Ph.D. Biochemistry, Molecular and Cell Biology, Johns Hopkins University School of Medicine, 1997
A.B. History of Science, Harvard College, 1990
The Ryan lab studies mechanisms such as phosphorylation, localization, and proteolysis that regulate protein activity in bacteria. Our model system is the Gram-negative freshwater bacterium Caulobacter crescentus, in which post-translational regulation plays an important role in cell cycle transitions and the differentiation of one cell type into another. Ongoing projects in the lab include investigation of 1) proteolysis of the cell cycle regulator CtrA, 2) the role of serine/threonine/tyrosine phosphorylation in regulating Caulobacter physiology, and 3) the functions of PBP1a enzymes in Caulobacter cell wall integrity and morphology.
Cell cycle control and asymmetric cell division in the gram negative bacterium Caulobacter crescentus
In the not-too-distant past, bacteria were thought to be relatively simple organisms, constantly engaged in DNA replication and binary fission, with cytosolic components distributed at random throughout the cell. We now know that bacterial cells can have complex life cycles and highly organized interior architectures. Bacteria contain cytoskeletal elements that influence their shape and mediate cell division. They place large macromolecular assemblies, such as flagella, stalks, and pili, at specific sites on the cell surface. GFP fusion proteins have revealed that individual signal transduction proteins can have subcellular addresses, and they can move as a function of the cell cycle or developmental status of the bacterium. I want to understand how spatial cues, such as protein localization, and temporal events, such as protein activation or degradation, are controlled and combined to produce an orderly bacterial cell cycle.
The gram negative bacterium Caulobacter crescentus is an ideal organism in which to ask these questions, because its cell cycle is easily studied, and every cell division is asymmetric, resulting in two progeny with different morphologies, protein complements, and replicative fates. The life cycle of Caulobacter begins with the motile swarmer cell (SW), which cannot replicate its chromosome or undergo cell division. The swarmer cell differentiates into a stalked cell (ST), shedding its flagellum and building a stalk at the same site. During this transition, the cell gains the ability to initiate DNA replication and enter the division cycle. The stalked cell grows into an asymmetric predivisional cell (PD), with a new flagellum at the pole opposite the stalk. Every cell division produces a swarmer cell and a stalked cell. The stalked cell can immediately begin a new round of chromosome replication and cell division, while the swarmer cell must first differentiate into a stalked cell.
Caulobacter life cycle
We can isolate pure populations of swarmer cells and observe many parameters during their synchronous progress through the cell cycle, including fluorescent protein localization, DNA content, and global transcriptional patterns. The Caulobacter genome has been sequenced, which expedites genetic manipulations and allows us to search comprehensively for genes that affect processes of interest. We pursue complementary in vitro studies to determine how the biochemical properties of individual regulatory proteins contribute to cell cycle progression and cellular asymmetry.
Please see the Ryan lab web site for more information about ongoing research: http://kathleenryanlab.berkeley.edu/
Taylor JA, Wilbur JD, Smith SC, and Ryan KR. Mutations that alter RcdA surface residues decouple protein localization and CtrA proteolysis in Caulobacter crescentus. J. Mol. Biol. 2009 394: 46-60.
Reisinger SJ, Huntwork S, Viollier PH, and Ryan KR. DivL performs critical cell cycle functions in Caulobacter crescentus independent of kinase activity. J. Bacteriol. 2007 189: 8308-8320.
Biondi EG, Reisinger SJ, Skerker JM, Arif M, Perchuk BS, Ryan KR, and Laub MT. Regulation of the bacterial cell cycle by an integrated genetic circuit. Nature. 2006 444: 899-904.
McGrath PT, Iniesta AA, Ryan KR, Shapiro L, McAdams HH. A dynamically localized protease complex and a polar specificity factor control a cell cycle master regulator. Cell. 2006 Feb 10;124(3):535-47.
Ryan KR. Partners in crime: phosphotransfer profiling identifies a multicomponent phosphorelay. Mol Microbiol. 2006 Jan;59(2):361-3.
Ryan KR, Huntwork S, Shapiro L. Recruitment of a cytoplasmic response regulator to the cell pole is linked to its cell cycle-regulated proteolysis. Proc Natl Acad Sci U S A. 2004 May 11;101(19):7415-20. Epub 2004 Apr 29.
Judd, E.M., Ryan, K.R., Moerner, W.E., Shapiro, L. and McAdams, H.H. Fluorescence bleaching reveals asymmetric compartment formation prior to cell division in Caulobacter. PNAS 2003 USA 100: 8235-8240.
Ryan, K.R. and Shapiro, L. Temporal and spatial regulation in prokaryotic cell cycle progression and development. Annu. Rev. Biochem. 2003 72: 367-394.
Ryan, K.R., Judd, E.M. and Shapiro, L. The CtrA response regulator essential for Caulobacter crescentus cell cycle progression requires a bipartite degradation signal for temporally controlled proteolysis. J. Mol. Biol. 2002 324: 443-455.
Hellman Family Faculty Fund Award - 2008
Regents' Junior Faculty Fellowship - UC Regents - 2007
College of Natural Resources Distinguished Teaching Award - 2007