The conformational dynamics of xylanase A from Streptomyces lividans (Sl-XlnA) were studied using Molecular Dynamics (MD) simulation to identify the thermally sensitive regions. Sl-XlnA begins to unfold at loop4 and this unfolding expands to the loops near the N-terminus. The high flexibility of loop6 during the 300 K simulation is related to its function. The intense movements of the 3₁₀-helices also affect the structural stability. The interaction between the α4β5-loop and the neighboring α5β6-loop plays a crucial role in stabilizing the region from the α4β5-loop to α6. The most thermally sensitive region is from β3 to loop4. The high mobility of the long loop4 easily transfers to the adjacent β4 and α4 and causes β4 and α4 to fluctuate. And, salt bridges ASP124-ARG79, ASP200-ARG159, and ASP231-LYS166 formed a “clamp” to stabilize the region including α4, β4, β5, β6, and β7. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 594–604, 2013.

Iron superoxide dismutase (Fe-SOD) is predominantly found in bacteria and mitochondria. The thermal stability of Fe-SOD from different sources can vary dramatically. We have studied the influence of structural parameters on Fe-SOD thermostability by principal component analysis (PCA). The results show that an increased α-helical and turn content, an increased α-helix and loop length, an increase in the number of main-main chains and charged-uncharged hydrogen bonds, a decrease in the 3₁₀-helix content, and a decreased β-strand and loop length are all important factors for Fe-SOD thermostability. Interestingly, the use of charged residues to form salt bridges is tendentious in thermophilic Fe-SOD. Negatively charged Arg and positively charged Glu are efficiently used to form salt bridges. The cooperative action of the exposed area, the hydrogen bonds, and the secondary structure plays a crucial role in resisting high temperatures, which demonstrates that the increased stability of thermophilic Fe-SOD is provided by several structural factors acting together. © 2012 Wiley Periodicals, Inc. Biopolymers 97:864–872, 2012.