Alber

Birgit Alber
Assistant Professor

B.S. Univ. of Marburg
Ph.D. Virginia Tech
Postdoc. Univ. of Freiburg

Campus Address: 
417A BioSci
Office Phone: 
614-247-4443
Lab Phone: 
614-247-2517
Email: 
alber.8
ALBER LAB
PUBLICATIONS

RESEARCH INTERESTS

Biochemistry of carbon metabolism

Purple non-sulfur bacteria are some of the metabolically most versatile organisms known. Rhodobacter sphaeroides, Rhodospirillum rubrum, Rhodopseudomonas palustris, etc.are capable to use a variety of modes for energy conservation: they either utilize light as an energy source (under anoxic conditions) or organic and inorganic compounds as electron donors and acceptors (respiratory and fermentative growth). This remarkable metabolic versatility of non-sulfur purple bacteria extends to the utilization of a large spectrum of carbon sources: ranging from carbon dioxide (autotrophic growth) to fermentative products generated by other organisms in the same habitats. R. sphaeroides has been studied extensively in several aspects of metabolism, the organism is genetically accessible, and the sequence of its genome is available. This then provides an excellent opportunity to uncover novel metabolic routes involving unique carbon transformations using R. sphaeroides as a model organism.

The ethylmalonyl-CoA pathway for acetyl-CoA assimilation

Growth on organic substrates that are metabolized via acetyl-CoA (such as fatty acids, alcohols, and esters, including various fermentation products, but also waxes, alkenes, taurine, and methylated compounds) requires the synthesis of all cell constituents from this C2-unit. Fifty years ago Kornberg and Krebs established the glyoxylate cycle as an anaplerotic reaction sequence for the citric acid cycle, allowing cell carbon biosynthesis from acetyl-CoA (May 18, 1957; Nature 17: 988 – 991). Recently we described the ethylmalonyl-CoA pathway for assimilation of acetyl-CoA in the absence of a functional glyoxylate cycle (Alber et al., 2006, Erb et al., 2007).

The key enzyme of the ethylmalonyl-CoA pathway is a novel carboxylase catalyzing the reductive carboxylation of an enoyl-CoA substrate: crotonyl-CoA carboxylase/reductase. The enzyme, for which the catalytic mechanism is under investigation, connects the C4- and C5-branch of the pathway. The following C5-transformations are also unique. We use biochemical and genetic approaches to elucidate and study the individual enzymatic reactions involved.

Reactions of the ethylmalonyl-CoA pathway also provide the extender units for the biosynthesis of several antibiotics by polyketide synthases in actinomycetes. For methylotrophic bacteria such as Methylobacterium extorquens extension of the serine cycle with reactions of the ethylmalonyl-CoA pathway leads to a simplified scheme for isocitrate lyase-independent C1 assimilation.

RELEVANT PUBLICATIONS

  • Laguna R, Tabita FR, & Alber BE.(2011) Acetate-dependent photoheterotrophic growth and the differential requirement for the Calvin-Benson-Bassham reductive pentose phosphate cycle in Rhodobacter sphaeroides and Rhodopseudomonas palustris. Arch Microbiol. 193,151-154.
  • Alber BE (2011) Biotechnological potential of the ethylmalonyl-CoA pathway. Appl Microbiol Biotechnol.  89,17-25.
  • Erb TJ, Frerichs-Revermann L, Fuchs G & Alber BE. (2010) The apparent malate synthase activity of Rhodobacter sphaeroides due to two paralogous enzymes, (3S)-malyl-coenzyme A (CoA)/beta-methylmalyl-CoA lyase and (3S)-malyl-CoA thioesterase. J Bacteriol. 192, 1249-58.
  • Erb TJ, Fuchs G, & Alber BE. (2009) (2S)-Methylsuccinyl-CoA dehydrogenase closes the ethylmalonyl-CoA pathway for acetyl-CoA assimilation. Mol Microbiol. 73, 992-1008 (Comment in the same issue).
  • Erb TJ, Brecht V, Fuchs G, Müller M& Alber BE. (2009) Carboxylation mechanism and stereochemistry of crotonyl-CoA carboxylase/reductase, a carboxylating enoyl-thioester reductase. Proc Natl Acad Sci U S A. 106, 8871-6.
  • Erb TJ, Rétey J, Fuchs, G & Alber BE. (2008) Ethylmalonyl-CoA mutase from Rhodobacter sphaeroides defines a new subclass of coenzyme B12-dependent acyl-CoA mutases. J Biol Chem. 283,32283-93. 
  • Alber BE, Kung JW & Fuchs G. (2008) 3-Hydroxypropionyl-coenzyme A synthase from Metallosphaera sedula, an enzyme involved in autotrophic CO2 fixation. J. Bacteriol. 190,1383-9.
  • Zarzycki J, Schlichting A, Strychalsky N, Müller M, Alber BE & Fuchs G. (2008) Mesaconyl-coenzyme A hydratase, a new enzyme of two central carbon metabolic pathways in bacteria. J Bacteriol. 190,1366-74.
  • Erb TJ, Berg IA, Brecht V, Müller M, Fuchs G & Alber BE. (2007) Synthesis of C5-dicarboxylic acids from C2-units involving crotonyl-CoA carboxylase/reductase: the ethylmalonyl-CoA pathway. Proc Natl Acad Sci U S A. 104,10631-6.
  • Alber BE, Spanheimer R, Ebenau-Jehle C & Fuchs G. (2006) Study of an alternate glyoxylate cycle for acetate assimilation by Rhodobacter sphaeroides. Mol Microbiol. 61, 297-309.
  • Meister M, Saum S, Alber BE & Fuchs G. (2005) L-Malyl-coenzyme A / b-methylmalyl-coenzyme A lyase is involved in acetate assimilation of the isocitrate lyase-negative bacterium Rhodobacter capsulatus. J Bacteriol. 187,1415-25.
  • Alber BE & Fuchs G. (2002) Propionyl-coenzyme A synthase from Chloroflexus aurantiacus, a key enzyme of the 3-hydroxypropionate cycle for autotrophic CO2 fixation. J Biol Chem. 277,12137-43.

The all-time favorites:

  • Alber, B. E. and Ferry, J. G. (1994) A carbonic anhydrase from the archaeon Methanosarcina thermophila. Proc Natl Acad Sci.U S A. 91, 6909-13.
  • Alber BE & Fuchs G. (2002) Propionyl-coenzyme A synthase from Chloroflexus aurantiacus, a key enzyme of the 3-hydroxypropionate cycle for autotrophic CO2 fixation. J Biol Chem. 277,12137-43.