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Chemical protein synthesis and racemic protein crystallization were used to determine the X-ray structure of the snow flea antifreeze protein (sfAFP). Crystal formation from a racemic solution containing equal amounts of the chemically synthesized proteins d-sfAFP and l-sfAFP occurred much more readily than for l-sfAFP alone. More facile crystal formation also occurred from a quasi-racemic mixture of d-sfAFP and l-Se-sfAFP, a chemical protein analogue that contains an additional -SeCH2- moiety at one residue and thus differs slightly from the true enantiomer. Multiple wavelength anomalous dispersion (MAD) phasing from quasi-racemate crystals was then used to determine the X-ray structure of the sfAFP protein molecule. The resulting model was used to solve by molecular replacement the X-ray structure of l-sfAFP to a resolution of 0.98 A. The l-sfAFP molecule is made up of six antiparallel left-handed PPII helixes, stacked in two sets of three, to form a compact brick-like structure with one hydrophilic face and one hydrophobic face. This is a novel experimental protein structure and closely resembles a structural model proposed for sfAFP. These results illustrate the utility of total chemical synthesis combined with racemic crystallization and X-ray crystallography for determining the unknown structure of a protein.

X-ray structure of snow flea antifreeze protein determined by racemic crystallization of synthetic protein enantiomers., Pentelute BL, Gates ZP, Tereshko V, Dashnau JL, Vanderkooi JM, Kossiakoff AA, Kent SB, J Am Chem Soc. 2008 Jul 30;130(30):9695-701. Epub 2008 Jul 4. PMID:18598029

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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Categories: Protein complex | Dashnau, J. | Gates, Z P. | Kossiakoff, A A. | Kurutz, J. | Pentelute, B L. | S B.H., Kent. | Tereshko, V. | Vaderkooi, J M. | Antifreeze protein | Mirror image protein | Quasi-racemate | Racemic protein crystallography | Sfafp