Purification and Identification of Antimicrobial Protein from the Green Alga <em>Tetraspora</em> Sp. CU2551

Antimicrobial resistance (AMR) is an escalating global health threat, necessitating the discovery of novel antimicrobial agents. Algae-derived proteins and peptides have gained increasing attention for their bioactive potential; however, standardized protocols for investigating antimicrobial peptides (AMPs) in green algae, particularly Tetraspora sp. CU2551, remain limited. This protocol describes a step-by-step workflow for the isolation, purification, and characterization of antimicrobial intact proteins from the green alga Tetraspora sp. CU2551. The procedure integrates optimized protein extraction, chromatographic fractionation, electrophoretic separation, antimicrobial activity screening, and protein identification. Protein extraction conditions are first optimized to reduce background inhibitory effects originating from buffer components. When the identity of the active peptide is unknown, a pull-down assay is applied to assess protein binding across different ion-exchange resins and to guide the selection of an appropriate purification matrix. DEAE-Sepharose ion-exchange chromatography is a suitable method for enriching antimicrobial protein fractions. All fractions are systematically evaluated for antimicrobial activity and analyzed by SDS-PAGE. The protein band corresponding to the highest antimicrobial activity, along with a distinct electrophoretic profile, is excised and subjected to LC-MS/MALDI-TOF analysis for protein identification. The workflow is further complemented by in silico analyses to predict antimicrobial peptide-related properties using publicly available bioinformatic tools. This protocol provides a versatile framework for antimicrobial protein discovery and can be readily adapted to other algal species and related biotechnological applications.