HIGH RESOLUTION (1.05Å) STRUCTURE OF SALMONELLA TYPHIMURIUM NEURAMINIDASE (SIALIDASE) Garman, E.1, Wouters, J.2, Vimr, E.3, Laver, G.4, Sheldrick, G.M.2, 1Laboratory of Molecular Biophysics, University of Oxford, Oxford. U.K. 2Department of Chemistry, University of Gottingen, Gottingen, Germany. 3University of Illinois, Urbana, U.S.A. 4A.N.U., Canberra, Australia.
Atomic resolution data have been obtained from a crystal of salmonella typhimurium neuraminidase (STNA) held at 100K, and the structure has been refined using SHELXL (1). Currently the crystallographic R and free R values are 10.2% and 13.2% respectively for the model of this 42kD enzyme.
The crystal structure of STNA has previously been published at 2.0Å resolution (2) and determined at 1.6Å resolution (3). The enzyme consists of six four-stranded antiparallel beta-sheets arranged as the blades of a propeller around an axis passing through the active site.
The greatly improved resolution reported here was achieved by lowtemperature (100K) data collection conducted at BW7B beamline of the DESY Hamburg synchrotron radiation source. X-ray diffraction data were 92% complete in all shells to 1.0Å with a merging R(I) value of 6.2%. The crystals are of space group P212121 and cell 47.4Å, 82.3Å and 91.7Å.
The 1.6Å model has been refined against all data to 1.05Å using SHELXL. This model currently includes 381 amino acids, 6 glycerol molecules (from the cryoprotectant agent), and 670 waters. Anisotropic B factors were fitted to all atoms. The electron density maps calculated using the refined model are extremely clean and the protein structure is very well defined apart from 3 N-terminal residues. Atomicity is achieved in most regions of the protein.
An atomic resolution molecular model of a large enzyme has thus been obtained using the tools now available to the protein crystallographer.
(1) Sheldrick, G.M. and Schneider, T.R. (1996) Methods Enzymol., Eds. Carter, C.W. and Sweet, R.M., in press.
(2) Crennell, S.J. Garman, E.F., Laver, W.G., Vimr, E.R. and Taylor, G.L. (1993) Proc. Natl. Acad. Sci. USA 90, 9852-9856.
(3) Crennell, S.J. Garman, E.F., Laver, W.G., Vimr, E.R. and Taylor, G.L. (Submitted to J.M.B.)