DETERMINATION OF THE CONFORMATION OF SPECIFIC RESIDUES IN A MODEL PEPTIDE BY <super>13</super>C ISOTOPE-EDITED ATR-FTIR IN REGULAR WATER

Abstract

Determination of protein structures has attracted extensive scientific attention. IR spectroscopy using traditional liquid cells has been reported to address the structure in a model peptide of sequence Ac-YAAKAAAKAAAAKAAH-NH₂ (pep17) with <super>13</super>C isotopic labels in deuterated water (D₂O). Although similar to regular water, D₂O is not physiologically equivalent to H₂O in the aqueous matrix of cells and tissues. Therefore, peptide studies in D₂O may not yield true peptide conformations. Here, <super>13</super>C isotope-edited FTIR was applied on pep17 in H₂O using the Attenuated Total Reflection (ATR) technique. The peak of <super>13</super> C labeled residues in &#945;-helix appears at 1602 cm<super>-1</super>, which can be used as a fingerprint peak of &#945;-helix for the <super>13</super>C labeled residue. By the presence or absence of peak at 1602 cm<super>-1</super>, conformation of specific residues in the peptide was determined. For the first time, the elucidation of the secondary structure of the pep17 has been demonstrated in H₂O.