Eukaryotes maintain an array of sub-cellular organelles to spatially organize and sequester DNA, RNA, and proteins. Despite their lack of membrane-bound organelles, bacteria have also developed mechanisms for protein localization and compartmentalization which are essential for a number of processes including chemotaxis, cell division, and adhesion (1-3). The importance of proper protein localization for organism viability highlights the need for investigating this fundamental process in prokaryotic cell biology. .
Our lab has chosen the gram-negative bacterium Caulobacter crescentus as a model organism for studying prokaryotic protein localization. To date, nearly all research on bacterial protein localization has been conducted with the goal of understanding the localization of one protein at a time. However, our lab has recently used a novel high-throughput microscopy method to annotate the localization of nearly all proteins in the C. crescentus proteome (4). Of the 3737 C. crescentus proteins, nearly 300 have distinct localization patterns. This "localisome " enables us to investigate global mechanisms of bacterial protein localization.
C. crescentus is one of several organisms that synthesize a tubular appendage, called a prosthecum or stalk. Additional stalk producing bacteria include Asticaccaulis biprosthecum, Hyphomonas neptunium, and Ancalomicrobium adetum (5). The stalk is hypothesized to function as a nutrient uptake antenna because it extends in response to low phosphate concentration (6) and contains a number of nutrient import proteins (7). The stalk is readily visible by light microscopy and is non-essential for viability allowing for greater use of genetic approaches. Furthermore, the C. crescentus localisome contains only 3 proteins which exclusively localize to the stalk: CC0498, CC1953, and CC3022 (4). This small subset of localized proteins provides an excellent starting point for studying mechanisms of bacterial protein localization and compartmentalization to a specific subcellular destination.