417
J. Am. Chem. Soc. 1994,116, 417-418
Interactions of the D and L-Forms of Winter Flounder Antifreeze Peptide with the (201) Planes of Ice
Table 1. Binding Energies of Winter Flounder Antifreeze Peptide on the (201) Plane of Ice I*
isomer
Jeffry D. Madura,'.? Andrzej Wierzbicki: John P. Harrington) Richard H. Maughon,? James A. Raymond? and C. Steven Sikest
Department of Chemistry and Department of Biologkal Sciences, University of South Alabama Mobile. Alabama 36688
direction
[in]
L L D D
[I%] [ilz]
encrgy/(kcal/mol)o N+ N-282 -234 -242 -288
-199 -195 -195 -203
liizi a N+ represents the N-terminus pointing in the direclion of the bipyramidal apex, while N- represents the opposite direction.
Received August 16. 1993 Antifreeze peptides and glycopeptidesfound in cold water fishes have been studied experimentally for two decades1" and computationally for thelast eight years."lO In their pioneeringwork, Knight et al. used etch marks on single ice crystals to identify the planeson which, and the probahledirections along which, several antifreezesbindtoice.llJ2 They proposed that thewinter flounder antifreeze peptide (WF), a right-handed a-helix, binds to the (201)" bipyramidal planes of ice Is along the [I121 direction, a direction whose repeat distance, 16.7 A, nearly matches that of the WF polar groups. Recently, Wen and Laursen synthesized an all-D-isomerof WF that had the same antifreeze activity as its natural L-enantiomer." They suggested that the o-isomer, being a mirror image of the L-isomer, should bind in a mirror symmetry-related direction along the [Ti21 vector. In this communication, using molecular modeling and energy minimization calculations, we demonstrate that indeed the D-isomer preferentially binds along the mirror-related [iIZ]direction and analyze the nature of the binding preference for the L- and *isomers We employed molecular modeling and energy minimization methods to studv the binding of W F to the (201) . . biDvramidal ._ planesof iceIhalong the twomirror symmetry-equivalentvectors [I121 and [TI2]. The ice surfaces were constructed from the asymmetric fractional coordinates of ice" using CERIUS 3.2.l6 Once the surface was constructed, the hydrogen positions of ice wererandomizedby runninga 5-ps, 2OOOKdynamicscalculation, in which the oxygen positions were held fixed, followed by 500
-
Department of Chemistry.
1Deparlment of
Biological Scimcss.
(I) D c V " ~ , A. L. Phil. Tram. R . Soe. London B. B i d . Sei. 1984, 304,
