Freeze-sensitive labels and electronic time-temperature indicators are increasingly finding use in monitoring vaccines as they pass through the cold chain supply network. Paul Goddard, CEO of Protein Technologies, reveals how fluorescent proteins could provide a more reliable visual indication of freeze damage in future.
The presence of a fluorescent component in the bioluminescent organs of Aequorea victoria jellyfish was noted by Davenport and Nicol in 1955,1 but it was not until 1962 that Osamu Shimomura of Princeton University first realised that this fluorophore was in fact a protein.2
The complete primary sequence of the 238 amino acids of Aequorea green fluorescent protein (GFP) was not finally revealed until the cloning and sequencing of its cDNA by Prasher in 1992.3 Thereafter the biochemical community was quick to embrace its use in a wide variety of labelling and imaging applications both in vitro and in vivo.
It is now common research practice for biologists to introduce a gene (or a gene chimera) encoding an engineered fluorescent protein into living cells and subsequently to visualise the location and dynamics of the gene product using fluorescence microscopy.
Specialist fluorescent protein development company Protein Technologies Ltd (PTL), of Manchester, UK, has engineered a series of fluorescent proteins that can act as reliable visual indicators of the formation of the large ice-crystals that are responsible for freeze damage. It has long been known that these crystals are produced when freezing takes place slowly because of the reduced number of nucleation sites around which the nascent crystals can form, although it has hitherto not been possible to visualise this process by a small, low-cost external indicator.
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