It's Easy Being Green

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Science  26 May 2006:
Vol. 312, Issue 5777, pp. 1107
DOI: 10.1126/science.312.5777.1107d

Porous solids are widely used in chromatographic separations based on size and shape. Some pores are as large as proteins (for instance, in dextran- or agarose-based gel filtration), whereas others are as small as water molecules (as in molecular sieves used to keep organic solvents dry). Paukstelis has assessed the permeation properties of a self-assembled three-dimensional lattice constructed from four assembly strands [each 24 nucleotides (nt) long] and an 11-nt spacer strand. The estimated diameter of the largest internal solvent channel in crystals of this DNA array was 9 nm, which corresponds to a globular protein of 300 kD, but the measured size cutoff for negatively charged proteins appeared to be only one-10th this size (ovalbumin, no; carbonic anhydrase, yes), perhaps as a result of electrostatic interactions. Confocal microscopy revealed that the interior of a crystal soaked in a mixture of green fluorescent protein and a much bigger red maltose-binding protein was green and not red. — GJC

J. Am. Chem. Soc. 128, 10.1021/ja061322r (2006).

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