Environmental adjustments of the cooperativity in M13 phage thermal denaturation

Abstract

The filamentous bacteriophage M13 has been widely used in phage display and as a scaffold for nanostructures. Although M13 is loosely described as a thermo-resistant virus, no thorough studies of its thermostability have been reported so far. By using differential scanning calorimetry (DSC), we characterized the thermal stability of M13 in aqueous buffer and in the presence of ethanol. M13 was found to be very thermostable indeed, being resistant to the combined effects of temperature and high ethanol content. Upon thermal denaturation, several subunits of the major coat protein apparently undergo a cooperative conformational change, leading to the formation of residual β-strand conformation. Furthermore, the cooperativity of the denaturation process changes drastically with pH and ethanol concentration, indicating that P8 moieties are able to adjust its intermolecular packing in response to the environment. Deconvolution of DSC scans allowed the estimation of the number of P8 molecules comprising one cooperative unit.