Studies on the Dissociation and Urea-Induced Unfolding of FtsZ Support the Dimer Nucleus Polymerization Mechanism

• Published in: Biophysical journal Vol. 102; no. 9; pp. 2176 - 2185
• Main Authors: Montecinos-Franjola, Felipe, Ross, Justin A., Sánchez, Susana A., Brunet, Juan E., Lagos, Rosalba, Jameson, David M., Monasterio, Octavio
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02.05.2012; Biophysical Society; The Biophysical Society
• Subjects: Bacteria; Bacterial proteins; Bacterial Proteins - chemistry; Bacterial Proteins - ultrastructure; Correlation analysis; Cytokines; cytokinesis; Cytoskeletal Proteins - chemistry; Cytoskeletal Proteins - ultrastructure; Dimerization; Dimers; dissociation; Fluorescence; fluorescence emission spectroscopy; Models, Chemical; Models, Molecular; Monomers; Polymerization; Polymers - chemistry; Protein; Protein Denaturation; Protein Folding; Proteins; Self assembly; size exclusion chromatography; thermodynamics; Urea - chemistry
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2012.03.064

FtsZ is a major protein in bacterial cytokinesis that polymerizes into single filaments. A dimer has been proposed to be the nucleating species in FtsZ polymerization. To investigate the influence of the self-assembly of FtsZ on its unfolding pathway, we characterized its oligomerization and unfolding thermodynamics. We studied the assembly using size-exclusion chromatography and fluorescence spectroscopy, and the unfolding using circular dichroism and two-photon fluorescence correlation spectroscopy. The chromatographic analysis demonstrated the presence of monomers, dimers, and tetramers with populations dependent on protein concentration. Dilution experiments using fluorescent conjugates revealed dimer-to-monomer and tetramer-to-dimer dissociation constants in the micromolar range. Measurements of fluorescence lifetimes and rotational correlation times of the conjugates supported the presence of tetramers at high protein concentrations and monomers at low protein concentrations. The unfolding study demonstrated that the three-state unfolding of FtsZ was due to the mainly dimeric state of the protein, and that the monomer unfolds through a two-state mechanism. The monomer-to-dimer equilibrium characterized here (Kd = 9 μM) indicates a significant fraction (∼10%) of stable dimers at the critical concentration for polymerization, supporting a role of the dimeric species in the first steps of FtsZ polymerization.