Investigating the binding mechanism of temporin Rb with human serum albumin, holo transferrin, and hemoglobin using spectroscopic and molecular dynamics techniques

The interaction of human serum albumin (HSA), human holo transferrin (HTF), and hemoglobin (Hb) with temporin Rb (TRb) were investigated using several spectroscopic and molecular dynamics (MD) simulation approaches, and the values for the binding constant of the HSA-TRb, HTF-TRb, and Hb-TRb complexes were found to be (1.08 +/- 0.04) x 103 M- 1, (0.27 +/- 0.05) x 103 M- 1 and (0.14 +/- 0.07) x 103 M- 1 , respectively. The thermodynamic parameters were determined using fluorescence data collected at three distinct temperatures, and the negative values of Delta H0 and Delta S0 concluded that the functions of the van der Waals forces and hydrogen bonds were critical during the binding of the carrier proteins with the TRb. Synchronous fluorescence measurements provided information on the Tyr and Trp residues, and the presence of TRb was seen to change the complex structure of HSA, HTF, and Hb. The binding distances between Trp residues of HSA, HTF, and Hb were calculated, using the Forster theory of non-radioactive energy transfer, when they interacted with TRb and were found to be 2.04, 1.78, and 1.86 nm, respectively. Comparisons with the conductometry and resonance light scattering (RLS) data revealed that the HSA-HTF complex and TRb interactions were different. The efficacy of the circular dichroism (CD) technique to induce protein conformational changes was proven by the fact that the secondary structure of all three cases expanded as the TRb concentration was enhanced. The molecular modeling supported the experimental observations on the binding of the HSA-TRb, HTF-TRb, and Hb-TRb complexes, and studying the TRb interactions suggested that polar residues were essential for their stability.