14th International Conference on the Physics and Chemistry of Ice (PCI-2018 in Zürich)

Freezing by protein cages

11 Jan 2018, 15:20

20m

NO Building, Room C 60 (ETH Zürich, centre)

Talk Ice Binding Proteins

Speaker

Prof. Alexander Bittner (CIC nanogune)

Description

Assembled proteins, esp. cages and viruses, are essential ingredients of life [Calo 2016a]. Some assemblies appear to tolerate the contact to ice, or even the growth of ice. While the interaction of single proteins or simple biopolymers with ice is increasingly investigated [Hiranuma 2015], assemblies are new territory [Wilson 2015]. We pose two questions: 1. Molecular geometry: Is there evidence for the proposal of flat and large surfaces as efficient ice binders or nucleators? This idea [Davies 2014] is intriguing because it puts a purely physical mechanism above the usually assumed biochemical processes, although arguments such as hydrophobicity are also linked to the surface chemistry. 2. Cloud glaciation by biological ice nuclei: Can viruses induce freezing of water? This question is a natural extension from standard ice nucleating particles (mineral dust), over organic matter to "living" objects, which are indeed present in large numbers in sea water [Wilson 2015]. Since the surfaces even of small viruses are less curved and larger than the surface of a single protein, both questions are related. We are answering them by testing the freezing of supercooled water by selected proteins and protein assemblies. Our methods are microscopy, AFM [Calo 2016b], (nano)FTIR [Amenabar 2013] and environmental SEM [Alonso 2013a]; our proteins were the cages ferritin and apoferritin (each with 24 proteins), casein (aggregating to hundreds of nm), and a standard plant virus, Tobacco Mosaic Virus (TMV), which features a helical sheath of 2130 proteins [Alonso 2013b, Calo 2016b]. This virus is hydrophilic, and can be transported in clouds [Castello 1995]. We found a preference for ice growth induced by aggregated (assembled) proteins. Apoferritin and ferritin are especially effective. These assemblies are virus-like cages, constructed from 24 proteins, with a natural tendency to form aggregates (e.g. oligomers). Based on our studies on virus hydration [Alonso2013a], we now demonstrate that ice can grow on viruses without destruction. High-resolution AFM shows surface reconstructions of irregular lateral spacings (ca. 10 nm) that are caused by water adsorption, which is the precursor for ice formation. Literature: [Alonso 2013a] J.M. Alonso, F. Tatti, A. Chuvilin, K. Mam, T. Ondarçuhu, A.M. Bittner, Langmuir 29 (2013) 14580-14587 [Alonso 2013b] J.M. Alonso, M.L. Gorzny, A.M. Bittner, Trends Biotechnol. 31 (2013) 530-538 [Amenabar 2013] I. Amenabar, S. Poly, W. Nuansing, E.H. Hubrich, A. Govyadinov, F. Huth, R. Krutokhvostov, L. Zhang, M. Knez, J. Heberle, A.M. Bittner, R. Hillenbrand, Nature Commun. 4 (2013) 2890 [Calo 2016a] A. Calò, S. Eiben, M. Okuda, A.M. Bittner, Jap. J. Appl. Phys. 55 (2016) 03DA01 [Calo 2016b] A. Calò, A. Eleta-Lopez, P. Stoliar, D. de Sancho, S. Santos, A. Verdaguer, A.M. Bittner, Sci. Rep. 6 (2016) 21899 [Castello 1995] J.D. Castello et al., Phytopathology 85 (1995) 409 [Davies 2014] P.L. Davies, Trends in Biochem. Sci. 39 (2014) 548 [Hiranuma 2015] N. Hiranuma et al., Nature Geoscience 8 (2015) 273 [Wilson 2015] T.W. Wilson et al., Nature 525 (2015) 234

Significance statement

Protein assemblies, such as protein cages and viruses, can induce ice growth. We provide a nanoscale view on this phenomenon. We propose that surface hydration is the first stage of ice nucleation.