ABSTRACT
The unusual behavior that certain proteins resist boiling temperatures, which cause “ordinary” globular proteins to precipitate, remained a curiosity unexplained for a long time. Such a behavior was described in the case of many intrinsically disordered proteins (IDPs) (see Figure 3.1), such as microtubule-associated protein 2 (MAP2) (Hernandez et al. 1986), calpastatin (Hackel, Konno, and Hinz 2000), α-synuclein (Weinreb et al. 1996), stathmin (Belmont and Mitchison 1996), epsin (Kalthoff et al. 2002), p21Cip1 (Kriwacki et al. 1996), protein phosphatase inhibitor 1 (Nimmo and Cohen 1978), 4E-BP1 (Fletcher and Wagner 1998) and 4E-BP3 (Poulin et al. 1998), involucrin (Etoh, Simon, and Green 1986), Df31 (Crevel and Cotterill 1995), inhibitor of PKA (PKIα) (Hauer et al. 1999a; Thomas et al. 1991), the homolog of PPI2 (Glc8) (Tung, Wang, and Chan 1995), group 2 LEA proteins ERD10 and ERD14 (Kovacs et al. 2008), fesselin (Khaymina et al. 2007), caldesmon (Bretscher 1984; Lynch, Riseman, and Bretscher 1987), calreticulin (Kim et al. 2000b), TPPP/p25 (Kovacs et al. 2004), and Pro-rich proteins of rat parotid glands (Muenzer et al. 1979). This behavior is very often exploited in the purification of proteins, to such an extent that it was actually suggested as a general method to purify recombinant IDPs (Kalthoff 2003). The reason for the heat
resistance of IDPs resides in their unusual amino acid composition; that is, they are highly charged and have a low content of hydrophobic amino acids (Dunker et al. 2001; Uversky, Gillespie, and Fink 2000a), due to which they do not expose hydrophobic residues that would make them aggregate at elevated temperatures.
