title: Ice nucleation of an insect lipoprotein ice nucleator (LPIN) correlates with retardation of the hydrogen bond dynamics at the myo-inositol ring.
abstract: Remarkably little is known about the mechanism of action of ice nucleation proteins (INPs), although their ability to trigger ice nucleation could be used in a broad variety of applications. We present CD measurements of an insect lipoprotein ice nucleator (LPIN) which show that the lipoproteins consist of a high amount of β-structures (35%). Terahertz absorption spectroscopy is used to probe the influence of the LPIN on the H-bond network dynamics. We observe a small, but significant THz excess, as an indication of an influence on the H-bond network dynamics. When adding the ice nucleation inhibitor sodium borate, this effect is considerably reduced, similar to that observed before for antifreeze glycoproteins (AFGPs). We propose that myo-inositol, the functional group of phosphatidylinositols, is crucial for the observed change of the H-bond network dynamics of hydration water. This hypothesis is confirmed by additional THz experiments which revealed that the influence of myo-inositol on the hydrogen bond network can be blocked by sodium borate, similar to the case of LPINs. Interestingly, we find a less significant effect when myo-inositol is replaced for chiro- and allo-inositol which underlines the importance of the exact positioning of the OH groups for the interaction with the H-bond network. We propose that a local ordering of water molecules is supporting ice nucleation activity for the LPIN in a similar way to that found for AFP activity in the case of hyperactive insect AFPs.
authors.affiliation: Lehrstuhl für Physikalische Chemie II, Ruhr-Universität, 44801 Bochum, Germany. martina.havenith@rub.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Bäumer
authors.forename: John G
authors.initials: JG
authors.lastname: Duman
authors.forename: Martina
authors.initials: M
authors.lastname: Havenith
mesh_terms: D000818:Animals; D021301:Antifreeze Proteins / Q000737:chemistry*; D001425:Bacterial Outer Membrane Proteins; D006859:Hydrogen; D006860:Hydrogen Bonding; D007294:Inositol / Q000737:chemistry*; D007313:Insecta / Q000737:chemistry*; D008074:Lipoproteins / Q000737:chemistry* / Q000378:metabolism; D014867:Water
chemical_list: D021301:Antifreeze Proteins; D001425:Bacterial Outer Membrane Proteins; D008074:Lipoproteins; C063113:ice nucleation protein; D014867:Water; D007294:Inositol; D006859:Hydrogen