Structure Pertussis toxin

GM-CSF and IL-3 have been shown to compete for receptors in some types of cells (e.g. eosinophils and KG-1 cells), indicating some structural homology between GM-CSF and IL-3 receptors, perhaps because they share certain subunits or adapter proteins. GM-CSF occupancy results in phosphorylation of certain proteins, and because the receptor possesses no inherent kinase activity, receptor occupancy must be linked to kinase activity via the generation of second messenger molecules. Pretreatment of cells with pertussis toxin abolishes the effects of GM-CSF, indicating the involvement of G-proteins in signal transduction. Priming of neutrophil functions with GM-CSF involves the activation of phospholipases A2 and D. 

All of these experimental approaches have been adopted in neutrophil studies to show that activation of several receptor-mediated functions occurs via the participation of heterotrimeric G-proteins. In many cases, the conventional Gai/Gas nomenclature is used to describe these G-proteins, even though the subunits may not be linked to either inhibition or activation of adenylate cyclase. The nomenclature used is based on structural and functional similarities to other Ga-subunits in other cell types, and also on their sensitivities to cholera and pertussis toxins. Several of these G-proteins... 

Burns DL. Subunit structure and enzymic activity of pertussis toxin. Microbiol. Sci. 1988 5 285-287. 

Based on the functional similarities between the pertussis toxin and the selectins (including their ability to bind to similar sialic acid-containing oligosaccharides structures), Rozdzinski et al. [166] and Heerze et al. [169] synthesized peptides from the regions of sequence similarity in an effort to find molecules that adhere to sialic acid-containing glycoconjugates. The recombinant subunits S2 and S3 of pertussis toxin and the synthetic peptides competitively inhibited adherence of neutrophils to selectin-coated surfaces and to endothelial cells in vitro. 

There is another large class of receptors whose occupancy by an agonisf leads to inhibition of adenylate cyclase. These include the tt2 adrenergic receptors, receptors for acetylcholine, adenosine, prostaglandin E2 (Chapter 21), somatostatin, and some receptors for dopamine. Their responses are mediafed by inhibitory proteins Gj, which closely resemble Gg in their sizes, amino acid sequences, and heterotrimeric structures, but which inhibit adenylate cyclase when activated. A clear distinction between the Gg and Gj proteins is evident in the fact that Gg is irreversibly activated by the action of cholera toxin, while G loses its ability to respond to occupied receptors when modified by the action of Pertussis toxin (Box 11-A). A specialized heterotrimeric G protein known as transducin mediates the light-induced activation of a cyclic GMP phosphodiesterase in the retina " (see Chapter 23). Its a subunit is designated aj. The related gustducin is found in taste buds. ... 

Kaslow HR, Urn LK, Moss J, et al. (1987) Structure-activity analysis of the activation of pertussis toxin. In Biochemistry 26 123-127. 

Nicosia A, Perugini M, Franzini C, etal. (1986) Cloning and sequencing of the pertussis toxin gene operon structure and gene duplication. In Proc. Natl. Acad. Sci. USA 83 4631 -4635. 

Stein PE, Boodhoo A, Armstrong GD, et al. (1994a) The crystal structure of pertussis toxin. In Structure 2 45—57. 

Tamura M, Nogimori K, Murai S, et a/. (1982) Subunit structure of islet-activating protein, pertussis toxin, in conformity with the A-B model. In Biochemistry 21 5516-5522. 

The recent solution of the crystal structure of a dimeric form of pertussis toxin provided support for the composite nature of the molecule [124]. Thus, the WGA-like region of S2 superimposes on the homologous part of the three-dimensional structure of WGA (residues 62-67), while the segment homologous to the C-type lectins superimposes on the core of rat mannose binding protein, a C-type lectin. 

A second CXCR3 variant has also been identified that is truncated at the C-terminus (CXCR3-alt, [6]). This altered receptor has a predicted four or five-transmembrane structure lacking the third and most of the second extracellular loop. In spite of the truncated form of CXCR3-alt, this variant was able to transduce a chemotactic signal by CXCL11 that was sensitive to inhibition by pertussis toxin. 

Pertussis toxin consists of five subunits, SI to S5. The SI subunit (or A pro-tomer) is responsible for the ADP-ribosyltransferase activity and also possesses NAD glycohydrolase activity (111). Cysteine has been identified as the amino acid residue in transducin that is ADP-ribosylated by the toxin (110) recently thiols such as cysteine and dithiothreitol have been reported to be ADP-ribosylated by pertussis toxin (//V). No data on the stereochemistry of this linkage are available. Several groups are attempting to characterize the structure of the SI subunit (124, 125) and to identify the amino acid residues essential for enzymic activity (126, 127). Interestingly, there is a sequence identity in a portion of the active subunits of cholera and pertussis toxins, and antibodies raised to residues... 

The TS structures initially reported for the cholera and pertussis toxin-catalyzed hydrolysis reactions had leaving group bond orders, /Ilg. of 0.09 and 0.1, respectively, and very low nucleophile bond orders, /Inu. of 0.005 and 0.001. It was later shown using structure interpolation that it is necessary to account for increases in the N1-C2 and N1-C6 bond orders in the nicotinamide ring that partially compensate for the loss of Cl -Nl bond order. After accounting for changes in the nicotinamide ring structure, the TS structures were essentially the same as for DTA, which had and nu = 0.03. It should be emphasized... 

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