Effects of the Environment on the Structure of Adsorbed Proteins: Fourier Transform Infrared Spectroscopic Studies

Abstract

The protein backbone vibrations have been assigned for a group of proteins in aqueous solution using deconvoluted spectra for the assignments. These assignments were related to the secondary structure of the proteins and show the effect of one secondary structure on another. Changes in the environment of dissolved and adsorbed proteins have been followed by infrared spectroscopy and these spectral changes have been used to verify the vibrational assignments and determine the secondary structures. Very few of the infrared studies of proteins have been carried out on aqueous solutions of the proteins. Except for the work ofKoenig and Tabb (1), the few aqueous IR studies have been on single proteins. Correspondingly, most of the assignments of the backbone vibrations (the so-called Amide I, II, III, etc. vibrations) have been based on either Raman spectra of aqueous solutions (2) or on infrared spectra of proteins in the solid state (3). Where infrared solution spectra have been obtained, it has mostly been on D2O solutions (4) -not H2O solutions. Since these Amide I, II, III, etc. vibrations involve motion of the protein backbone, they are sensitive to the secondary structure of the protein and thus valid assignments are necessary in order to use infrared spectroscopy for determining the conformations of proteins.The Raman frequencies of the protein backbone vibrations are often different than the infrared frequencies and thus infrared assignments are needed for structure determinations from infrared spectra.Such structural information is needed from the 'Current address: Mattson Instruments, Inc., 1001 Fourier Court, Madison, WI 53717

The Ex Vivo Effect of Preadsorbed Vitronectin on Platelet Activation

“…A similar looking compositeamide I band has been observed for the deconvoluted structure of ovalbumin (27). The bands at 1,638 and 1,682 cm -1 can be attributed to (3-sheet structure, while the band at 1,655 cm -1 may be assigned to random or a-helix structures, respectively (28,29).…”

“…The band at 1,520-1,523 cm" 1 is rather unusual as the amide II region typically displays one peak centered at 1,550 cm" 1 . However, ribonuclease A, a protein with nearly equal amounts of a-helix and (3-sheet structure, does show evidence of both of these peaks in the amide II region (28). This, as of yet unassigned, 1,520-1,523 cm" 1 peak seems more dominant for the adsorption of VN to PTMO-PU than to SR.…”

“…For PTMO-PU, the spectra are much different between 1,230 and 1,300 cm \ A large peak at 1,275 cm" 1 is present which was totally absent from the SR spectra. Both infrared and Raman studies have suggested that a-helix proteins absorb between 1,260 and 1,290 cm l in the amide III region and that random and unstructured polypeptides absorb from 1,235 to 1,265 cm" 1 (28,(31)(32)(33). Thus, as compared to solution VN, adsorbed VN on PTMO-PU may be developing some a-helix structure.…”

Formation of stable polypeptide monolayers at interfaces: controlling molecular conformation and orientation

“…In the present study we investigated the formation and structural properties of peptide assemblies at different interfaces, using either amphipathic or hydrophobic polypeptide helices. The stable helix structure of both polypeptides in organic solution and bulk solids was found to be unchanged in monolayers at the air/water and air/solid interfaces, in contrast to the often observed phenomenon that water-soluble proteins and polypeptides denature at the air/ water interface or upon contact with the support (Jakobsen and Wasacz, 1987;Jakobsen et al, 1985;MacRitchie, 1987;Smith and Clark, 1992). To our knowledge, RA-FTIR measurements were used for the first time to deliver direct experimental evidence for the molecular conformation of pure peptide monolayers.…”

Lyophilization-induced reversible changes in the secondary structure of proteins.

“…This is because although the FTIR bands in the amide I region directly correspond to these secondary structural elements (16,17), the line broadening in the spectra of lyophilized proteins, combined with strongly overlapping bands, make such quantitation in this region arduous (15,18). Another spectral region, the amide III band (1220-1330 cm-'), also reflects the secondary structure of proteins (19)(20)(21) and has been used to characterize structural changes qualitatively (22)(23)(24)(25)(26) and, in aqueous solution, even to quantify the individual secondary structure composition of proteins (19)(20)(21)27). …”