Conserved and nonconserved features of the folding pathway of hisactophilin, a beta-trefoil protein.
Based on previous studies of interleukin-1beta (IL-1beta) and both acidic and basic fibroblast growth factors (FGFs), it has been suggested that the folding of beta-trefoil proteins is intrinsically slow and may occur via the formation of essential intermediates. Using optical and NMR-detected quenched-flow hydrogen/deuterium exchange methods, we have measured the folding kinetics of hisactophilin, another beta-trefoil protein that has < 10% sequence identity and unrelated function to IL-1beta and FGFs. We find that hisactophilin can fold rapidly and with apparently two-state kinetics, except under the most stabilizing conditions investigated where there is evidence for formation of a folding intermediate. The hisactophilin intermediate has significant structural similarities to the IL-1beta intermediate that has been observed experimentally and predicted theoretically using a simple, topology-based folding model; however, it appears to be different from the folding intermediate observed experimentally for acidic FGF. For hisactophilin and acidic FGF, intermediates are much less prominent during folding than for IL-1beta. Considering the structures of the different beta-trefoil proteins, it appears that differences in nonconserved loops and hydrophobic interactions may play an important role in differential stabilization of the intermediates for these proteins.
Liu
Chengsong
C
Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada.
Gaspar
Joe A
JA
Wong
Hannah J
HJ
Meiering
Elizabeth M
EM
D002352:Carrier Proteins / Q000737:chemistry*; D002942:Circular Dichroism; D007700:Kinetics; D008840:Microfilament Proteins; D008958:Models, Molecular; D017510:Protein Folding; D015800:Protozoan Proteins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D002352:Carrier Proteins; D008840:Microfilament Proteins; D015800:Protozoan Proteins; C058561:hisactophilin protein, Protozoan