A preliminary neutron crystallographic study of proteinase K at pD 6.5

Abstract

A preliminary neutron crystallographic study of the proteolytic enzyme proteinase K is presented. Large hydrogenated crystals were prepared in deuterated crystallization buffer using the vapor-diffusion method. Data were collected to a resolution of 2.3 A on the LADI-III diffractometer at the Institut Laue-Langevin (ILL) in 2.5 d. The results demonstrate the feasibility of a full neutron crystallographic analysis of this structure with the aim of providing relevant information on the location of H atoms, particularly at the active site. This information will contribute to further understanding of the molecular mechanisms underlying the catalytic activity of proteinase K and to an enriched understanding of the subtilisin clan of serine proteases.

Figure 1

Hydrogenated proteinase K crystals grown in deuterated buffer at pD 6.5 by vapor diffusion. The estimated crystal volume is 0.81 mm³. Visualization was by transmitted polarized white light.

Figure 2

An enlarged view of one quarter of a quasi-Laue neutron diffraction image from proteinase K collected in 8 h on the LADI-III beamline at the Institut Laue–Langevin. The horizontal axis of the figure spans approximately half of the full detector width.

Figure 3

The stereographic projection of averaged radial completeness demonstrates complete angular coverage of the unique octant (and thus full sampling of the asymmetric unit in reciprocal space), which resulted in an overall data completeness of 70.8%.