查看文章

A recombinant form of the NH2-terminal propeptide of human pulmonary surfactant protein B precursor (SP-BN) has been produced in Escherichia coli. The conformational stability of the protein to pH acidification was studied by far-UV circular dichroism (CD). The secondary structure of the propeptide changed moderately from pH 7 to 4.1 and was much recovered after regaining neutrality. The emission of the fluorescent probe bis-ANS at pH 4.2 but not at neutral pH indicates that the propeptide adopts a molten globule-like state at pH 4. The effect of alkaline pH on the protein followed by CD and fluorescence spectroscopies indicates that the ionization of an amino acid residue with an apparent pK= 8.05±0.15 was responsible of the observed conformational changes in the propeptide.