THE ACTIVE-SITE STRUCTURE OF TETANUS NEUROTOXIN RESOLVED BY MULTIPLE-SCATTERING ANALYSIS IN X-RAY-ABSORPTION SPECTROSCOPY

A detailed study of the x-ray absorption spectrum of tetanus neurotoxi n in the K-edge EXAFS region of the zinc absorber is presented that al lows the complete identification of the amino acid residues coordinate d to the zinc active site. A Very satisfactory interpretation of the e xperimental data can be given if multiple scattering contributions are included in the analysis. Comparing the absorption spectrum of tetanu s neurotoxin to that of two other structurally similar zinc-endopeptid ases, thermolysin and astacin, in which the zinc coordination mode is known from crystallographic data, we conclude that in tetanus neurotox in, besides a water molecule, zinc is coordinated to two histidines an d a tyrosine.