title: Temperature-induced formation of a non-native intermediate state of the all beta-sheet protein CD2.
abstract: Domain 1 of the cell adhesion protein CD2 (CD2-1) has an all beta-structure typical of proteins belonging to the immunoglobin superfamily. It has a remarkable ability to fold as a native monomer or a metastable intertwined dimer. To understand the origin of structural rearrangements of CD2-1, we have studied equilibrium unfolding of the protein using various biophysical spectroscopic techniques. At temperatures above approx 68 degrees C, a partially folded state of CD2-1 (H state) with a distinct secondary structure, involving largely exposed aromatic and hydrophobic residues and a substantially perturbed tertiary structure, is observed. In contrast, an unfolded state (D state) of CD2-1 with random-coil-like secondary and tertiary structures is observed in 6 M GuHCl. This partially folded high-temperature state has increased negative molar ellipticity at 222 nm in far-ultraviolet CD spectra, implying formation of a non-native helical conformation. The existence of this non-native high-temperature intermediate is consistent with relatively high intrinsic helical propensities in the primary sequence of CD2-1. This conformational flexibility may be important in the observed domain swapping of CD2-1.
authors.affiliation: Department of Chemistry, Center of Drug Design, Georgia State University, Atlanta 30303, USA. chejjy@panther.gsu.edu
authors.forename: Jenny J
authors.initials: JJ
authors.lastname: Yang
authors.forename: Haidong
authors.initials: H
authors.lastname: Yang
authors.forename: Yiming
authors.initials: Y
authors.lastname: Ye
authors.forename: Harry
authors.initials: H
authors.lastname: Hopkins
authors.forename: Gary
authors.initials: G
authors.lastname: Hastings
mesh_terms: D000817:Anilino Naphthalenesulfonates / Q000494:pharmacology; D000818:Animals; D018801:CD2 Antigens / Q000737:chemistry*; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D005456:Fluorescent Dyes; D005822:Genetic Vectors; D007259:Infrared Rays; D010957:Plasmids / Q000378:metabolism; D011487:Protein Conformation; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D012549:Schistosoma japonicum / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014466:Ultraviolet Rays
chemical_list: D000817:Anilino Naphthalenesulfonates; D018801:CD2 Antigens; C465878:Cd2 protein, rat; D005456:Fluorescent Dyes; C027132:1-anilino-8-naphthalenesulfonate