Detection of Molten Globule State in β-lactoglobulin by a Novel Palladium (II) Complex

The refolding studies of the typical globular proteins, including β- lactalbumin, lysozyme, cytochrome c and apo-myoglobin, have shown the presence of a transient structural intermediate at an early stage of the folding reaction. Since their properties were common to many proteins, the general term molten globule (MG) was coined [1-2].The structural characteristics of the transient intermediate as well as the MG state are delineated as follows. Firstly, the MG state,which is structurally distinct from both the native (N) and denatured (D) states, was originally proposed as an intermediate state of some proteins with a compact conformation, a considerably native-like secondary structure, and a largely fluctuating tertiary structure [3].Secondly, the hydrogen-bonded native-like secondary structure formed in the same regions is the stable secondary structure in the native molecule. Thirdly, the native tertiary fold, already organized for part of the protein molecule, yet lacks the specific tertiary structure with rigid side-chain packing [1]. In the present study, we have investigated one of the intermediate states of milk carrier proteins of β -lactoglobilun (BLG) variants (type A and B) induced by 2,2′-bipyridinglycinato Pd(II) nitrate, hereafter referred to as the Pd(II) complex (scheme 1), at room temperature, physiologic temperature, and low- and high-grade fever temperatures. We also determine differences in the behaviors of these Pd(II)-induced molten globules of BLG-A and BLG-B.