Antifreeze proteins (AFPs) are a unique class of cryoprotectants that function not by penetrating cells or purely by osmotic means, but by directly interacting with ice crystals to control their formation and growth. This ice-binding property makes them powerful, non-toxic alternatives or additives to conventional cryoprotectants like DMSO.
Mechanism of Cryoprotection
AFPs, also known as ice-binding proteins (IBPs), protect biological material through two principal, interrelated activities:
- Thermal Hysteresis (TH): This is the ability of AFPs to lower the freezing point of a solution non-colligatively, while leaving the melting point largely unaffected, creating a gap between the two. This is achieved through the adsorption of AFPs to the surface of ice crystals via a specific ice-binding face (IBF), which inhibits further ice growth.
- Ice Recrystallization Inhibition (IRI): This is considered the more critical function for cryopreservation. During warming, small ice crystals can merge into larger, more damaging ones—a process called recrystallization. AFPs adsorb onto the ice crystal surfaces and prevent this growth, thereby minimizing mechanical damage to cells and tissues.
