Interactions Of Fatty Acid Salt With Bovine Serum Albumin In Crowing Environment

As an essential energetic material of the organism,fatty acids are classified into short chain,medium chain and long chain according to different carbon chain lengths.Serum albumin is the main transporter of fatty acids in the body.Different type and structures of fatty acids have different binding mechanism with serum albumin.Thereby the physiological and biochemical reactions of organism have different influence.Therefore,a systematic study towards fatty acids binding mechanisms with serum albumin has important physiological significance on the understanding of how fatty acid is transported in the body.However,the previous studies about fatty acids and serum albumin were conducted in weak solution,the study of interaction between fatty acid and serum albumin in crowded environment is few.In this paper,PEG in different concentrations and molecular weights and Dextran20 are adopted to simulate macromolecular crowding environment in the body;Isothermal Titration Calorimetry(ITC)and Steady-state Fluorescence Spectrum(FL)are used to investigate the interactions between bovine serum albumin(BSA)and fatty acids salt(Na-FA)in different chain lengths;Differential Scanning Calorimetry(DSC)and Circular Dichroism(CD)are used to investigate the influence of Na-FA on BSA secondary structure and thermodynamic stability in crowding environment.The main research contents in this paper include:(1)A study of interactions between BSA and Na-FA in different chain lengths in PEG2000 crowding environment.The research shows that the binding form of short chain Na-FA and BSA gradually transits from the combination of one site to the combination of two sites,and the binding constant(K)of sodium caprylate(C8),pelargonic acid sodium(C9)and sodium caprate(C10)higher in PEG2000 than that of dilute solution.However the K of BSA and Sodium laurate(C12),sodium oleate(C18:1),linoleic acid sodium(C18:2)in PEG2000 were less than dilute solution.It can be seen from thermodynamic parameter that negative synergistic effect exists in the process of the combination between saturated Na-FA and BSA,and the main effect is electrostatic interaction;positive cooperativity exists in the process of the combination between unsaturated Na-FA and BSA,and the main effects are electrostatic force and Van der Waals’ force.In PEG2000,phase-transition temperature(Tm)of BSA decreases.When Na-FA is added,increases the Tm of BSA.The Tm of BSA with C8,C9 and C10 are greater than pure BSA that there exists positive cooperativity.C12,C18:1 and C18:2 make the Tm of BSA less than pure BSA that they can’t counteract the crowded environment’s influence on phase-transition temperature of BSA in crowded environment of any concentration.(2)A study of interactions between Na-FA and BSA in other types of macromolecular crowding environments.The research result shows that combination modes of short chain Na-FA in PEG200 and PEG20000 are different from its combination mode in Dextran20.In the crowding environments with same PEG concentration,K and enthalpy change values(△H)of BSA and C8,C9 are greater than that in Dextran20,while the combination modes of C10 and C12 in PEG and Dextran20 present asymmetric "U"-shaped curve.Furthermore,the combination types and combination modes of BSA and C18:1 and C18:2 are almost not influenced by crowding environment,and crowding environment only affects AH in the combination process.The thermodynamic stability and structure of BSA shows that crowding environment results in the decrease of helix content in BSA structure,the addition of Na-FA increases its helix content and makes its structure more compact.Tm increases of BSA with the increase of carbon chain length,this means Na-FA makes structure of BSA more steady,and there is synergistic effect between them.