Abstract
Monosodium glutamate (MSG) is the world’s most extensively used food additive and is generally recognized as safe according to the FDA. However, it is well reported that MSG is associated with a number of neurological diseases, and in turn, neurological diseases are associated with protein aggregation. This study rationalized the role of MSG in protein aggregation using different biophysical techniques such as absorption, far-UV CD, DLS, and ITC. Kinetic measurements revealed that MSG causes significant enhancement of aggregation of BSA through a nucleation-dependent polymerization mechanism. Also, CTAB-BSA aggregation is enhanced by MSG significantly. MSG-induced BSA aggregation also exhibits the formation of irreversible aggregates, temperature dependence, non-Arrhenius behavior, and enhancement of hydrodynamic diameter. From the isothermal titration calorimetry measurement, the significant endothermic heat of the interaction of BSA-MSG indicates that protein aggregation may be due to the coupling of MSG with the protein. The determined enthalpy change (ΔH) is largely positive, also suggesting an endothermic nature, whereas entropy change (ΔS) is positive and Gibbs free energy change (ΔG) is largely negative, suggesting the spontaneous nature of the interaction. Furthermore, even a low concentration of MSG is involved in the unfolding of the secondary structure of protein with the disappearance of original peaks and the formation of a unique peak in the far-UV CD, which is an attention-grabbing observation. This is the first investigation which links the dietary MSG with protein aggregation and thus will be very instrumental in understanding the mechanism of various MSG-related human physiological as well as neurological diseases.
Highlights
Monosodium glutamate (MSG), chemical formula C5H8NO4Na, is the sodium salt of glutamic acid and is naturally found in cheese, tomatoes, mushroom, and grapes (Jinap and Hajeb, 2010; Figure 1A)
By means of time course measurement using the UV-visible spectrophotometer, the aggregation kinetics of bovine serum albumin in the presence of dietary MSG was done by assessing the turbidity of the protein solution
The aggregation kinetics was performed on a protein solution with a fixed volume of 5 μM by titrating with different concentrations of MSG starting from 0.1 molar to 4.5 molar
Summary
Monosodium glutamate (MSG), chemical formula C5H8NO4Na, is the sodium salt of glutamic acid and is naturally found in cheese, tomatoes, mushroom, and grapes (Jinap and Hajeb, 2010; Figure 1A). There are numerous reports regarding the harmful effects of food containing excessive amounts of MSG and how it causes headache, migraine, tingling or burning in the face, sweating, facial pressure or tightness, numbness, flushing in the neck and other areas, rapid fluttering heartbeats (heart palpitations), chest pain, nausea, and weakness, according to the International Classification of Headache Disorders (ICHD), third edition. Such physiological responses are referred to as MSG symptom complex or Chinese restaurant syndrome (Yang et al, 1997)
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