Premium
pH‐dependent stability of the human α‐lactalbumin molten globule state: Contrasting roles of the 6—120 disulfide and the β‐subdomain at low and neutral pH
Author(s) -
Horng JiaCherng,
Demarest Stephen J.,
Raleigh Daniel P.
Publication year - 2003
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.10406
Subject(s) - molten globule , lactalbumin , chemistry , alpha lactalbumin , protein folding , native state , crystallography , folding (dsp implementation) , intermediate state , biophysics , circular dichroism , biochemistry , philosophy , theology , electrical engineering , biology , engineering
Many proteins are capable of populating partially folded states known as molten globule states. α‐Lactalbumin forms a molten globule under a range of conditions including low pH (the A‐state) and at neutral pH in the absence of Ca 2+ with modest amounts of denaturant. The A‐state is the most thoroughly characterized and thought to mimic a kinetic intermediate populated during refolding at neutral pH. We demonstrate that the properties and interactions that stabilize the A‐state and the pH 7 molten globule of human α‐lactalbumin differ. The unfolding of the wild‐type protein is compared to the unfolding of a variant that lacks the 6120 disulfide bond and to an autonomously folded peptide construct that we have previously shown represents the minimum core structure of the A‐state of human α‐lactalbumin. Studies conducted at pH 2 and 7 show that the disulfide makes little contribution to the stability of the molten globule at pH 7 but is important at pH 2. In contrast, the β‐subdomain of the protein is less important at pH 2 than at pH 7. The role of helix propensity in stabilizing the different forms of the molten globule state is examined and it is shown that it cannot account for the differences. The strikingly different behavior observed at pH 2 and 7 indicates that the A‐state may not be a rigorous mimic of the folding intermediate populated at pH 7. Proteins 2003;52:193–202. © 2003 Wiley‐Liss, Inc.