A fragment of staphylococcal nuclease with an OB-fold structure shows hydrogen-exchange protection factors in the range reported for 'molten globules'

Abstract

Hydrogen exchange rates for an OB-fold subdomain fragment of staphylococcal nuclease have been measured at pH 4.7 and 4°C, conditions close to the minimum of acid/base catalyzed exchange. The strongest protection from solvent exchange is observed for residues from a five- stranded β-barrel in the NMR structure of the protein. Protection factors, calculated from the experimental hydrogen-exchange rates, range between 1 and 190. Similarly small protection factors have in many cases been attributed to 'molten globule' conformations that are supposed to lack a specific tertiary structure. The present results suggest that marginal protection from solvent exchange does not exclude well-defined structure.