A Second Look at Mini-Protein Stability: Analysis of FSD-1 Using Circular Dichroism, Differential Scanning Calorimetry, and Simulations

• Published in: Biophysical journal Vol. 97; no. 10; pp. 2803 - 2810
• Main Authors: Feng, Jianwen A., Kao, Jeff, Marshall, Garland R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.11.2009; Biophysical Society; The Biophysical Society
• Subjects: Amino acids; Calorimetry, Differential Scanning; Circular Dichroism; Computer Simulation; Dichroism; Differential scanning calorimetry; DNA-Binding Proteins - chemistry; Folding; Hydrogen Bonding; Melting; Models, Chemical; Models, Molecular; Molecular dynamics; Molecular structure; Phase Transition; Protein; Protein Folding; Protein Stability; Protein Structure, Secondary; Proteins; Simulation; Stability; Temperature; Transcription Factors - chemistry; Transition Temperature; Zinc
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2009.08.046

Mini-proteins that contain <50 amino acids often serve as model systems for studying protein folding because their small size makes long timescale simulations possible. However, not all mini-proteins are created equal. The stability and structure of FSD-1, a 28-residue mini-protein that adopted the ββα zinc-finger motif independent of zinc binding, was investigated using circular dichroism, differential scanning calorimetry, and replica-exchange molecular dynamics. The broad melting transition of FSD-1, similar to that of a helix-to-coil transition, was observed by using circular dichroism, differential scanning calorimetry, and replica-exchange molecular dynamics. The N-terminal β-hairpin was found to be flexible. The FSD-1 apparent melting temperature of 41°C may be a reflection of the melting of its α-helical segment instead of the entire protein. Thus, despite its attractiveness due to small size and purposefully designed helix, sheet, and turn structures, the status of FSD-1 as a model system for studying protein folding should be reconsidered.