Address

Hwan Youn Lab

Hwan Youn

Assistant Professor

Degree

Ph.D., 1998, Seoul National University

Postdoctoral Research

University of Wisconsin-Madison

Address

Department of Biology

College of Science & Mathematics

California State University, Fresno

2555 E. San Ramon Ave. M/S SB73

Fresno, CA 93740-8034

Phone: 1-559-278-8305

Fax: 1-559-278-3963

E-mail: hyoun@csufresno.edu

Office/ lab: S202A/ S202

My Research

Bacteria are everywhere on earth. Their omnipresence is due to their adaptation to environmental cues, which relies on specialized sensing mechanisms for environmental changes. The CooA/CRP/FNR family of transcription factors sense all kinds of ligands, including oxygen, carbon monoxide, nitric oxide, and metabolites like a-ketoglutarate and aromatic compounds, thereby helping bacteria express specific genes necessary for environmental/ nutritional changes. The structural motif for this versatile CooA/CRP/FNR family is rather simple: each member has two domains (N-terminal ligand-binding domain and C-terminal DNA-binding domain) connected by a long C-helix component. These proteins act as dimers.

My recent work has focused on two members of this family: CooA and CRP. CooA is the CO (carbon monoxide)-dependent, heme-containing transcriptional activator in Rhodospirillum rubrum. CRP is the cAMP receptor protein that senses the absence of a particular carbon source, glucose, in Escherichia coli by responding to the intracellular level of cAMP, thereby regulating the expression of carbon metabolism-related genes. My scientific question has been how the conformations of these proteins are changed by ligand binding in the context of DNA binding and what are the critical components in the signaling pathway for each protein.

Interestingly, some of the proteins of this family are known to function as virulence factors in human pathogens such as Listeria monocytogens, Pseudomonas aeruginosa, and others. Many critical details are yet to be learned such as their cognate ligands and their cellular targets for regulation. My intention is to apply current knowledge of CooA/CRP/FNR protein family to the homologs in the pathogens in order to understand their role during the process of pathogenesis.

Publications

30. Serate J, Roberts GP, Berg O, Youn H (2011) Ligand responses of Vfr, the virulence factor regulator from Pseudomonas aeruginosa. J. Bacteriol. 193:4859-4868.

29. Lee AJ, Clark RW, Youn H, Ponter S, Burstyn JN (2009) Guanidine hydrochloride-induced unfolding of the three heme coordination states of the CO-sensing transcription factor, CooA. Biochemistry 48:6585-6597.

28. Marvin KA, Kerby RL, Youn H, Roberts GP, Burstyn JN (2008) The Transcription Regulator RcoM-2 from Burkholderia xenovorans Is a Cysteine-Ligated Hemoprotein That Undergoes a Redox-Mediated Ligand Switch. Biochemistry 47:9016-9028.

27. Youn H, Koh J, Roberts GP (2008) Two-state allosteric modeling suggests protein equilibrium as an integral component for cyclic AMP (cAMP) specificity in the cAMP receptor protein of Escherichia coli. J. Bacteriol. 190:4532-4540.

26. Kerby RL, Youn H, Roberts GP (2008) RcoM: a new single-component transcriptional regulator of CO metabolism in bacteria. J. Bacteriol. 190:3336-3343.

25. Ibrahim M, Kuchinskas M, Youn H, Kerby RL, Roberts GP, Poulos TL, Spiro TG (2007) Mechanism of the CO-sensing heme protein CooA: New insights from the truncated heme domain and UVRR spectroscopy. J. Inorg. Biochem. 101:1776-1785.

24. Youn H, Kerby RL, Koh J and Roberts GP (2007) A C-helix residue, Arg123, has important roles in both the active and inactive forms of the cAMP receptor protein. J. Biol. Chem. 282:3632-3639.

23. Clark RW, Youn H, Lee AJ, Roberts GP and Burstyn JN (2007) DNA binding by an imidazole-sensing CooA variant is dependent on the heme redox state. J. Biol. Inorg. Chem. 12:139-146.

22. Youn H, Conrad M, Chung SY and Roberts GP (2006) Roles of the heme and heme ligands in the activation of CooA, the CO-sensing transcriptional activator. Biochem. Biophys Res. Commun. 348:345-350.

21. Ibrahim M, Kerby RL, Puranik M, Wasbotten IH, Youn H, Roberts GP and Spiro TG (2006) Heme displacement mechanism of CooA activation: mutational and Raman spectroscopic evidence. J. Biol. Chem. 281:29165-29173.

20. Youn H, Kerby RL, Conrad M and Roberts GP (2006) Study of highly constitutively active mutants suggests how cAMP activates cAMP receptor protein. J. Biol. Chem. 281:1119-1127.

19. Youn H, Thorsteinsson MV, Conrad M, Kerby RL and Roberts GP (2005) Dual roles of an E-helix residue, Glu167, in the transcriptional activator function of CooA. J. Bacteriol. 187:2573-2581.

18. Roberts GP, Kerby RL, Youn H and Conrad M (2005) CooA, a paradigm for gas sensing regulatory proteins. J. Inorg. Biochem. 99:280-292.

17. Clark RW, Youn H, Parks RB, Cherney MM, Roberts GP and Burstyn JN (2004) Investigation of the role of the N-terminal proline, the distal heme ligand in the CO sensor CooA. Biochemistry 43:14149-14160.

16. Roberts GP, Youn H and Kerby RL (2004) CO-sensing mechanisms. Microbiol. Mol. Biol. Rev. 68:453-473.

15. Youn H, Kerby RL and Roberts GP (2004) Changing the ligand specificity of CooA, a highly specific heme-based CO sensor. J. Biol. Chem. 279:45744-45752.

14. Puranik M, Nielsen SB, Youn H, Hvitved AN, Bourassa JL, Case MA, Tengroth C, Balakrishnan G, Thorsteinsson MV, Groves JT, McLendon GL, Roberts GP, Olson JS and Spiro TG (2004) Dynamics of carbon monoxide binding to CooA. J. Biol. Chem. 279:21096-21108.

13. Youn H, Kerby RL, Conrad M and Roberts GP (2004) Functionally critical elements of CooA-related CO sensors. J. Bacteriol. 186:1320-1329.

12. Coyle CM, Puranik M, Youn H, Nielsen SB, Williams RD, Kerby RL, Roberts GP and Spiro TG (2003) Activation mechanism of the CO sensor CooA. Mutational and resonance Raman spectroscopic studies. J. Biol. Chem. 278:35384-35393.

11. Kerby RL, Youn H, Thorsteinsson MV and Roberts GP (2003) Repositioning about the dimer interface of the transcription regulator CooA: a major signal transduction pathway between the effector and DNA-binding domains. J. Mol. Biol. 325:809-823.

10. Youn H, Kerby RL and Roberts GP (2003) The role of the hydrophobic distal heme pocket of CooA in ligand sensing and response. J. Biol. Chem. 278:2333-2340.

9. Youn H, Kerby RL, Thorsteinsson MV, Clark RW, Burstyn JN and Roberts GP (2002) Analysis of the L116K variant of CooA, the heme-containing CO sensor, suggests the presence of an unusual heme ligand resulting in novel activity. J. Biol. Chem. 277:33616-33623.

8. Youn H, Kerby RL, Thorsteinsson MV, Conrad M, Staples CR, Serate J, Beack J and Roberts GP (2001) The heme pocket afforded by Gly117 is crucial for proper heme ligation and activity of CooA. J. Biol. Chem. 276:41603-41610.

7. Thorsteinsson MV, Kerby RL, Youn H, Conrad M, Serate J, Staples CR and Roberts GP (2001) Redox-mediated transcriptional activation in a CooA variant. J. Biol. Chem. 276:26807-26813.

6. Thorsteinsson MV, Kerby RL, Conrad M, Youn H, Staples CR, Lanzilotta WN, Poulos TL, Serate J and Roberts GP (2000) Characterization of variants altered at the N-terminal proline, a novel heme-axial ligand in CooA, the CO-sensing transcriptional activator. J. Biol. Chem. 275:39332-39338.

5. Youn H and Kang SO (2000) Enhanced sensitivity of Streptomyces seoulensis to menadione by superfluous lipoamide dehydrogenase. FEBS Lett. 472:57-61.

4. Cho SH, Na JU, Youn H, Hwang CS, Lee CH and Kang SO (1999) Sepiapterin reductase producing L-threo-dihydrobiopterin from Chlorobium tepidum. Biochem. J. 340:497-503.

3. Youn H, Kwak J, Youn HD, Hah YC and Kang SO (1998) Lipoamide dehydrogenase from Streptomyces seoulensis: biochemical and genetic properties. Biochim. Biophys. Acta 1388:405-418.

2. Cho SH, Na JU, Youn H, Hwang CS, Lee CH and Kang SO (1998) Tepidopterin, 1-O-(L-threo-biopterin-2'-yl)-beta-N-acetylglucosamine from Chlorobium tepidum. Biochim. Biophys. Acta 1379:53-60.

1. Youn HD, Youn H, Lee JW, Yim YI, Lee JK, Hah YC and Kang SO (1996) Unique isozymes of superoxide dismutase in Streptomyces griseus. Arch. Biochem. Biophys. 334:341-348.

Lab member

· Hwan Youn: PI

· Matt Hicks: graduate student (Biotechnology)

· Simranjeet Grover: graduate student (Biotechnology)

· Andres Nevarez: undergraduate student (Biology)

· Joseph Lin: graduate student (Biotechnology)

· Cameron Pospisil: graduate student (Biology)

· Joel Curiel: undergraduate student (Biology)

· Sanjiva Gunasekara: graduate student (Biology)

· Dhaval Waghela: graduate student (Biotechnology)

· Whitney Menefee: graduate student (Biology)

· Ashlee Girardin: graduate student (Biology)

· Jose Vera Jr.: undergraduate student (Biology)

· Sharasa Richards: undergraduate student (Biology)

· Former members

· Rebecca Freeman

· Jamie Russell

· Ana Arias

· Sanjeeta Shergill

· Venkata Kethanaboyina

· Kirk Karlozian

· Judy Ikawa

· Cindy Hua

· Anna Jo

· Mehak Goyal

· Danial Husain

· Rhythm Joshi

· Ming Lee Goh

· Samyuktha Dasari

· Zahra Al-Safwani

· Benjamin Kafer

· Ralph Delgado Jr.

Teaching

Fall 2011

· Functional Genomics (Biol 260T), Department of Biology, CSU-Fresno

Textbook: Microbial Functional Genomics and others

· Microbial Physiology (Biol 160), Department of Biology, CSU-Fresno

Textbook: The Physiology and Biochemistry of Prokaryotes

Spring 2011

· Nucleic Acid Technology Lab (Biol 243), Department of Biology, CSU-Fresno

Textbook: From Genes to Genomes

2010

· Molecular Biology 1 (Biol 241A), Department of Biology, CSU-Fresno

Textbook: Molecular Biology of the Gene

· Microbial Physiology (Biol 160), Department of Biology, CSU-Fresno

Textbook: The Physiology and Biochemistry of Prokaryotes

· General Microbiology Lab (Biol 120 Lab), Department of Biology, CSU-Fresno

· Microbiology Journal Club (Biol 189T), Department of Biology, CSU-Fresno

Flyer: MJC-2010

· Nucleic Acid Technology Lab (Biol 243), Department of Biology, CSU-Fresno

Textbook: From Genes to Genomes

2009

· Microbial Physiology (Biol 160), Department of Biology, CSU-Fresno

Textbook: The Physiology and Biochemistry of Prokaryotes

· Nucleic Acid Technology Lab (Biol 243), Department of Biology, CSU-Fresno

Textbook: The Condensed Protocols From Molecular Cloning: A Laboratory Manual

2008

· Microbial Physiology (Biol 160), Department of Biology, CSU-Fresno

Textbook: The Physiology and Biochemistry of Prokaryotes

· Seminar in Biological Science (Biol 281), Department of Biology, CSU-Fresno

2007-2008

· HHMI Teaching Fellow, University of Wisconsin-Madison

Editorial service

2009-present: Editor and reviewer, The Journal of Microbiology

Education

Ph.D., Microbiology, Seoul National University, South Korea, 1998

(Advisor: Dr. Sa-Ouk Kang)

M.S., Microbiology, Seoul National University, South Korea, 1993

(Advisor: Dr. Sa-Ouk Kang)

B.S., Microbiology, Seoul National University, South Korea, 1991

Professional experiences

2008- : Assistant Professor

Department of Biology, CSU-Fresno

2002-2008: Assistant Scientist

Department of Bacteriology, University of Wisconsin-Madison

(PI: Dr. Gary P. Roberts)

2000-2002: Postdoctoral Fellow

Department of Bacteriology, University of Wisconsin-Madison

(PI: Dr. Gary P. Roberts)

1998-2000: Postdoctoral Fellow

RCMM, Seoul National University, South Korea

(PI: Dr. Sa-Ouk Kang)