The project “Development of recombinant phenylalanine‑free protein GSP105 for PKU diet management” brought together metaX Institut für Diätetik GmbH and Fraunhofer Institute for Molecular Biology and Applied Ecology IME to create an industrially viable, Phe‑free protein for patients with phenylketonuria (PKU). The collaboration focused on engineering a robust production platform, scaling fermentation, optimizing downstream purification, and validating the product in a preclinical mouse model.

Technical Results
Expression system selection was guided by a comparative study of Bacillus subtilis strains and the Gram‑negative host Pseudomonas fluorescens. The latter proved the most efficient and cost‑effective, delivering high expression levels while maintaining protein quality. Fermentation was scaled to a 100 L pilot plant and further optimized to a 140 L fed‑batch process that demonstrated reproducible yields and process stability suitable for industrial deployment.
Downstream processing employed immobilized metal ion affinity chromatography (IMAC). A 20 L column processed 40 L of GSP‑containing extract, recovering 190 g of purified GSP105 per run. This represents a significant throughput for a single purification cycle and indicates a low cost of goods when scaled. The purification strategy was chosen for its high selectivity, minimal buffer consumption, and compatibility with food‑grade standards.
Preclinical evaluation used a PKU mouse model to assess the therapeutic potential of GSP105. The study confirmed that the recombinant protein is well tolerated, provides essential amino acids without phenylalanine, and improves metabolic parameters in the animal model. Statistical analysis of the feeding trial demonstrated significant improvements in plasma phenylalanine levels compared to control groups, supporting the protein’s efficacy as a dietary supplement for PKU patients.
Regulatory readiness was addressed through the preparation of a European patent application (EP) and an international PCT filing. The EP patent was granted after 26 months, securing intellectual property protection for the production process and the protein product. The project also laid the groundwork for a Novel Food and Medical Food approval application, positioning GSP105 for market entry.

Collaboration
metaX led the technical aspects of product development, including the design of the preclinical study, chemical analysis, and the preparation of regulatory submissions. Fraunhofer IME focused on process engineering, establishing the fermentation and purification protocols, and performing quality control analyses. The partnership was organized into eight work packages, with metaX responsible for AP1, AP5, and AP8, Fraunhofer for AP2 and AP3, and joint effort on AP4, AP6, and AP7.
Regular project meetings and data reviews ensured alignment across the partners. The collaboration extended to Prof. Dr. Beat Thöny from the University Children’s Hospital Zurich, who conducted the PKU mouse feeding study on behalf of metaX. This external expertise reinforced the scientific validity of the preclinical results.
Through coordinated efforts, the consortium achieved a scalable production platform, validated product efficacy, and secured intellectual property, setting the stage for regulatory approval and commercial launch of a novel, Phe‑free protein for PKU diet management.