# Exploring Metalloprotease from _Dunaliella_ sp.: Production, Regulation, and Structural Insight
## 1 Introduction
Green algae constitute an evolutionary phylum between cyanobacteria and plants, so it is straightforward that FtsH homologs in algae are more numerous than in cyanobacteria and fewer than in plants. For example, _Chlamydomonas reinhardtii_ possesses three FtsH and six FtsH homologs [22; 23; 24]. FtsHi denotes a subgroup of FtsH proteins with deactivated proteolytic activity. Among these homologs, CrFtsH1 and CrFtsH2 play crucial roles in overseeing the quality of thylakoid membrane proteins, including the repair of PSII and the degradation of cytochrome b\({}_{6}\)[22; 25; 26]. The rich biodiversity of marine ecosystems serves as a natural reservoir for identifying biocatalysts with significant industrial and pharmaceutical potential [27; 28; 29; 30]. _Dunaliella_ (Chlorophyta, Chlorophyceae), a halotolerant unicellular green alga, stands out as a highly versatile eukaryotic organism because of its ability to withstand abiotic stress, making it a compelling model system investigating stress physiology [31]. Typically, _Dunaliella_ species exhibit an ovoid shape, are flagellated, and lack a rigid polysaccharide wall, although they are enveloped by a mucilaginous glycoprotein coat known as a glycocallyx [32]. _Dunaliella salina_ thrives in hypersaline settings like salt lakes and salt evaporation ponds, imparting a distinct pink hue to these environments. Its response to high salinity involves the biosynthesis of abundant glycerol to counter osmotic pressure, along with notable concentrations of \(\beta\)-carotene [33]. Renowned for its rich nutrient profile, particularly its high \(\beta\)-carotene content [34], _Dunaliella_ strains serve as a cornerstone in the production of dietary supplements [35]. Their antioxidant properties also find applications in cosmetics and skincare. _Dunaliella_ species also demonstrate potential in environmental remediation by absorbing heavy metals and pollutants from water. Moreover, _Dunaliella_ is emerging as a candidate for biofuel production, owing to its lipid accumulation properties [36]. To date, research on _Dunaliella_ species has primarily focused on their bioactive compounds, such as astaxanthin, \(\beta\)-carotene, and glycerol. However, proteins have received relatively little attention, despite constituting up to 57% of the biomass in some cases. Thisstudy aims to optimize various culture parameters of _Dunaliella_ sp., such as salinity, to maximize protein biosynthesis. Preliminary studies indicate that salt stress can enhance proteolytic activity. Notably, the role of the FtsH2 metalloproteinase has been linked to the organism's defense against salt stress. Metalloproteases are crucial for maintaining cellular homeostasis during stress by facilitating protein degradation and recycling. Specifically, FtsH2 has been found to be produced at elevated levels under salt stress conditions, where damaged proteins may accumulate following oxidative stress and other factors. Most existing research tends to focus on broader stress responses or different metabolic pathways, leaving a gap in our understanding of the specific roles and regulatory mechanisms of FtsH2 under stressful conditions. Thus, studying FtsH2 is of particular interest, as it may provide valuable insights into how _Dunaliella_ species manage protein quality control in extreme environments.