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J. Biol. Chem., Vol. 279, Issue 29, 30433-30439, July 16, 2004

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Solution Structure of Spheniscin, a -Defensin from the Penguin Stomach^*

Céline Landon, Cécile Thouzeau¶, Henri Labbé, Philippe Bulet||, and Françoise Vovelle**

From the Centre de Biophysique Moléculaire, CNRS UPR 4301, Université d'Orléans, rue Charles Sadron, 45071 Orléans Cedex 2, France, the Centre d'Ecologie et de Physiologie Energétiques, CNRS UPR 9010, 23 rue Becquerel, 67087 Strasbourg Cedex 02, France, and ^||Atheris Laboratories, Case Postale 314, CH-1233 Bernex, Geneva, Switzerland

Recently two -defensins, named spheniscins, have been isolated from the stomach content of the king penguin (Aptenodytes patagonicus), which is capable of preserving food for several weeks during egg incubation (Thouzeau, C., Le Maho, Y., Froget, G., Sabatier, L., Le Bohec, C., Hoffmann, J. A., and Bulet, P. (2003) J. Biol. Chem. 278, 51053–51058). It has been proposed that, in combination with other antimicrobial peptides, spheniscins may be involved in this long term preservation of food in the bird's stomach. To draw some structure/function features, the three-dimensional structure in aqueous solution of the most abundant spheniscin (Sphe-2) was determined by two-dimensional NMR and molecular modeling techniques. The overall fold of Sphe-2 includes a three-stranded antiparallel -sheet stabilized by three disulfide bridges with a pairing typical of -defensins. In addition, the N-terminal segment shows helical features on most structures. Sphe-2 is highly cationic, and its surface displays a hydrophobic patch. Comparative modeling revealed that this patch is preserved in avian defensins. The activity of Sphe-2 against a pathogenic Gram-positive strain was retained in vitro in the conditions of osmolarity found in penguin stomach content and also in different salt concentrations and compositions up to those reported for seawater. Comparison with structurally related mammalian -defensins showed that the hydrophobic patch is not preserved in mammalian -defensins and that the high cationicity of Sphe-2 is presumably the critical factor for its retained activity in high salt concentrations. Such peculiarities, in addition to a broad activity spectrum, suggest that penguin defensins may represent interesting probes for the design of highly efficient antibiotics to fight off pathogens that develop in relatively salt-rich body fluids.

Received for publication, February 6, 2004 , and in revised form, April 26, 2004.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains the following supporting information: 1) proton chemical shifts of Sphe-2 (2 mM H₂O/D₂O, pH 4.3, 293 K), 2) TOCSY spectrum (80 ms, H₂O/D₂O, pH 4.3, 293 K), 3) NOESY spectrum (160 ms, H₂O/D₂O, pH 4.3, 293 K), and 4) short TOCSY spectra recorded in D₂O to monitor the exchange data and compared with the reference TOCSY in H₂O.

The amino acid sequence of spheniscin-2 reported in this paper has been submitted to the Swiss Protein Database under Swiss-Prot accession no. P83430.

The atomic coordinates and structure factors (code 1UT3) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^¶ Supported by a grant from the Ars Cuttoli-Paul Appell fund of the Fondation de France.

Deceased August 5, 2003.

^** To whom correspondence should be addressed. Tel.: 33-2-38-25-55-74; Fax: 33-2-38-63-15-17; E-mail: vovelle{at}cnrs-orleans.fr.

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