Molecular Dynamics of Psychrophilic Enzyme Mutants Figure 6. Salt bridges clusters in wild-type AHA and PPA simulations. The salt bridges are mapped on the 3D average structures from simulation as sticks connecting the Ca atoms for AHA and PPA. The white dot and spheres indicate the location of the coordinated ions. The different clusters of spatial proximity of the salt-bridges and their networks are indicated by different colors (blue, lightblue, cyan, palecyan, purple, violet, pink, green, dark green and white for clusters 1,2,3,4,5,6,7,8,9 and 10, respectively). A detailed list of the salt bridges is reported in Table S1 (in Supporting Information S1). doi:10.1371/journal.pone.0024214.g006 correlated motions (involving residues E10P, W11P, T71P, R72P, S73P, G74P, N75P) in PPA (Figure 8B) and it is related to the highest flexibility scattered toward solvent-exposed regions of L8 loop and therefore, to the different local dynamic fingerprint with respect to AHA. The correlation cluster mediated by I367P and the aforementioned PPA salt bridge network cannot be established in AHA or AHA mutants since I367P is located in the L8 insertion typical of mesophilic amylases (Figure S9 in Supporting Informa- tion S1) and R343P, D381P and K368P are replaced by D306A, N332A and V318A, respectively. Interestingly, in the AHA Figure 7. Salt bridge clusters in AHA mutants - part I. The salt bridges are mapped on the 3D average structures from simulation as sticks connecting the Ca atoms for AHASS, AHAVF, AHATV, AHANR, AHAQI, AHA5SS and AHA5. Salt-bridges of wild-type AHA are reported as a reference. (nota: meglio rimandare alla legenda di figura 6?) The white dots and spheres indicate the location of the coordinated ions. The different clusters of spatial proximity of the salt-bridges and their networks are indicated by different colors (blue, lightblue, cyan, palecyan, purple, violet, pink, green, dark green and white for clusters 1,2,3,4,5,6,7,8,9 and 10, respectively). A detailed list of the salt bridges is reported in Table S1 (in Supporting Information S1). doi:10.1371/journal.pone.0024214.g007 PLoS ONE | www.plosone.org 7 September 2011 | Volume 6 | Issue 9 | e24214