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首页> 外文期刊>Infection and immunity >Reduction of enterotoxic activity of Escherichia coli heat-stable enterotoxin by substitution for an asparagine residue.
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Reduction of enterotoxic activity of Escherichia coli heat-stable enterotoxin by substitution for an asparagine residue.

机译：通过替换天冬酰胺残基降低大肠杆菌热稳定肠毒素的肠毒素活性。

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摘要

The Escherichia coli heat-stable enterotoxins (STs) are small peptide toxins consisting of 18 (STp) or 19 (STh) amino acids. STp and STh share biologically active sequences which reside in the C-terminal 13 amino acid residues, but the role of each amino acid in the active sequences is not clear. We substituted in vivo Asp, Tyr, His, Gln, Lys, and Arg for the Asn residue at position 11 of STp by oligonucleotide-directed site-specific mutagenesis and examined the biological activities of the resulting mutants. All mutant STs reacted with both monoclonal and polyclonal antibodies, demonstrating that the amino acid substitutions at position 11 did not cause a significant change in the conformation of STp. However, the substitutions invariably caused a significant decrease in enterotoxic activities. The most remarkable decrease was observed with Asn-11----Lys-11 and Asn-11----Arg-11 mutations; that is, enterotoxic activity could not be detected in the culture supernatant of either of these mutant strains. These results indicate that Asn-11 of STp plays an essential role in the enterotoxic activity. The amide group and the length of side chain of Asn-11 seem to be especially important for enterotoxic activity.
机译：大肠杆菌热稳定肠毒素（STs）是由18个（STp）或19个（STh）氨基酸组成的小肽毒素。 STp和STh共享位于C端13个氨基酸残基中的生物学活性序列，但是尚不清楚每个氨基酸在活性序列中的作用。通过寡核苷酸定向位点特异性诱变，我们在体内用Asp，Tyr，His，Gln，Lys和Arg取代了STp 11位的Asn残基，并检查了所得突变体的生物学活性。所有突变体ST均与单克隆抗体和多克隆抗体反应，表明在11位的氨基酸取代不会引起STp构象的显着变化。然而，这些取代总是导致肠毒性活性的显着降低。 Asn-11 ---- Lys-11和Asn-11 ---- Arg-11突变最明显。即，在这两个突变株的培养上清液中均未检测到肠毒活性。这些结果表明STp的Asn-11在肠毒性活性中起重要作用。 Asn-11的酰胺基和侧链长度似乎对肠毒性活性特别重要。

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