Methods in Biosynthesis and Characterization of the Antifreeze Protein (AFP) for Potential Blood Cryopreservation

The cryopreservation of red blood cells (RBCs) is very important to modern medicine. Cryoprotectants (CPAs) such as dimethyl sulfoxide (DMSO), proline, trehalose, and polyvinyl alcohol (PVA) have been used in the cryopreservation of RBCs, but the results are not satisfactory. Marinomonas primoryensis antifreeze protein (MpAFP) is a Ca2+-dependent AFP derived from Antarctic bacteria, which can prevent bacteria from freezing under extremely cold conditions and may be suitable for cryopreservation of RBCs. The active region of MpAFP is located in region IV and is called MPAFP_RIV. In this paper, the gene of region IV of MpAFP is introduced into BL21 (DE3) competent cells, and MpAFP_RIV is obtained after culture, separation, and purification. The improved splat assay is proposed, and this method first proves that MpAFP_RIV has strong ice recrystallization inhibition (IRI) activity without Ca2+. The improved splat assay is easier to operate and lower the cost compared to the traditional one, and the results are consistent with the classic sucrose sandwich assay, proving that this method can accurately detect IRI activity. The feasibility of MPAFP_RIV combined with classical CPA for cryopreservation of RBCs and the methods to increase the yield of MPAFP_RIV are proposed.

Protection of Alcohol Dehydrogenase against Freeze–Thaw Stress by Ice-Binding Proteins Is Proportional to Their Ice Recrystallization Inhibition Property

Ice-binding proteins (IBPs) have ice recrystallization inhibition (IRI) activity. IRI property has been extensively utilized for the cryopreservation of different types of cells and tissues. Recent reports demonstrated that IRI can also play a significant role in protecting proteins from freezing damage during freeze–thaw cycles. In this study, we hypothesized that the protective capability of IBPs on proteins against freeze–thaw damage is proportional to their IRI activity. Hence we used two IBPs: one with higher IRI activity (LeIBP) and the other with lower activity (FfIBP). Yeast alcohol dehydrogenase (ADH) was used as a freeze-labile model protein. IBPs and ADH were mixed, frozen at −20 °C, and thawed repeatedly. The structure of ADH was assessed using fluorescence emission spectra probed by 1-anilinonaphthalene-8-sulfonate over the repeated freeze–thaw cycles. The activity was monitored at 340 nm spectrophotometrically. Fluorescence data and activity clearly indicated that ADH without IBP was freeze-labile. However, ADH maintained about 70% residual activity after five repeated cycles at a minimal concentration of 0.1 mg mL-1 of high IRI-active LeIBP, but only 50% activity at 4 mg mL−1 of low active FfIBP. These results showed that the protection of proteins from freeze–thaw stress by IBPs is proportional to their IRI activity.