Norma M. Allewell

We study the biochemical mechanisms of action of multisubunit proteins, particularly those involved in nitrogen metabolism. Binding of ligands to these proteins typically causes changes in folding and subunit interactions that mediate and regulate their biological activity. We study these structural changes and their relationship to function by X-ray crystallography, computer modeling and a variety of physical biochemical and enzymological approaches.

Much of our work has focused on E. coli aspartate transcarbamylase, an enzyme that catalyzes the first committed step in pyrimidine biosynthesis, and which has a complex allosteric regulatory mechanism. More recently, we have begun studying enzymes of the urea cycle that are involved in human disease in collaboration with Dr. Mendel Tuchman of the Children's National Medical Center. Initially we studied ornithine transcarbamylase, which is
homologous to the catalytic subunit of aspartate transcarbamylase. This enzyme is important clinically, because mutations in it cause OTCD, a
relatively common disease, particularly in newborns, in which levels of ammonia in the blood are elevated, leading to neurological damage. New
areas of emphasis include the ornithine transporter protein which is found in the mitochondrial membrane, a collaboration with Dr. Marco Colombini
(Department of Biology, University of Maryland) and N-acetylglutamate synthase (NAGS). N-acetylglutamate synthase, the product of the
reactioncatalyzed by NAGS, is an essential allosteric activator of carbamoylphosphate synthase I, the first enzyme of the urea cycle. Patients who cannot produce
N-acetylglutamate develop hyperammonia. We have cloned the human enzyme and begun its biochemical characterization.

Caldovic, L., Morizono, H., Panglao, M. G., Gallegos, R., Yu, Ziaolin, Shi,
D., Malamy, M. H., Allewell, N. M., and Tuchman, M. Cloning and expression
of the human N-acetylglutamate synthase gene. Biochem. Biophys. Res. Comm., 299, 581-586 (2002).

Caldovic, L., Morizono, H., Yu, X., Thompson, M., Shi, D., Gallegos, R.,
Allewell, N. M., Malamy, M. H. and Tuchman, M. Identification, cloning
and expression of the mouse N-acetylglutamate synthase gene. Biochem. J.,
364, 825-31 (2002)

Shi, D., Gallegos, R., Deponte, J., 3rd, Morizono, H., Yu, X., Alewell, N.
M. , Malamy, M. and Tuchman, M. Crystal structure of a
transcarbamylase-like protein from the anaerobic bacterium bacteroides
fragilis at 2.0 A resolution. J. Mol. Biol. 320, 899-908 (2002)

Shi, D., Morizono, H., Yu, X., Tong, L., Allewell, N. M. and Tuchman, M.
Human ornithine transcarbamylase: crystallographic insights into substrate recognition and
conformational changes. Biochem. J. 354, 501-9
(2001)

Shi D, Morizono H, Aoyagi M, Tuchman M, Allewell N M. Crystal structure of
human ornithine transcarbamylase complexed with carbamoyl phosphate and L-norvaline at 1.9 A
resolution. Proteins 39(4):271-7 (2000).

Allewell N M, Shi D, Morizono H,Tuchman M. Molecular Recognition by
Ornithine and Aspartate Transcarbamylases. Acc. Chem. Research.
32(10) 885-894 (1999).