Multinuclear NMR Probes of Biological Systems

Armitage, Ian

Abstract

The objectives of this group revolve around the use of sophisticated multinuclear NMR techniques to elucidate the solution strucutre, molecular dynamics and mechanism of action of a variety of biological systems. During the past year we have extended our NMR investigations of the mechanistic and structural role of the multiple metal ions in the E. coli enzyme alkaline phosphatase. These studies have included 3lp NMR of the enzyme phosphate intermediates, 113Cd NMR on the 113Cd2 ion substituted enzyme and 13C and 15N NMR on the enzyme labeled biosynthetically with (gamma-13C)-and/or (15 N pi)-histidine. 113Cd NMR has been used to determine the structure of the multiple metal-binding sites in the two major isoproteins of metallothionein (MT) from rabbit liver and kidney, and from crab hepatopancreas. Rabbit MT's were found to contain two separate metal clusters, one containing 4 113Cd ions and the other containing 3. Crab MT's contain two 3-metal clusters. Detailed structural and kinetic data pertaining to the metal ions in this protein is essential to understanding the biological function of this protein. Chemical and 13C NMR techniques have also been used to determine the composition and structural aspects of the blood group M and N active sialoglycopeptides from human glycophorin A. These studies have related that the M and N-active sialoglyco-octapeptides both have identical oligosaccharide structures. These data are consistent with a model in which the M or N determinant is the aminoterminal amino acid and a NeuNAc residue(s). Lastly, preliminary studies are underway to evaluate the potential of techniques such as cryoenzymology and solid state NMR in biological systems where conventional NMR methods are limited due to chemical exchange modulation.