External cavity-quantum cascade laser infrared spectroscopy for secondary structure analysis of proteins at low concentrations

ALACARÁZ, M; SCHWAIGHOFER A; ARAMAN; GOICOECHEA, H; LENDL B

Scientific Reports

Springer Nature

Año: 2016 vol. 6

Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy are analytical techniquesemployed for the analysis of protein secondary structure. The use of CD spectroscopy is limited tolow protein concentrations (5 mg ml−1). Here we introduce a quantum cascade laser (QCL)-based IRtransmission setup for analysis of protein and polypeptide secondary structure at concentrationsas low as 0.25 mg ml−1 in deuterated buffer solution. We present dynamic QCL-IR spectra of thetemperature-induced α-helix to β-sheet transition of poly-L-lysine. The concentration dependence ofthe α-β transition temperature between 0.25 and 10 mg ml−1 was investigated by QCL-IR, FTIR andCD spectroscopy. By using QCL-IR spectroscopy it is possible to perform IR spectroscopic analysis inthe same concentration range as CD spectroscopy, thus enabling a combined analysis of biomoleculessecondary structure by CD and IR spectroscopy.