ELECTRON-DENSITY MAPS OF LYSOZYME CALCULATED USING SYNCHROTRON LAUE DATA COMPRISING SINGLES AND DECONVOLUTED MULTIPLES

Abstract

We have used lysozyme as a test case to illustrate the application of a new method of estimating the intensities of Laue multiples reflection data in protein crystallography. Hen egg-white lysozyme, an enzyme with a single polypeptide chain 129 amino acids, crystallizes in space group P4(3)2(1)2 with cell parameters a = b 79.1 angstrom, c = 37.9 angstrom. Laue image plate data were collected using synchrotron radiation on station 9.5 at Daresbury with a total exposure time of 0.95 seconds. The data processed were separated into two data sets comprising the singles and the combined singles and deconvoluted multiples. The method of deconvolution was that of Campbell and Hao (1993), which utilizes the intensity variation of the lambda-curve. Electron density maps (2F(o) - F(c)) based on the two data sets are then compared. This comparison shows that the deconvoluted multiples do indeed contribute usefully to the continuity of the maps due to the improved completeness of the data. A number of map sections along the polypeptide chain, based on the two Laue data sets, are shown for comparison. These include Arg 5, His 15, Phe 38, Asp 52, Tyr 53, Pro 70, Trp 108 and the four disulphide bridges.