Alternative polymer precipitants for protein crystallization

A set of 16 inexpensive and commercially available polymer precipitants were tested for protein crystallization. Eight of them were found suitable: polyethylene glycol dimethyl ether of molecular weight (MW) 500, 1000 and 2000; di[poly(ethylene glycol)] adipate, MW 900; poly(ethylene glycol-ran-propylene glycol), MW 2500 and 12000; poly(acrylic acid) sodium salt, MW 2100; and polyethylene glycol methyl ether methacrylate, MW 1100. Two new crystallization screens, PolyA and PolyB, were formulated using these eight polymers, each containing 96 solutions - four polymers in combination with 24 common salts and buffers, covering pH values from 4.5 to 9.0. The screens were tested on 29 proteins, 21 of which were crystallized. The tests confirmed the applicability of the eight polymers as precipitants for protein crystallization.