Bacterial protein toxins with latent ADP-ribosyl transferases activities

Community-Acquired Respiratory Distress Syndrome Toxin: Unique Exotoxin for M. pneumoniae

Mycoplasma pneumoniae infection often causes respiratory diseases in humans, particularly in children and adults with atypical pneumonia and community-acquired pneumonia (CAP), and is often exacerbated by co-infection with other lung diseases, such as asthma, bronchitis, and chronic obstructive pulmonary disorder. Community-acquired respiratory distress syndrome toxin (CARDS TX) is the only exotoxin produced by M. pneumoniae and has been extensively studied for its ADP-ribosyltransferase (ADPRT) activity and cellular vacuolization properties. Additionally, CARDS TX induces inflammatory responses, resulting in cell swelling, nuclear lysis, mucus proliferation, and cell vacuolization. CARDS TX enters host cells by binding to the host receptor and is then reverse transported to the endoplasmic reticulum to exert its pathogenic effects. In this review, we focus on the structural characteristics, functional activity, distribution and receptors, mechanism of cell entry, and inflammatory response of CARDS TX was examined. Overall, the findings of this review provide a theoretical basis for further investigation of the mechanism of M. pneumoniae infection and the development of clinical diagnosis and vaccines.

Some properties of purified Escherichia coli heat-stable enterotoxin II

We examined the biological properties of purified Escherichia coli heat-stable enterotoxin II (STII) using mouse intestinal loop assays and compared these properties with those of heat-stable enterotoxin I (STI) and cholera toxin (CT). The action of STII over time differed from those of STI and CT. STII did not alter cyclic GMP or cyclic AMP levels in intestinal mucosal cells. Our results supported the idea that the mechanism of action of STII in inducing fluid secretion is different from the mechanisms of action of STI and CT. This hypothesis was further supported by the fact that an anti-STII neutralizing serum did not neutralize the activities of STI and CT. Subsequently, we examined the involvement of prostaglandins in the action of STII. The level of prostaglandin E2 in the fluid accumulated as a result of the action of STII increased, and the prostaglandin synthesis inhibitors aspirin and indomethacin significantly reduced the response to STII. These results implicate prostaglandin E2 in the mechanism of action of STII.

Effect of substitution of glycine for arginine at position 146 of the A1 subunit on biological activity of Escherichia coli heat-labile enterotoxin

The ADP-ribosyltransferase activity of polypeptide A1 of cholera toxin and that of Escherichia coli heat-labile enterotoxin (LT) are primarily responsible for the toxic activities of these toxins. Since the amino acid sequences of the two A1 polypeptides are very similar, their functional mechanisms are considered to be the same. Arg-146 of polypeptide A1 is thought to be involved in the active site, because this amino acid of cholera toxin has been identified as the site of self-ADP-ribosylation. However, the exact role of Arg-146 and the significance of self-ADP-ribosylation in toxicity remain unclear. We substituted Arg-146 of polypeptide A1 of LT with Gly by oligonucleotide-directed mutagenesis and examined the biological property of the resultant mutant LT. The substitution changed the mobility of subunit A on sodium dodecyl sulfate-polyacrylamide gel but did not reduce the vascular permeability activity of LT. This result indicates that Arg-146 is not absolutely required for toxic activity and that LT can express its toxic activity without self-ADP-ribosylation at Arg-146.

Photolabelling of cholera toxin by NAD+

When cholera toxin is incubated under u.v. light with NAD+ labelled in either the adenine or the nicotinamide moiety, radioactivity becomes covalently bound to the protein. The reaction is specific for cholera toxin, and is inhibited by excess unlabelled NAD+ or NAD analogues. Only the active A 1 chain of the toxin is labelled. The u.v.-absorption spectrum of the product is very similar to that of NAD+, and shows the same reaction with cyanide. The nature of the product is therefore different from that found when diphtheria toxin is photolabelled [Carroll & Collier (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3307-3311] in that the yield is lower, but both moieties of the NAD molecule become bound.