Universal stress proteins in Escherichia coli have both distinct and overlapping functions in oxidative stress resistance, adhesion and motility.
Several previously unknown functions of the universal stress protein A (UspA) family in Escherichia coli have been revealed by a new functional genomic analysis recently published in the Journal of Bacteriology.
It had previously been observed that the E. coli UspA proteins undergo coordinated induction in response to various stresses, but there was little information on the functions of individual UspAs. There are six E. coli UspA proteins, and they can be divided into four classes based on structural motifs — three proteins (UspA, UspC and UspD) belong to class I, two to class II (UspF and UspG) and the sixth protein, UspE, belongs to both classes III and IV. Laurence Nachin, Ulf Nannmark and Thomas Nyström used this information to create a series of chromosomal deletion mutants designed to analyse the functions of members of each class.
Analysis of growth in the presence of phenazine methosulphate revealed that two of the three class I proteins, UspA and UspD, are involved in defence against oxidative stress. In addition, the uspD mutant showed the greatest sensitivity to the addition of streptonigrin, an antibiotic with iron-dependent activity, indicating a role for this class I protein in intracellular iron scavenging. Neither of these functions had previously been attributed to UspA proteins. A serendipitous observation revealed another previously unknown function — the authors noticed that the different mutant cultures had different flocculation profiles, with cell–cell aggregation greatly reduced in uspC and uspE cultures, indicating that these proteins might be involved in regulating adhesion capabilities.
The ability of the different mutant cultures to form fimbriae was then assessed using a yeast agglutination assay. Agglutination was enhanced in uspC and uspE cells and reduced in uspF and uspG cells. As adhesion and motility often show reciprocal regulation, motility was then examined in a swimming assay, and was found to be decreased in uspC and uspE mutants and increased in uspF and uspG mutants. Further analysis revealed that uspC and uspE cells lack flagella. Therefore, the authors note that, in addition to their other newly identified roles, UspA proteins are also involved in "reprogramming the cell towards defense and escape".
This study highlights the power of functional genomics and shows that the extensively studied model organism E. coli still holds some surprises. Contrary to expectation, the UspA proteins have distinct, as well as overlapping, functions, and some might be involved in controlling a bacterial version of the 'fight or flight' response.
Sheilagh Molloy
References
Nachin, L., Nannmark, U. & Nyström, T. Differential roles of the universal stress proteins of Escherichia coli in oxidative stress resistance, adhesion and motility. J. Bacteriol.187, 6265–6272 (2005) | Article | PubMed |
uspD mutant showed the greatest sensitivity to the addition of streptonigrin, an antibiotic with iron-dependent activity, indicating a role for this class I protein in intracellular iron scavenging. Neither of these functions had previously been attributed to UspA proteins. A serendipitous observation revealed another previously unknown function — the authors noticed that the different mutant cultures had different flocculation profiles, with cell–cell aggregation greatly reduced in 