidases. The formal oxidation state of each species is indicated by the numbers +2 to +6. The formal oxidation state of the species directly correlates with the relative energy content of the intermediates. The entry and exit of external electron donors/acceptors is indicated. In spite of its high oxidation state, Compound III is relative inert given the stability provided by the Fe(II) 02, Fe(III) 02 and Fe(IV) 022 resonance forms. Nevertheless, amino acid residues may rescue the free radical of Compound III, restore the iron atom ferric state, and allocate the free radical into a low redox potential site in the protein backbone. When the porphyrin performs as an electron donor, a different reaction occurs, resulting in tetrapyrrole bleaching and iron release...

Abrin exerts its toxic action in the same way as ricin. The abrin B-chain avidly binds to a variety of cell types, in particular reticuloendothehal cells which bear the appropriate mannose receptors. The abrin B-chain also binds to the galactosyl-terminated receptors on the cell membrane to allow the entry of the abrin A-chain. Once internalized, the abrin A-chain is transported from the cell membrane to the ribosomes, where it catalytically inactivates the 60S ribosomal subunit by removing adenine from positions 4 and 324 of 28S rRNA, thereby inhibiting protein synthesis and causing cell death (Stripe and Barbieri, 1986). 

How does the binding of cAMP activate the kinase Each R chain contains the sequence Arg-Arg-Gly-A/a-Ile, which matches the consensus sequence for phosphorylation except for the presence of alanine in place of serine. In the R2C2 complex, this pseudosubstrate sequence of R occupies the catalytic site of C, thereby preventing the entry of protein substrates (see Figure 10.28). The binding of cAMP to the R chains allosterically moves the pseudosubstrate sequences out of the catalytic sites. The released C chains are then free to bind and phosphorylate substrate proteins. 

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