Kannan and Vishveshwara ( 2000) suggested that aromatic clusters are important in thermostabilisation.ĭisulfide bridges bind two cysteine residues in the peptide chain with a covalent bond. Cation-π bonds that form between the positively charged residues arginine and lysine and the aromatic residues, particularly Tyr and Trp, have been suggested to be of importance in thermostabilisation by Chakravarty and Varadarajan ( 2002) as well as Gromiha et al. Das and Gerstein ( 2000) found that thermophilic proteins contain considerably more charged residues, and likely also more salt bridges, than mesophiles. Of the earliest factors mentioned is salt bridges, and a number of groups have studied their stabilising effects (Zhou and Dong 2003 Thomas and Elcock 2004 Elcock 1998). Many studies of thermostabilisation have been done on the structure level. Proteins from psychrophiles are likewise thought to be more difficult to purify and crystalise, which likely is the reason why there are relatively few structures of cold adapted proteins, while there are more sequences of these than for thermophiles in the genomic databases.
Because they are easier to purify, and probably also to crystallise, they have been picked out among homologues when a representative protein for a family was to be picked, especially in structural genomics studies (Jenney and Adams 2008). First, they are stable at temperatures where most proteins get denature, and have therefore been attractive to use in order to understand what makes proteins stable in general. Thermophilic proteins have been the most studied ones for several reasons. This is generally interpreted to mean that there must be more subtle differences in interactions and packing that make up most of the differences between them (Kumar et al. Despite this, the basic building blocks of DNA and proteins are the same, and a pair of homologous proteins from one psychrophilic and one thermophilic species may have almost identical structure. Life can be found in arctic and antarctic waters holding temperatures below the ordinary freezing point of water, to superheated water in hot springs and in deep ocean smokers, where some organisms can survive temperatures up to 121☌ (Kashefi and Lovley 2003). One of the most remarkable adaptations is the range of temperatures life has adapted to. Life has a great ability to adapt to the most diverse habitats, and almost all places on earth have a variety of life forms.
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