W0109

Enhancing Protein Crystallization Through Precipitant Synergy. Shahzad Majeed, Gilad Ofek, Adam Belachew, Peter D. Kwong, NIH/NIAID/VRC, 40 Convent Dr., MSC 3027, Rm 4609, Bethesda, MD 20892 USA.

Suitable conditions for protein crystallization are commonly identified through sparse matrix screening of combinations of independent factors that affect crystal formation. Precipitating agents are prime determinants of crystallization, and function by at least three different mechanisms: by altering the activity coefficient of water (salts), by altering the dielectric constant of the solvating medium (organic solvents), or by increasing molecular crowding (high molecular weight polymers like polyethylene glycol). However, in crystallization they are rarely treated combinatorially, as independent factors. We devised a crystallization screen, which we call the Precipitant Synergy (PS) screen, which had at least two mechanistically independent precipitants in each condition. Tests with HIV-1 envelope-related proteins showed that the use of the PS screen increased the probability of growing diffraction quality crystals. Tests with hen egg-white lysozyme, a commonly crystallized protein, generated a C2 crystal, which had not been previously described. The results indicate that mechanistically distinct precipitants can synergize, with precipitant combinations adding novel dimensions to protein crystallization.