Growth?melt asymmetry in ice crystals under the influence of spruce budworm antifreeze protein

PERTAYA N.; CELIK Y.; DI PRINZIO, CARLOS LEONARDO

JOURNAL OF PHYSICS CONDENSED MATTER

IOP PUBLISHING LTD

Año: 2007 vol. 19 p. 1 - 12

0953-8984

Here we describe studies of the crystallization behavior of ice in an aqueoussolution of spruce budworm antifreeze protein (sbwAFP) at atmosphericpressure. SbwAFP is an ice binding protein with high thermal hysteresisactivity, which helps protect Choristoneura fumiferana (spruce budworm)larvae from freezing as they overwinter in the spruce and fir forests of the northeastern United States and Canada. Different types of ice binding proteins havebeen found in many other species. They have a wide range of applications incryomedicine and cryopreservation, as well as the potential to protect plants andvegetables from frost damage through genetic engineering. However, there ismuch to learn regarding the mechanism of action of ice binding proteins. In ourexperiments, a solution containing sbwAFP was rapidly frozen and then meltedback, thereby allowing us to produce small single crystals. These maintainedtheir hexagonal shapes during cooling within the thermal hysteresis gap.Melt/growth/melt sequences in low concentrations of sbwAFP reveal the sameshape transitions as are found in pure ice crystals at low temperature (−22 ◦C)and high pressure (2000 bar) (1); while both growth and melt shapes displayfacetted hexagonal morphology, they are rotated 30◦ relative to one another.Moreover, the initial melt shape and orientation is recovered in the sequence.To visualize the binding of sbwAFP to ice, we labeled the antifreeze proteinwith enhanced green fluorescent protein (eGFP) and observed the sbwAFP-GFPmolecules directly on ice crystals using confocal microscopy. When coolingthe ice crystals, facets form on the six primary prism planes (slowest growingplanes) that are evenly decorated with sbwAFP-GFP. During melting, apparentfacets form on secondary prism planes (fastest melting planes), leaving residualsbwAFP at the six corners of the hexagon. Thus, the same general growthmelt behavior of an apparently rotated crystal that is observed in pure ice underhigh pressure and low temperature is reproduced in ice under the influence ofsbwAFP at ambient pressure and temperatures near 0 ◦C.