Dr. Mark O'Brian Biochemistry 140 Farber Hall Buffalo NY, 14214 Phone: (716) 829-3200 Email: mrobrian@buffalo.edu View map

DESCRIPTION OF INTERESTS

Metabolic Regulation in Bacteria and Plants Rhizobia are developmentally regulated bacteria that differentiate to establish a symbiosis with leguminous plants within root nodules of the plant. Likewise, the nodule is a plant organ that arises from an altered development of root cells triggered by interactions with the bacterium. The symbiosis is very energy intensive, and heme protein synthesis is induced by both partners during nodule ontogeny to accommodate this demand. My lab focuses on aspects of heme biosynthesis in the Bradyrhizobium japonicum-soybean symbiosis as a means of understanding mechanistic and regulatory processes associated with development and cellular function. Heme synthesis in B. japonicum is an intriguing regulatory problem because data indicate that it can be formed from a plant-derived precursor, hence segments of a pathway are spatially separated between two organisms. In addition, heme formation by the prokaryote is under developmental control and is coordinated with the cellular oxygen and iron status. From the plant perspective, we found that heme synthesis genes are strongly induced in response to interactions with its bacterial partner, thus each symbiont exerts an effect on the other with respect to heme formation. It is becoming increasing clear that the seemingly esoteric processes involved in establishing and maintaining symbiosis are variations on themes common to bacteria, plants and eukaryotes in general. Moreover, numerous phenomena identified with symbiosis, which include aspects of heme formation and function, have become paradigms for providing the conceptual framework for general biological problems.

EDUCATION

1984	Doctor of Philosophy, Biology Johns Hopkins University
1980	Bachelor of Science, State University of New York at Albany

EXPERTISE

Genetic Control of Heme Biosynthesis Heme is involved in many cellular processes as the active moiety of proteins involved in respiration, oxidative stress response, redox reactions and signal transduction. Heme is also a regulatory molecule that controls gene expression at the level of transcription, translation, protein targeting and protein stability. My lab is interested in the genetic control of heme biosynthesis, and in understanding the role of heme as regulatory molecule. The bacterium Bradyrhizobium japonicum is a good model for studying the control of heme synthesis because it can readily adapt to changes in its environment and to external stresses. Our current work addresses the following questions: 1) What physiological and environmental factors control heme biosynthesis? 2) How are heme biosynthesis genes regulated at the molecular level? 3) How can heme serve as a signaling molecule to mediate the regulation of gene expression? We identified the Iron Response Regulator (Irr), a protein that belongs to the Fur family of transcriptional regulators that mediates iron-dependent regulation of the heme biosynthesis. Irr is also regulated by iron at the level of protein degradation, a process mediated by heme. Irr interacts directly with ferrochelatase, the enzyme which catalyzes the final step of the heme pathway. We are addressing the hypothesis that control of heme biosynthesis involves a novel regulatory function of a biosynthetic enzyme to affect gene expression. Finally, we are defining the role of Irr in cellular oxidative stress response.

PUBLICATIONS

Finan, T.M. O'Brian, M.R. Layzell, D.B. Vessey, J.K. Newton, W.; Nitrogen Fixaton: Global Perspectives; 2002 May;

O'Brian, M.R. Thoeny-Meyer, L.; Biochemistry, regulation and genomics of heme biosynthesis in prokaryotes; Advances in Microbial Physiology; 2002 May; 46; 257-318

Qi, Z. O'Brian, M.R.; Interaction between the bacterial iron response regulator and ferrochelatase mediates genetic control of heme biosynthesis; Molecular Cell; 2002 Jan; 9; 155-162

King ND, O'Brian MR; Evidence for direct interaction between enzyme I(Ntr) and aspartokinase to regulate bacterial oligopeptide transport.; J Biol Chem; 2001 Jul; 276(24); 21311-21316

King ND, Hojnacki D, O'Brian MR; The Bradyrhizobium japonicum proline biosynthesis gene proC is essential for symbiosis.; Appl Environ Microbiol; 2000 Dec; 66(12); 5469-5471

O'Brian, M.R.; Heme biosynthesis and function in he Rhizobium-legume symbiosis; Prokaryotic Nitrogen Fixation: A Model System for the Analysis of a Biological Process; 2000 May;

Hamza I, Qi Z, King ND, O'Brian MR; Fur-independent regulation of iron metabolism by Irr in Bradyrhizobium japonicum.; Microbiology; 2000 Mar; 146 (; 669-676

Qi Z, Hamza I, O'Brian MR; Heme is an effector molecule for iron-dependent degradation of the bacterial iron response regulator (Irr) protein.; Proc Natl Acad Sci U S A; 1999 Nov; 96(23); 13056-13061

Hamza I, Hassett R, O'Brian MR; Identification of a functional fur gene in Bradyrhizobium japonicum.; J Bacteriol; 1999 Sep; 181(18); 5843-5846

Sangwan I, O'Brian MR; Expression of a soybean gene encoding the tetrapyrrole-synthesis enzyme glutamyl-tRNA reductase in symbiotic root nodules.; Plant Physiol; 1999 Feb; 119(2); 593-598

O'Brian, M.R.; Regulation of bacterial heme biosynthesis by iron; Iron Metabolism: Inorganic Biochemistry and Regulatory Mechanisms; 1999 Jan;

Hamza I, Chauhan S, Hassett R, O'Brian MR; The bacterial irr protein is required for coordination of heme biosynthesis with iron availability.; J Biol Chem; 1998 Aug; 273(34); 21669-21674

Chauhan S, Titus DE, O'Brian MR; Metals control activity and expression of the heme biosynthesis enzyme delta-aminolevulinic acid dehydratase in Bradyrhizobium japonicum.; J Bacteriol; 1997 Sep; 179(17); 5516-5520

Chauhan S, O'Brian MR; Transcriptional regulation of delta-aminolevulinic acid dehydratase synthesis by oxygen in Bradyrhizobium japonicum and evidence for developmental control of the hemB gene.; J Bacteriol; 1997 Jun; 179(11); 3706-3710

King ND, O'Brian MR; Identification of the lrp gene in Bradyrhizobium japonicum and its role in regulation of delta-aminolevulinic acid uptake.; J Bacteriol; 1997 Mar; 179(5); 1828-1831

Chauhan, S. O'Brian, M.R.; Regulation of Bradyrhizobium japonicum hemB, a heme biosynthesis gene.; Biological Fixation of Nitrogen for Ecology and Sustainable Agriculture; 1997 Mar;

O'Brian MR; Heme synthesis in the rhizobium-legume symbiosis: a palette for bacterial and eukaryotic pigments.; J Bacteriol; 1996 May; 178(9); 2471-2478

Chauhan S, O'Brian MR; A mutant Bradyrhizobium japonicum delta-aminolevulinic acid dehydratase with an altered metal requirement functions in situ for tetrapyrrole synthesis in soybean root nodules.; J Biol Chem; 1995 Aug; 270(34); 19823-19827

McGinnis, S.D. O'Brian, M.R.; The rhizobial hemA gene is required for symbiosis in species with deficient delta-aminolevulinic acid uptake activity; Plant Physiology; 1995 Aug; 108; 1547-1552

Frustaci JM, Sangwan I, O'Brian MR; gsa1 is a universal tetrapyrrole synthesis gene in soybean and is regulated by a GAGA element.; J Biol Chem; 1995 Mar; 270(13); 7387-7393

Kaczor CM, Smith MW, Sangwan I, O'Brian MR; Plant delta-aminolevulinic acid dehydratase. Expression in soybean root nodules and evidence for a bacterial lineage of the Alad gene.; Plant Physiol; 1994 Apr; 104(4); 1411-1417

Chauhan S, O'Brian MR; Bradyrhizobium japonicum delta-aminolevulinic acid dehydratase is essential for symbiosis with soybean and contains a novel metal-binding domain.; J Bacteriol; 1993 Nov; 175(22); 7222-7227

Frustaci JM, O'Brian MR; Analysis of the Bradyrhizobium japonicum hemH gene and its expression in Escherichia coli.; Appl Environ Microbiol; 1993 Aug; 59(8); 2347-2351

Sangwan I, O'Brian MR; Expression of the soybean (Glycine max) glutamate 1-semialdehyde aminotransferase gene in symbiotic root nodules.; Plant Physiol; 1993 Jul; 102(3); 829-834

Frustaci JM, O'Brian MR; The Escherichia coli visA gene encodes ferrochelatase, the final enzyme of the heme biosynthetic pathway.; J Bacteriol; 1993 Apr; 175(7); 2154-2156

Frustaci JM, O'Brian MR; Characterization of a Bradyrhizobium japonicum ferrochelatase mutant and isolation of the hemH gene.; J Bacteriol; 1992 Jul; 174(13); 4223-4229

Sangwan, I. O'Brian, M.R.; Characterization of delta-aminolevulinic acid formation in soybean root nodules; Plant Physiology; 1992 Mar; 98; 1074-1079

Frustaci JM, Sangwan I, O'Brian MR; Aerobic growth and respiration of a delta-aminolevulinic acid synthase (hemA) mutant of Bradyrhizobium japonicum.; J Bacteriol; 1991 Feb; 173(3); 1145-1150

Sangwan, I. O'Brian, M.R.; Evidence for an inter-organismic heme biosynthetic pathway in symbiotic soybean root nodules; Science; 1991 Feb; 251; 1220-1222

O'Brian MR, Maier RJ; Molecular aspects of the energetics of nitrogen fixation in Rhizobium-legume symbioses.; Biochim Biophys Acta; 1989 May; 974(3); 229-246

O'Brian, M.R. Maier, R.J.; Hydrogen Metabolism in Rhizobium: Energetics, regulation, enzymology and genetics.; Advances in Microbial Physiology; 1988 Apr; 29; 1-52

O'Brian MR, Kirshbom PM, Maier RJ; Bacterial heme synthesis is required for expression of the leghemoglobin holoprotein but not the apoprotein in soybean root nodules.; Proc Natl Acad Sci U S A; 1987 Dec; 84(23); 8390-8393

O'Brian, M.R. Maier, R.J.; Isolation of a cytochrome aa3 gene from Bradyrhizobium japonicum; Proc. Natl. Acad. Sci. USA; 1987 Jun; 84; 3219-3223

O'Brian MR, Kirshbom PM, Maier RJ; Tn5-induced cytochrome mutants of Bradyrhizobium japonicum: effects of the mutations on cells grown symbiotically and in culture.; J Bacteriol; 1987 Mar; 169(3); 1089-1094

O'Brian MR, Maier RJ; Expression of cytochrome o in hydrogen uptake constitutive mutants of Rhizobium japonicum.; J Bacteriol; 1985 Feb; 161(2); 507-514

O'Brian MR, Maier RJ; Role of ubiquinone in hydrogen-dependent electron transport in Rhizobium japonicum.; J Bacteriol; 1985 Feb; 161(2); 775-777

O'Brian MR, Maier RJ; Involvement of cytochromes and a flavoprotein in hydrogen oxidation in Rhizobium japonicum bacteroids.; J Bacteriol; 1983 Aug; 155(2); 481-487

Mutaftschiev, S. O'Brian, M.R. Maier, R.J.; Hydrogen oxidation activity in membranes from Rhizobium japonicum.; Biochim. Biophys. Acta; 1983 Jul; 722; 372-380

O'Brian MR, Maier RJ; Electron transport components involved in hydrogen oxidation in free-living Rhizobium japonicum.; J Bacteriol; 1982 Oct; 152(1); 422-430