W0261

Solution Structure of Detergent Micelles at Conditions Relevant to Membrane Protein Crystallization. V. Urban, K. Littrell and P. Thiyagarajan, IPNS Division, Argonne National Laboratory, Argonne, IL 60439, USA

An understanding of membrane protein crystallization is of central importance in structural biology. Integral membrane proteins require detergent solutions in order to be solubilized in aqueous media. The presence of detergent greatly complicates the phase map for protein crystallization. This arises due to the fact that both detergent and protein solubilities are altered by the chemical additives that are used for crystallization. Electrically neutral detergents are preferably used in protein crystallization, as they prevent alteration of the charge properties of solubilized proteins. The non-ionic decanoyl-N-methyl glucamide (DMG) and zwitterionic 1,2-diacyl-sn-glycero-3-phosphocholine (SPC) have been used in the crystallization of cytochrome bc(1) complex¹. Using small angle neutron scattering we examined the formation of DMG and SPC micelles as a function of the respective detergent concentration and ionic strength. Furthermore, we also studied the effects of additives (glycerol and polyethylene glycol) alone as well as in combination typical for actual membrane protein crystallization. These studies reveal that the DMG micelles are rod-like with a cross sectional radius of 12 Å. The size of DMG micelles increases with increasing ionic strength, but decreases with the addition of glycerol. The CMC of DMG decreased at higher ionic strength. SPC micelles are spherical in shape. But their behavior with respect to ionic strength and additives is similar to that of DMG. Details of the micelle formation in these detergent solutions will be discussed.

1. Xia, D., Yu, C.A., Kim, H., Xia, J., Kachurin, A.M., Zhang, L., Yu, L. and Deisenhofer, J., Science 277, 60 (1997)

This work was supported by the U.S. Department of Energy, BES-Materials Science, under contract W-31-109-ENG-38.