Filament-forming cytoskeletal proteins are key organizers of all cells. Bacterial homologs of the major eukaryotic cytoskeletal families have now been discovered, but studies suggest that yet more cytoskeletal proteins remain to be identified. Here we demonstrate that the metabolic enzyme CTP Synthase (CtpS) forms filaments in Caulobacter crescentus. These filaments are bifunctional and regulate Caulobacter curvature independently of CtpS catalytic activity. The morphogenic role of CtpS requires its functional interaction with the intermediate filament crescentin. Interestingly, the E. coli CtpS homolog also forms filaments both in vivo and in vitro, suggesting that CtpS polymerization may be widely conserved. E. coli CtpS can replace the enzymatic and morphogenic functions of Caulobacter CtpS, indicating that Caulobacter has adapted a conserved filament-forming protein for a secondary role. These results implicate CtpS as a novel bifunctional member of the bacterial cytoskeleton and suggest that localization and polymerization may be important properties of metabolic enzymes.

Cytoskeletal proteins are important mediators of cellular organization in both eukaryotes and bacteria. In the past, cytoskeletal studies have largely focused on three major cytoskeletal families, namely the eukaryotic actin, tubulin, and intermediate filament (IF) proteins and their bacterial homologs MreB, FtsZ, and crescentin. However, mounting evidence suggests that these proteins represent only the tip of the iceberg, as the cellular cytoskeletal network is far more complex. In bacteria, each of MreB, FtsZ, and crescentin represents only one member of large families of diverse homologs. There are also newly identified bacterial cytoskeletal proteins with no eukaryotic homologs, such as WACA proteins and bactofilins. Furthermore, there are universally conserved proteins, such as the metabolic enzyme CtpS, that assemble into filamentous structures that can be repurposed for structural cytoskeletal functions. Recent studies have also identified an increasing number of eukaryotic cytoskeletal proteins that are unrelated to actin, tubulin, and IFs, such that expanding our understanding of cytoskeletal proteins is advancing the understanding of the cell biology of all organisms. Here, we summarize the recent explosion in the identification of new members of the bacterial cytoskeleton and describe a hypothesis for the evolution of the cytoskeleton from self-assembling enzymes.

f you followed news headlines in the spring/summer of 2011, you may recognize E. coli as the agent responsible for outbreaks of serious diarrheal illness in Germany. But this is only one small part of the story of E. coli; its relationship to human health and the food we eat is much more complex. Not all E. coli are bad - in fact most are not - and some are even beneficial! In this report the larger story of E. coli is told: its role in human health, in food, and even in our understanding of our own biology.

SUMMARY➤ Properly designed point-of-care diagnostic tests can help to overcome health infrastructure deficiencies and lead to improved health care in resource-limited settings.➤ Scientific and technical advances can speed development of point-of-care tests, but they are only part of a far more complex process of developing tests that work effectively in particular settings.➤ Key characteristics that contribute to success in resource-limited settings should be included in the earliest design stages.➤ Developing point-of-care tests requires many stakeholders to communicate and collaborate effectively with one another. FEATURE ARTICLE