Effects of temperature and chromium (III) ion on the structure of bovine b-Lactoglobulin-A

Abstract

Estudos termodinâmicos relativos ao efeito da temperatura (de 27 a 47 ºC) sobre a estrutura da b-lactoglobulina-A bovina (BLG-A), em solução de cloreto de sódio 50 mmol L -1 , na presença e ausência de íons Cr(III), usando espectroscopia de absorção no UV-Visível, dicroísmo circular (DC), próximo e distante e, espectroscopia de fluorescência, foram realizados. Os estudos com CD UV-distante, a diferentes temperaturas e na presença e ausência de íons Cr(III) não mostraram alteração significativa na estrutura secundária da proteína. Ao contrário, os estudos empregando DC UV-próximo evidenciaram alterações na estrutura terciária da BLG natural com o aumento da temperatura, indicada pela exposição de fragmentos de tirosina (Tyr). Estudos de espectroscopia de fluorescência em BLG-A natural, na ausência e presença de íons Cr(III) apresentam considerável alteração na estrutura terciária da proteína, devido ao aumento da temperatura. Com a estabilização da proteína na presença de íons Cr(III), a estrutura terciária da BLG revela considerável alterações a 37 e 47 °C as quais são concordantes com o aumento nos valores de T m nestas temperaturas.Thermodynamic studies of the effect of temperature (27-47 ºC) on the structure of bovine b-lactoglobulin-A (BLG-A) in the absence and presence of Cr(III) containing 50 mmol L -1 sodium chloride have been carried out using UV-Visible absorption spectroscopy, far and near circular dichroism (CD) and fluorescence spectroscopy. The far-UV CD studies do not show any significant change in the secondary structure of the protein at different temperatures in the absence and presence of Cr(III). On the contrary, the near-UV CD studies show change in the tertiary structure of the native BLG on increasing the temperature, indicating the exposure of Tyr residues. Fluorescence spectroscopic studies on the native BLG-A in the absence and presence of Cr(III) represent considerable change in the tertiary structure of the protein due to the increase in temperature. Due to protein stabilization in the presence of Cr(III) ions, the tertiary structure of BLG represents considerable alterations at 37 and 47 ο C that is in agreement with increasing of T m values at these temperatures.Keywords: b-lactoglobulin, temperature, Cr(III) ions, tertiary structure, T m value IntroductionWhey protein products are important food ingredients because of their desirable functional properties such as gelation and emulsification. The major proteins in these whey protein products are a-lactalbumin (a-La; 20%) and b-lactoglobulin (BLG; 50%). 1 b-Lactoglobulin is a small water-soluble protein that forms the major component of ruminant milk whey. 2 Seven different genetic variants have been identified but in industrial preparations A and B variants are the most prevalent. Variant A (BLG-A) differs in amino acid sequence from variant B (BLG-B) at positions 64 (Asp A →Gly B ) and 118 (Val A → Ala B ). 3 These differences result in distinct biophysical and biochemical properties of the variants such as heat stability, self-asso...

Immunogenic and structural properties of ovalbumin treated by pulsed electric fields

“…The residue of tryptophan is mainly responsible for the near-UV region. [31] As shown in Figure 5, the UV absorption intensity at 279 nm was enhanced after PEF processing. When treated for 180 µs, it increased gradually with increasing strength, reaching the maximum absorption at 25 kV/cm.…”

High‐intensity ultrasound enhances the immunoglobulin (Ig)G and IgE binding of ovalbumin

“…The UV absorbance of protein in the near‐UV region depends on the residues of the aromatic amino acids, including tryptophan, tyrosine and phenylalanine, with tryptophan being mainly responsible for the near‐UV region . The effect of ultrasound treatment on the UV absorption spectra of OVA is shown in Fig.…”

Comparative study on the effects of nystose and fructofuranosyl nystose in the glycation reaction on the antigenicity and conformation of β-lactoglobulin

“…Circular dichroism (CD) spectroscopy analyses were run for different b-LG samples according to Divsalar, Saboury, Ahmad, and Moosavi-Movahedi (2009). Far-UV CD spectra of b-LG at 0.1 mg/mL in 10 mM sodium phosphate buffer, pH 7.0, were collected at 22°C using a MOS-450 spectropolarimeter (French Bio-Logic SAS Co., Claix, French).…”