th  - 1987 - 51st ENC Conference

MF21
SOLID-STATE 13C AND 15N NMR STUDIES OF CROSSLINKING IN
BACTERIAL CELL WALLS
Joel R. Garbow*
Life Sciences NMR Center
Monsanto Company
St. Louis, 140 63198.
Jacob Schaefer
Department of Chemistry
Washington University
St. Louis, 140 63130.
The cell walls of many Gram-positive bacteria are composed of glycan
backbones with attached short peptide stems. Crosslinks can form
between amino acids on adjacent peptide stems, contributing to the
structural integrity of the cell wall; We are using cross-polarization
magic-angle spinning 13C and 15N NMR to measure the extent and mobility
of peptidoglycan crosslinks in the cell wall of the bacterium Aerococcus
viridans. In lyophillzed samples, we use double cross-polarization
NMR,a technique which detects quantitatively 13C-15N chemical bonds,
to observe directly the crosslink. Motions of the protein backbone
and of the crosslink site in both lyophilized and wet-cell samples
are measured through measurements of NH dipolar and 15N chemical-shift
tensors.
The partial collapse of dipolar and chemical-shift tensors for peptide
NH and for the amide NH at cell-wall crossllnk sites, of intact lyophi-
lized A. vlrldans cells, indicate NH-vector root-mean-square angular
fluctuations of 23 °. This result is consistent with the local mobility
calculated in typical psec-regime computer simulations of protein
dynamics in the solid state. The experimental root-mean-square angular
fluctuations for both types of NH vectors increase to 37 ° for viable
wet cells at I0 ° C. The similarity in mobilities for both general
protein and cell-wall peptidoglycan suggests that the additional motion
in wet cells does not involve independent local motions of individual
cell components.