Richard Sabina, Ph.D.
Associate Professor
Dr. Sabina received his Bachelor of Science degree in Biology at the Pennsylvania State University in 1974. He received his Master of Science degree in 1976 and his Doctorate degree in 1979 in Genetics from Texas A&M University. From 1979 to 1981, Dr. Sabina was a postdoctoral fellow at Duke University Medical Center, where he initiated his studies of purine metabolism in humans with an emphasis on AMP deaminase. From 1982 to 1987 he was a research associate in the Howard Hughes Medical Institute at Duke University Medical Center, where he was appointed as a Research Assistant Professor in the Department of Medicine, a position he held from 1983 to 1989. Dr. Sabina joined the faculty of the Medical College in 1989.
Contact Information
sabinar@mcw.edu
Phone: (414) 456-4697
Fax: (414) 456-6510
Research Interests
AMP deaminase (AMPD) is a highly regulated enzyme that catalyzes a branchpoint reaction in the ATP catabolic pathway and competes with AMP-preferring cytosolic 5'-nucleotidase (cNT-I) for available substrate (Figure 1). This competition can be illustrated in different striated muscles during periods of energy imbalance, where catabolic flow proceeds primarily through AMPD in exercising skeletal muscle and through cNT-I in ischemic cardiac muscle. There are three AMPD genes in humans that exhibit tissue-specific and developmental patterns of expression and each polypeptide has a conserved C-terminal catalytic domain and a divergent N-terminal regulatory domain. Altered AMPD gene expression and enzyme regulation in different situations have provided clues about the functional significance of this enzyme.
Figure 1. Adenylate metabolism in human tissues and cells. Net catabolism of ATP during periods of energy imbalance disrupts adenylate kinase equilibrium and leads to increased production of AMP. Competition between AMPD and cNT-I for available substrate forms the basis for regulation of these branchpoint reactions. Hypoxanthine is the major salvageable substrate in all tissues and cells, but the developmental loss of adenylosuccinate synthetase in erythrocytes blocks the resynthesis of AMP from both salvage and de novo sources of IMP.
Current Research Projects:
AMP deaminase in a disturbed erythrocyte calcium homeostasis;
AMPD assumes an even greater role in the energy metabolism of erythrocytes, where the developmental loss of adenylosuccinate synthetase prevents the synthesis of AMP from both de novo and salvage synthesis precursors of IMP (Figure 1). Consequently, AMP deamination in erythrocytes results in an irreversible depletion of the adenine nucleotide pool. Normally, erythrocyte AMPD is maintained in a relative inactive state, but increased enzyme activity is observed during oxidative stress and in Familial Phosphofructokinase Deficiency (Tarui's disease), which hastens the loss of adenine nucleotides and promotes increased hemolysis. We have recently discovered that Ca2+-calmodulin binds and activates erythrocyte AMPD (isoform E). Currently, we are examining isoform E regulation in two clinical conditions of a disturbed calcium homeostasis, Familial Phosphofructokinase Deficiency and Sickle Cell Disease.
AMP Deaminase is Required for Plant Life;
Plants contain only one AMPD gene and a new project in the lab is focused on the corresponding enzyme, which is essential for the early stages of embryonic development and is also an identified herbicide target. However, the underlying biochemical basis for the critical role(s) that AMPD plays in plant development and growth has not been addressed, nor has the enzyme been well characterized in any species. We have recently discovered that plant AMPD has an N-terminal transmembrane domain and have also solved the crystal structure of an Arabidopsis N-truncated recombinant enzyme in collaboration with the Center for Eukaryotic Structural Genomics (CESG) at the University of Wisconsin-Madison. Currently, we are using a variety of biochemical, molecular and cellular approaches to explore the functional significance of plant AMPD in order to build on the information generated from this structure.
Selected Publications
"Disturbed Erythrocyte Calcium Homeostasis and Adenine Nucleotide Dysregulation in Canine Phosphofructokinase Deficiency." Sabina, R.L., Woodliff, J.E., and Giger, U., Comparative Clinical Pathology (ahead-of-print), 2007
"Adenine nucleotide pool perturbation is a metabolic trigger for AMP deaminase inhibitor-based herbicide toxicity" Sabina RL, Paul AL, Ferl RJ, Laber B, and Lindell SD Plant Physiol 143: 1752-1760 (2007)
"Membrane association, mechanism of action, and structure of Arabidopsis EMBRYONIC FACTOR 1" Han BW, Bingman CA, Mahnke DK, Bannen RM, Bednarek SY, Sabina RL, Phillps GN Jr. J Biol. Chem. 281: 14939-14947 (2006)
"The contribution of Ca2+-calmodulin activation of human erythrocyte AMP deaminase (isoform E) to the erythrocyte metabolic dysregulation of familial phosphofructokinase deficiency." Sabina RL, Waldenstrom A, Ronquist G. Haematologica 91: 652-655 (2006)
"Calcium activates erythrocyte AMP deaminase (isoform E) through a protein-protein interaction between calmodulin and the N-terminal domain of the AMPD3 polypeptide." D.K. Mahnke, and R.L. Sabina Biochemistry 44: 5551-5559 (2005)
"N-terminal extensions of the human AMPD2 polypeptide influence ATP regulation of isoform L." A.L. Haas and R.L. Sabina Biochem. Biophys. Res. Comm. 305: 421-427 (2003)
"Expression, purification, and inhibition of in vitro proteolysis of human AMPD2 (isoform L) recombinant enzymes."A.L. Haas, and R.L. Sabina Protein Express. Purif. 27: 293-303 (2003)
"N-terminal sequence and distal histidine residues are responsible for pH-regulated cytoplasmic membrane binding of human AMP deaminase isoform E." D.K. Mahnke-Zizelman, and R.L. Sabina J. Biol. Chem. 277: 42654-42662 (2002)
"Localization of N-terminal sequences in human AMP deaminase isoforms that influence contractile protein binding." D.K. Mahnke-Zizelman and R.L. Sabina Biochem. Biophys. Res. Comm. 285: 489-495 (2001)
"Towards an understanding of the functional significance of N-terminal domain divergence in human AMP deaminase isoforms." R.L. Sabina and D.K. Mahnke-Zizelman Pharmacol. Therapeut. 87: 279-283 (2000)
"Regulation of AMP deaminase by phosphoinositides." B. Sims, D.K. Mahnke-Zizelman, A.A. Profit, G.D. Prestwich, R.L. Sabina, and A.B. Theibert J. Biol. Chem. 274: 25701-25707 (1999)
"Novel aspects of tetramer assembly and N-terminal domain structure and function are revealed by recombinant expression of human AMP deaminase isoforms." D.K. Mahnke-Zizelman, P.C. Tullson, and R.L. Sabina J. Biol. Chem. 273: 35118-35125 (1998)
"Elevated adenosine monophosphate deaminase activity in Alzheimer's disease brain." B. Sims, R.E. Powers, R.L. Sabina, and A.B. Theibert Neurobiol. Aging 19: 385-391 (1998)