A Competitive High-Throughput Screening Platform for Designing Polylactic Acid-Specific Binding Peptides

Among biobased polymers, polylactic acid (PLA) is recognized as one of the most promising bioplastics to replace petrochemical-based polymers. PLA is typically blended with other polymers such as polypropylene (PP) for improved melt processability, thermal stability, and stiffness. A technical challenge in recycling of PLA/PP blends is the sorting/separation of PLA from PP. Material binding peptides (MBPs) can bind to various materials. Engineered MBPs that can bind in a material-specific manner have a high potential for material-specific detection or enhanced degradation of PLA in mixed PLA/PP plastics. To obtain a material-specific MBP for PLA binding (termed PLA(bodies)), protein engineering of MBP Cg-Def for improved PLA binding specificity is reported in this work. In detail, a 96-well microtiter plate based high-throughput screening system for PLA specific binding (PLABS) was developed and validated in a protein engineering (KnowVolution) campaign. Finally, the Cg-Def variant V2 (Cg-Def S19K/K10L/N13H) with a 2.3-fold improved PLA binding specificity compared to PP was obtained. Contact angle and surface plasmon resonance measurements confirmed improved material-specific binding of V2 to PLA (1.30-fold improved PLA surface coverage). The established PLABS screening platform represents a general methodology for designing PLA(bodies) for applications in detection, sorting, and material-specific degradation of PLA in mixed plastics.