科研之友
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摘要
The silica forming repeat R5 of sil1 from Cylindrotheca fusiformis was the blueprint for the design of P5S3, a 50-residue peptide which can be produced in large amounts by recombinant bacterial expression. It contains 5 protein kinase A target sites and is highly cationic due to 10 lysine and 10 arginine residues. In the presence of supersaturated orthosilicic acid P5S3 enhances silica-formation whereas it retards the dissolution of amorphous silica (SiO2) at globally undersaturated concentrations. The secondary structure of P5S3 during these 2 processes was studied by circular dichroism (CD) spectroscopy, complemented by nuclear magnetic resonance (NMR) spectroscopy of the peptide in the absence of silicate. The NMR studies of dual-labeled (C-13, N-15) P5S3 revealed a disordered structure at pH 2.8 and 4.5. Within the pH range of 4.5-9.5 in the absence of silicic acid, the CD data showed a disordered structure with the suggestion of some polyproline II character. Upon silicic acid polymerization and during dissolution of preformed silica, the CD spectrum of P5S3 indicated partial transition into an -helical conformation which was transient during silica-dissolution. The secondary structural changes observed for P5S3 correlate with the presence of oligomeric/polymeric silicic acid, presumably due to P5S3-silica interactions. These P5S3-silica interactions appear, at least in part, ionic in nature since negatively charged dodecylsulfate caused similar perturbations to the P5S3 CD spectrum as observed with silica, while uncharged beta-D-dodecyl maltoside did not affect the CD spectrum of P5S3. Thus, with an associated increase in -helical character, P5S3 influences both the condensation of silicic acid into silica and its decondensation back to silicic acid.
- 出版日期2017-11
