Effect of secondary structure on the conformations and folding behaviors of protein-like chains

Translocation of a Polymer through a Crowded Channel under Electrical Force

The translocation of a polymer chain through a crowded cylindrical channel is studied using the Langevin dynamics simulations. The influences of the field strength F, the chain length N, and the crowding extent ρ on the translocation time are evaluated, respectively. Scaling relation τ ~ F^−α is observed. With the crowding extent ρ increasing, the scaling exponent α becomes large. It is found that, for noncrowded channel, translocation probability drops when the field strength becomes large. However, for high-crowded channel, it is the opposite. Moreover, the translocation time and the average translocation time for all segments both have exponential growth with the crowding extent. The investigation of shape factor 〈δ〉 shows maximum value with increasing of the number of segments outside s. At last, the number of segments inside channel N_in in the process of translocation is calculated and a peak is observed. All the information from the study may benefit protein translocation.

A comparative study of the second-order hydrophobic moments for globular proteins: the consensus scale of hydrophobicity and the CHARMM partial atomic charges

In this paper, the second-order hydrophobic moment for fifteen globular proteins in 150 nonhomologous protein chains was performed in a comparative study involving two sets of hydrophobicity: one selected from the consensus scale and the other derived from the CHARMM partial atomic charges. These proteins were divided into three groups, based on their number of residues (N) and the asphericity (δ). Proteins in Group I were spherical and those in Groups II and III were prolate. The size of the proteins is represented by the mean radius of gyration (R_g ), which follows the Flory scaling law, R_g ∝ N^ν. The mean value of v was 0.35, which is similar to a polymer chain in a poor solvent. The spatial distributions of the second-order moment for each of the proteins, obtained from the two sets of hydrophobicity, were compared using the Pearson correlation coefficient; the results reveal that there is a strong correlation between the two data sets for each protein structure when the CHARMM partial atomic charges, |q_i| ≥ 0.3, assigned for polar atoms, are used. The locations at which these distributions vanish and approach a negative value are at approximately 50% of the percentage of solvent accessibility, indicating that there is a transition point from hydrophobic interior to hydrophilic exterior in the proteins. This may suggest that there is a position for the proteins to determine the residues at exposed sites beyond this range.

Translocation of a proteinlike chain through a finite channel

We use the pruned-enriched-Rosenbluth method and the modified orientation-dependent monomer-monomer interaction model to study the translocation of a proteinlike chain through a finite channel. The mean-square radius of gyration per bond <S2>/N and shape factor <delta*> of proteinlike chains with different secondary structures transporting through a finite channel with different channel radii R=1, 2, 3, 4, and 20 are investigated in the translocation. The average Helmholtz free energy per bond A/N and the mechanical force f are also presented. A/N remains unchanged when X(0)<0 and X(0)>1, and decreases monotonously when 0.5<X(0)<0.1. Here X(0)=X/N identical with 2X/L,X is the position of the first monomer, N is chain length, and L is channel length. No free energy barrier is found in our calculation. f is negative and has a plateaulike behavior. The plateau becomes narrow and the value of f increases as R increases. The total energy per bond <U>/N is also calculated in the process of translocation. An energy barrier is shown. The proteinlike chains must cross this energy barrier when they escape from the channel. The position of the maximum of <U>/N depends on the secondary structures and the channel radius. We also discuss the average contact energy per bond <U>c/N, the average alpha-helical energy per bond <U>h/N, and the average beta-sheet energy per bond <U>b/N.