Ice-Binding Proteins - Not Only for Ice Growth Control

Abstract

Ice-binding proteins (IBPs) evolved in organisms living in cold ecosystems as a protective measure against freezing stresses. Some IBPs prevent their hosts from freezing mainly by depression of the freezing point of the body fluids below the melting point. Others help the organism avoid the damage of freezing by inhibiting ice recrystallization. These functions make IBPs excellent candidates for ice growth control, such as in cryopreservation of food and tissues. Organ banking, still in its infancy, is becoming a priority field for funding in order to revolutionize transplantation medicine and embryo preservation. To allow the use of IBPs in these applications, more basic knowledge about their function is needed. Recently we developed a new tool, called the mini cold finger, which allows us to grow a single ice crystal in a microfluidic channel and inspect the interactions of various IBPs with it. By injecting solutions of fluorescently-labeled IBPs into the device with an ice crystal present, we studied the ability of various IBPs to bind the basal plane of ice. Basal plane affinity is a crucial factor that directly affects the specific activity of IBPs. We further showed that the dynamics of binding of IBPs to the basal plane differs from one type of IBP to another. In another work we studied the IBP from an Antarctic marine bacterium, Marinomonas primoryensis. We showed that this IBP has a different function than any other known IBP, which is as an adhesin that helps the bacterium stick to ice crystals. Antibodies raised against the ice-binding part of the protein abolished the ability of the bacteria to bind ice, while antibodies raised against other parts of the protein failed to do so. This principle of “knocking out” the adhesion function can theoretically be used to prevent formation of biofilms, thereby combating infections. This is currently the only example known of an adhesin that binds to ice. Funding: ERC, ISF, CHIR, NSERC.