Heat inactivation of proteins: implications for the Mars Sample Campaign and other extraterrestrial sample return missions

Abstract Spaceflight missions must limit biological contamination on both the outbound and return legs to comply with planetary protection requirements. Depending on the mission profile, contamination concerns may include the potential presence of bioactive molecules as defined by NASA’s Planetary Protection policies. Thus, the present study has examined the temperature and time requirements for sufficient inactivation/degradation of an infectious, heat-stable prion protein (Sup35NM), which serves as a model bioactive molecule. Bovine serum albumin was used to establish the method parameters and feasibility. Differential scanning calorimetry, Fourier transform infrared spectroscopy, analytical reversed-phase high-performance liquid chromatography, and mass spectrometry were utilized to analyze heat-treated samples, with non-treated samples serving as controls. Heat treatment at 400°C for 5 seconds was found to result in substantial decomposition of Sup35NM. In addition to the disruption of the protein backbone amide bonds, the side chain residues were also compromised. Fragments of molecular weight <4600 were observed by mass spectrometry but the impact of treatment on both the backbone and side chains of Sup35NM suggested that these fragments would not self-associate to create potentially pathogenic entities. The present methodology provided insight into the protein degradation process and can be applied to a variety of treatment strategies (e.g., any form of sterilization or inactivation) to ensure a lack of protein-based contamination of isolated extraterrestrial specimens.