Exploring Metalloprotease from Dunaliella sp.: Production, Regulation, and Structural Insight

A green microalgal strain, identified as Dunaliella sp., was isolated from the Tunisian southern region. The enhancement of its protein and protease production was performed through culture condition optimization using the response surface methodology. The optimal conditions for protein and protease production were found to be, respectively, (i) NaCl concentrations of 135 and 45.55 g/L, (ii) NaHCO3 concentrations of 0.5 and 1.5 g/L, (iii) temperature of 28 °C for both, and (iv) light intensities of 400 and 100 µmol photons/m2/s. The optimization led to an increase in microalgae protein content from 11.98% ± 0.26 to 18.39% ± 0.10 and microalgae proteolytic activity from 7.36 ± 0.74 U/mg to 12.54 ± 0.86 U/mg. Specific focus was attributed to ATP-dependent metalloprotease, namely, FtsH2, which is involved in numerous cellular processes including cell division, cell differentiation, signal transduction, and stress response. Differential expression of the FtsH2 gene under various stress conditions showed that this expression was upregulated in response to salt stress, gibberellic acid, and Indole-3-butyric acid. A 3D modeling demonstrated two possible arrangements where the ATPase ring shows either a perfect six-fold symmetry with an open circular entrance covering the crucial pore residues, or a translocated model triggered by substrate binding inward movement of the aromatic pore residues.