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Monitoring folding transitions of synthetic, branched‐chain polypeptides by capillary zone electrophoresis
Author(s) -
Verzola Barbara,
Perduca Massimiliano,
Mezô Gábor,
Hudecz Ferenc,
Righetti Pier Giorgio
Publication year - 2003
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200390099
Subject(s) - radius of gyration , random coil , chemistry , circular dichroism , helix (gastropod) , folding (dsp implementation) , crystallography , hydrodynamic radius , protein folding , polymer , capillary electrophoresis , analytical chemistry (journal) , chromatography , organic chemistry , ecology , biochemistry , snail , electrical engineering , copolymer , biology , engineering
The coil/helix transition of a synthetic, branched‐chain polymeric polypeptide (poly (Lys(Glu 1 ‐ DL ‐Ala 3 )EAK), 50‐Lys residues long in the backbone, as a function of increasing molarities of methanol in solution, is here studied by both, circular dichroism (CD) and capillary zone electrophoresis. CD spectra showed that, at 75% v/v methanol, the transition from random coil to fully helical structure was obtained, in a pH 1.1 HCI solution in the presence of 20 m M NaCI. CZE studies, run in parallel, exhibited the classical unfolding to folding sigmoidal transition, with mid‐point at 60% v/v methanol concentration, plateauing at ca. 80% v/v organic solvent. Surprisingly, though, such unfolding to folding transition was accompanied by an expansion, rather than a contraction, of the resulting ordered polypeptide. As the charge of the polypeptide (a pure polycation at a pH of 2.1 in CZE) was kept rigorously constant, a plot of the radius of the polymer along the sigmoidal transition clearly showed that the radius of gyration of the helical, structured polypeptide was in fact larger than that of the random coil. Such results were confirmed by molecular dynamics simulations, which indicated that the dimensions of such polypeptide, in α‐helix configuration, were 8.5 nm (in length) and 3.2 nm (in diameter), whereas those of the corresponding random coil were 7.2 nm (in length) and 5.1 nm (length of shorter axis). It would thus appear that the randomized structure assumes the shape of a more compact object, roughly resembling a “rugby ball”.