The bZIP Region of the Plant Transcription Factor Opaque-2 Forms Stable Homodimers in Solution and Retains Its Helical Structure upon Subunit Dissociation
详细信息 查看全文
- 作者：Vitor Hugo Moreau ; Alba C. da Silva ; Rodrigo M. P. Siloto ; Ana Paula Valente ; Adilson Leite ; and Fá ; bio C. L. Almeida
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：April 27, 2004
- 年：2004
- 卷：43
- 期：16
- 页码：4862 - 4868
- 全文大小：116K
- 年卷期：v.43,no.16(April 27, 2004)
- ISSN：1520-4995
文摘
Opaque-2 (O2) is a plant bZIP transcription factor that regulates the expression of 
fchars/alpha.gif" BORDER=0> and fchars/beta2.gif" BORDER=0 ALIGN="middle">prolamines, the main storage proteins in seeds of cereals such as maize and Coix. One of the main processesmodulating O2 activity is the heterodimerization with other bZIP transcription factors, but the primarymechanism underlying the partner choice is still unknown. In this paper, we have characterized the bZIPdomain of O2 by nuclear magnetic resonance (NMR), circular dichroism (CD), and size-exclusionchromatography. Results obtained from CD measurements suggested that the native O2bZIP has about40 of its 49 leucine-zipper residues in helical structure, while the DNA-binding domain is completelyunstructured. Diffusion-ordered NMR spectroscopy and size-exclusion chromatography showed that O2forms homodimers in solution. Thermal denaturation experiments indicate that O2 reversibly undergoesdissociation and unfolding in a process that is fully dependent on the protein concentration. Subunitdissociation of O2bZIP dimers, upon dilution of the protein, led to partially folded monomers that retained~80% of the native CD ellipticity at 222 nm. We believe that the existence of partially folded monomerscould decrease the entropic penalty for helix formation involved in the DNA binding and in the subunitassociation of O2bZIP. Stabilization of partially folded monomers may also play a significant role in thedimerization of O2 with other bZIP transcription factors and, consequently, can be important for theregulation of the biological functions of O2 in plants.
fchars/alpha.gif" BORDER=0> and fchars/beta2.gif" BORDER=0 ALIGN="middle">prolamines, the main storage proteins in seeds of cereals such as maize and Coix. One of the main processesmodulating O2 activity is the heterodimerization with other bZIP transcription factors, but the primarymechanism underlying the partner choice is still unknown. In this paper, we have characterized the bZIPdomain of O2 by nuclear magnetic resonance (NMR), circular dichroism (CD), and size-exclusionchromatography. Results obtained from CD measurements suggested that the native O2bZIP has about40 of its 49 leucine-zipper residues in helical structure, while the DNA-binding domain is completelyunstructured. Diffusion-ordered NMR spectroscopy and size-exclusion chromatography showed that O2forms homodimers in solution. Thermal denaturation experiments indicate that O2 reversibly undergoesdissociation and unfolding in a process that is fully dependent on the protein concentration. Subunitdissociation of O2bZIP dimers, upon dilution of the protein, led to partially folded monomers that retained~80% of the native CD ellipticity at 222 nm. We believe that the existence of partially folded monomerscould decrease the entropic penalty for helix formation involved in the DNA binding and in the subunitassociation of O2bZIP. Stabilization of partially folded monomers may also play a significant role in thedimerization of O2 with other bZIP transcription factors and, consequently, can be important for theregulation of the biological functions of O2 in plants.