Generality and specificity of the binding behaviour of lysozyme with pectin varying in local charge density and overall charge

Abstract

We examined the similarities and differences of the binding behavior of lysozyme (lys) with pectin varying in local charge density (blockwise distribution and statistical distribution of methoxyl groups, BP and SP) and similar degree of methoxylation (DM). The interaction at ionic strength I=0.01 and pH 5.1 was found to be mainly electrostatic, associated with an exothermic enthalpy change. BP which is more inclined to self-association binds lys forming strongly associated complex particles with average sizes much larger (10-20 µm) than that of SP. The latter formed with lys small (0.6-3 µm) complex particles or liquid droplets depending on DM. The critical Iset and pHset values for BP/lys systems, above which complexes do not form, are not sensitive to DM (approximately 0.1 and 11.5 respectively), whereas for SP/lys systems the critical Iset and pHset values decrease significantly with increasing DM. The effect of I on complexation (CP) of lys with BP and SP has a nonmonotonic character. The distribution of BP and SP within the complex particles is irregular and is different for pectin with low and high DM values. The binding constant and stoichiometry ratio (lys/pectin) of the systems with SP are slightly higher than those of BP at the same DM, and these values decrease sharply (50 times) with increasing DM. The large positive changes in entropy in SP/lys systems suggest that the interactions in these systems tend to be more hydrophobic in character at high DM. On the other hand, with BP, a negative enthalpy change, especially for pectin with low charge, suggests the formation of a large quantity of hydrogen bonds or van der Waals interactions during CP.

Complex coacervation of pea albumin‐pectin and ovalbumin‐pectin assessed by isothermal titration calorimeter and turbidimetry

“…Unlike the results of Girard et al ., 23 P29 and P90 behaved differently with PA in the ITC studies. The ΔH and ΔS values were lower for PA‐P29 than PA‐P90 (Table 1).…”

“…Note that the K value is higher for PA‐P29 admixtures (P29 with higher GalA content) than PA‐P90. This was previously observed in ovalbumin‐CMC 25 and in a β ‐lactoglobulin‐pectin 23 system. The impact of DB on the thermodynamic parameters is better understood by comparing the current study with the previously reported pea protein isolate (PPI)‐pectin interaction by Lan et al .…”

“…The ΔH , ΔS and ΔG for all PA‐pectin admixtures were negative indicating that the complexing in these systems was dominated by enthalpy change. Girard et al 23 . has investigated the effect of high methoxy and low methoxy pectin on complexation with β ‐lactoglobulin to determine its thermodynamic parameters.…”

“…Pectin is an anionic polysaccharide that is widely used by the food industry as a thickener and gelling agent 19‐21 . The unique arrangement of non‐methyl α ‐(1‐4)‐linked d ‐galacturonic acid (GalA) in blocks – which gives the degree of blockiness (DB) – and the number of methyl esterified galacturonic acids – which gives the degree of methyl esterification (DE) – control their complexation to proteins 22, 23 . A previous study conducted on β ‐lactoglobulin‐high methoxy / low methoxy pectin indicated that the degree of methyl esterification of pectin has no effect on the binding enthalpy 24, 25 .…”

Heteroprotein Complex Coacervate Based on β-Conglycinin and Lysozyme: Dynamic Protein Exchange, Thermodynamic Mechanism, and Lysozyme Activity

“…The entropy gain (Δ S ) from the release of counterions and water can even overcome the enthalpic contribution of electrostatic interaction. However, in some protein/polysaccharide systems, enthalpy change (Δ H ) was more dominant. − Therefore, we determine the thermodynamics of β-CG/LYS complexation using isothermal titration calorimetry (ITC) to understand the balance between Δ S and Δ H during HPCC and the thermodynamic nature behind β-CG/LYS interaction (Figure ).…”