The mammalian protein transcobalamin II (TCII) is responsible for the transport of vitamin B12 (more accurately termed cobalamin) through the bloodstream. Vitamin B12 is ingested and passed through gut ileal cells to the bloodstream where it is carried by transcobalamin II to cells presenting a specific TCII/cobalamin surface receptor. After receptor mediated endocytosis the vitamin requires further modification before adopting an active cofactor structure required for two enzymes, cytoplasmic methionine synthase (methyl-B12) and mitochondrial methylmalonyl CoA mutase (5'-deoxyadenosyl-B12). Genetic mutants of TCII cause an autosomal recessive disorder that presents itself in infancy with megaloblastic anemia. The 3-dimensional structure of transcobalamin II bound to cobalamin will be solved using X-ray crystallography, and will provide a molecular explanation of a human genetic disorder. The intestinal transport protein, intrinsic factor, shares high homology with TCII and will also be pursued structurally, either by homology modeling or direct structure determination.
Specific Aims : 1) Solve the three-dimensional structure of transcobalamin II by X-ray diffraction techniques, and investigate the structural basis for the physiological disruption of vitamin B12 transport. 2) Determine the critical interactions between TCII and cobalamin, and map the surface of the protein which interacts with the specific cell-surface receptor that recognises the TCII/cobalamin complex. 3) Produce a model of intrinsic factor (IF), haptocorrin and transcobalamin I (TCI) based on the high amino acid sequence identity with TCII.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Scientist Development Award - Research & Training (K01)
Project #
1K01DK002794-01
Application #
6031996
Study Section
Diabetes, Endocrinology and Metabolic Diseases B Subcommittee (DDK)
Program Officer
Hyde, James F
Project Start
2000-02-15
Project End
2002-11-30
Budget Start
2000-02-15
Budget End
2000-11-30
Support Year
1
Fiscal Year
2000
Total Cost
$75,949
Indirect Cost
Name
University of Utah
Department
Biochemistry
Type
Schools of Medicine
DUNS #
009095365
City
Salt Lake City
State
UT
Country
United States
Zip Code
84112
Schubert, Heidi L; Hill, Christopher P (2006) Structure of ATP-bound human ATP:cobalamin adenosyltransferase. Biochemistry 45:15188-96
Schubert, Heidi L; Blumenthal, Robert M; Cheng, Xiaodong (2003) Many paths to methyltransfer: a chronicle of convergence. Trends Biochem Sci 28:329-35
Schubert, Heidi L; Phillips, John D; Hill, Christopher P (2003) Structures along the catalytic pathway of PrmC/HemK, an N5-glutamine AdoMet-dependent methyltransferase. Biochemistry 42:5592-9
Mathews, M A; Schubert, H L; Whitby, F G et al. (2001) Crystal structure of human uroporphyrinogen III synthase. EMBO J 20:5832-9