Equilibrium Unfolding of Partially Folded Staphylococcal Nuclease A₂- and A₃-forms is Accompanied by the Formation of an Intermediate State

V. N. Uversky^1,2

¹Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (095) 924-0493; E-mail: uversky@vega.protres.ru

²Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia

Received August 25, 1997

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Structural properties of an equilibrium intermediate formed upon urea-induced unfolding of more ordered staphylococcal nuclease A-forms (A₂ and A₃) are studied. The effect of association on the structural properties and conformational stability of this unfolding intermediate is also considered. A close structural similarity (including tendency for association) is shown between this intermediate and the least ordered A₁-form, induced in the acid-unfolded nuclease by moderate sulfate or chloride concentrations.

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KEY WORDS: staphylococcal nuclease, partially-folded states, anion-induced forms, association, equilibrium unfolding intermediate

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