New insight into the pH‐dependent conformational changes in bovine β‐lactoglobulin from Raman optical activity

Abstract

Abstract:We have studied the conformation of b-lactoglobulin in aqueous solution at room temperature over the pH range ;2.0-9.0 using vibrational Raman optical activity~ROA!. The ROA spectra clearly show that the basic up and down b-barrel core is preserved over the entire pH range, in agreement with other studies. However, from the shift of a sharp positive ROA band at ;1268 to ;1294 cm Ϫ1 on going from pH values below that of the Tanford transition, which is centered at pH ;7.5, to values above, the Tanford transition appears to be associated with changes in the local conformations of residues in loop sequences possibly corresponding to a migration into the a-helical region of the Ramachandran surface from a nearby region. These changes may be related to those detected in X-ray crystal structures which revealed that the Tanford transition is associated with conformational changes in loops which form a doorway to the interior of the protein. The results illustrate how the ability of ROA to detect loop and turn structure separately from secondary structure is useful for studying conformational plasticity in proteins.

Redox‐Active Chiroptical Switching in Mono‐ and Bis‐Iron Ethynylcarbo[6]helicenes Studied by Electronic and Vibrational Circular Dichroism and Resonance Raman Optical Activity

“…ROA measures the difference of the Ramans cattered intensity between right and left circularly polarization and has become one of the prime techniques for determining absolute configurations of molecules [17][18][19][20] and conformers of biomolecules [21,22] in addition to ECD, VCD, andOR. [23,12] Quantum-mechanical calculationsa re very important for the assignment of ROA spectra, for instance, to assign the absolute configuration of chirally deuterated neopentane [24] and methyloxiranei ng as and liquid phases, [25,26] or the asymmetricc arboni nC HFClBr.…”

Raman optical activity study on insulin amyloid‐ and prefibril intermediate

“…Interestingly, a b-barrel protein, bovine b-lactoglobulin under pH 2.0 or 6.8, showed a positive ROA peak at 1268 cm 21 . 61 It was suggested that this peak originated from the type-I b-turn or inverse g-turn, but not so clear. This peak vanished under the alkalic pH, 61 suggesting a relation to the structural changes of turns and loops associated with the Tanford transition.…”

Characterisation and use of β-lactoglobulin fibrils for microencapsulation of lipophilic ingredients and oxidative stability thereof

“…In native systems, when comparing pH 2.0 with 3.0 a considerable increase in interfacial viscoelastic modulus and its elastic part as well as a concurrent decrease in phase angle from 18.0°to 5.7°w as observed (p < 0.05) at the higher pH value. With a change in pH from 2.0 to 3.0 the quaternary structure of b-lactoglobulin changes from predominantly monomeric to dimeric, respectively (Blanch et al, 1999;Taulier and Chalikian, 2001) and is accompanied by a change in surface density of adsorbed proteins explaining the significant differences in IFT (Table 1). Regarding the fibrils, notable differences in dilatational elastic moduli E 0 between short and long fibrils were observed at pH 2.0 and 3.0.…”