Urea equilibrium unfolding of the major core protein of the retrovirus feline immunodeficiency virus and its tryptophan mutants

Circular dichroism and fluorescence spectroscopy have been employed to stud y the urea unfolding mechanism of a recombinant form of the major core prot ein of feline immunodeficiency virus (FIV-rp24) and its native tryptophan m utants. The equilibrium denaturation curves indicate the existence of two t ransitions. The first unfolding transition most likely reflects the denatur ation of the carboxy-terminal region of FIV-rp24. Consequently, the second transition, where the changes in fluorescence are produced, should reflect the denaturation of the amino-terminal region. If the intermediate observed upon urea denaturation is an on-pathway species, the data described herein can reflect the sequential and independent loss of structure of the two do mains that this type of proteins possesses. (C) 2001 Elsevier Science B.V. All rights reserved.