Effect of aggregation on hydration of HSA protein: Steady-state Terahertz absorption spectroscopic study

• Published in: Journal of chemical sciences (Bangalore, India) Vol. 132; no. 1
• Main Authors: Manna, Biswajit, Nandi, Amitabha, Tanaka, Masahito, Toyokawa, Hiroyuki, Kuroda, Ryunosuke, Palit, Dipak K
• Format: Journal Article
• Language: English
• Published: New Delhi Springer India 01.12.2020; Springer Nature B.V
• Subjects: Absorbance; Absorption; Agglomeration; Aggregates; Aqueous solutions; Buffer solutions; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Frequency ranges; Hydration; Monomers; Photon correlation spectroscopy; Proteins; Regular Article; Serum albumin; Terahertz frequencies; Thickness; nonlinear increase of THz absorption with concentration; hydration layer; Steady-state terahertz absorption spectroscopy; human serum albumin in aqueous solution; protein aggregation at high protein concentration
• ISSN: 0974-3626; 0973-7103
• DOI: 10.1007/s12039-019-1696-4

Terahertz (THz) absorption behaviour of HSA protein in aqueous buffer solutions has been investigated in the 0.1–2 THz frequency range using a highly intense THz source based on coherent transition radiation (CTR) generated using a femtosecond electron accelerator of 42 MeV energy (for 0.3–2 THz) and a klystron (at 0.1 THz). Like in the cases of other proteins reported earlier, THz absorbance of the protein solutions follow nonlinear behaviour with increasing concentration of HSA protein monitored through the entire frequency range. THz absorbance of the solution initially increases to follow an apparently linear behaviour up to the concentration of ~6 × 10 −4 mol dm −3 but decreases gradually with further increase in HSA concentration. The linear behaviour in low concentration regime could be explained considering the increase in concentration of the monomer HSA molecules in solution with a well-defined hydration layer of thickness of about 22 Å around it. However, the study of dynamic light scattering measurements suggest the presence of increasing number of protein aggregates in solution with increasing concentration of protein. THz absorbance of each of these samples could be calculated to show that absorbance decreases with increasing number of aggregates in solution and also the relative concentrations of the monomer and aggregated particles existing in solutions could be estimated. This work, for the first time, explains the nonlinear change in THz absorbance of protein solutions with increasing protein concentration considering the protein aggregation effect at very high concentration. Graphical Abstract At low concentration of Human Serum Albumin protein in aqueous solution, each monomer protein molecule is surrounded by a hydration layer of about 2.2 nm thick.