An engineered minidomain containing an elastin turn exhibits a reversible temperature-induced IgG binding.
A two-helix version of the triple alpha-helical staphylococcal Protein A, previously shown to retain the Fc binding properties of protein A, has been engineered to contain an elastin sequence, GVPGVG, within the inter-helix turn. The original type I beta-turn was replaced with a beta-turn from the muscle protein elastin, which has an inverse temperature-induced folding transition. These "elastin mutants" had lost their helical structure, as measured by circular dichroism (CD), and exhibited a lower stability than the wild-type domains (T(m) reduced by about 48 degrees C) in 30% trifluoroethanol. For the wild-type domains, the amount of alpha-helix and the binding affinity for Fc decreased as the temperature was increased. In contrast, although the starting affinity was lower for the disulfide elastin-turn mutant, it exhibited a 21-fold improvement in affinity over the same temperature range. The melting curve for the elastin-turn minidomain showed cooperative behavior, as measured by the increase in CD-amplitude at 222 nm. The observed CD behavior is consistent with the formation of a type I beta-turn, exhibiting similar DeltaH and DeltaS values to those seen previously for short elastin peptides [Reiersen, H., Clarke, A. R., and Rees, A. R. (1998) J. Mol. Biol. 283, 255-264], and accounting for the increase in on-rate. This demonstrates that, when inserted into a stable globular protein, short elastin sequences have the ability to modify local structure and activity, by operating as temperature modulated switches.
Reiersen
H
H
Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
Rees
A R
AR
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004549:Elastin / Q000737:chemistry* / Q000378:metabolism*; D007074:Immunoglobulin G / Q000378:metabolism*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D015202:Protein Engineering; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics
D007074:Immunoglobulin G; D004549:Elastin