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Conformational stability of apoflavodoxin
Author(s) -
Genzor Carlos G.,
GómezMoreno Carlos,
Sancho Javier,
Beldarraín Alejandro,
LópezLacomba José Luis,
Cortijo Manuel
Publication year - 1996
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560050716
Subject(s) - chemistry , molten globule , circular dichroism , denaturation (fissile materials) , guanidine , crystallography , ionic strength , protein folding , native state , isoelectric point , urea , equilibrium unfolding , biochemistry , aqueous solution , nuclear chemistry , enzyme
Abstract Flavodoxins are α/β proteins that mediate electron transfer reactions. The conformational stability of apoflavodoxin from Anabœna PCC 7119 has been studied by calorimetry and urea denaturation as a function of pH and ionic strength. At pH > 12, the protein is unfolded. Between pH 11 and pH 6, the apoprotein is folded properly as judged from near‐ultraviolet (UV) circular dichroism (CD) and high‐field 1 H NMR spectra. In this pH interval, apoflavodoxin is a monomer and its unfolding by urea or temperature follows a simple two‐state mechanism. The specific heat capacity of unfolding for this native conformation is unusually low. Near its isoelectric point (3.9), the protein is highly insoluble. At lower pH values (pH 3.5‐2.0), apoflavodoxin adopts a conformation with the properties of a molten globule. Although apoflavodoxin at pH 2 unfolds cooperatively with urea in a reversible fashion and the fluorescence and far‐UV CD unfolding curves coincide, the transition midpoint depends on the concentration of protein, ruling out a simple two‐state process at acidic pH. Apoflavodoxin constitutes a promising system for the analysis of the stability and folding of α/β proteins and for the study of the interaction between apoflavoproteins and their corresponding redox cofactors.