Open AccessThe Conformation of Small Proteins
Author(s) -
Chicheportiche Robert,
Lazdunski Michel
Publication year - 1970
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1970.tb00322.x
Subject(s) - urea , optical rotatory dispersion , chemistry , denaturation (fissile materials) , crystallography , stereochemistry , circular dichroism , nuclear chemistry , organic chemistry
The conformation of neurotoxin II of Androctonus Australis Hector has been studied by optical rotatory dispersion and ultraviolet difference spectrophotometry. Depending upon pH and temperature, the protein exists under, at least, four different molecular forms, I, II, III and D which are in rapid equilibrium. A state‐diagram has been obtained which describes the different zones of temperature and pH in which forms I, II, III and D are stable. A physico‐chemical analysis of all transconformations has been carried out. The acidic as well as the alkaline transition (I ⇌ II, and I ⇌ III respectively) are controlled by the unmasking of structurally important ionisable groups, one of them being probably the carboxylic side‐chain of an aspartic or a glutamic acid. Form I, which is predominant between pH 4 and 9 and below 30°, contains a high degree of ordered structure. It is very stable toward heat denaturation and remains folded in 9.5 M urea, while form II, its conformational isomer at acidic pH, is completely unfolded at 50° or in high concentrations of urea. A very low cooperativeness has been observed for the unfolding of form II in urea or at high temperatures.