Impact of glycerol feeding profiles on STEAP1 biosynthesis by Komagataella pastoris using a methanol-inducible promoter

Specific Six-Transmembrane Epithelial Antigen of the Prostate 1 Capture with Gellan Gum Microspheres: Design, Optimization and Integration

This work demonstrates the potential of calcium- and nickel-crosslinked Gellan Gum (GG) microspheres to capture the Six-Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1) directly from complex Komagataella pastoris mini-bioreactor lysates in a batch method. Calcium-crosslinked microspheres were applied in an ionic exchange strategy, by manipulation of pH and ionic strength, whereas nickel-crosslinked microspheres were applied in an affinity strategy, mirroring a standard immobilized metal affinity chromatography. Both formulations presented small diameters, with appreciable crosslinker content, but calcium-crosslinked microspheres were far smoother. The most promising results were obtained for the ionic strategy, wherein calcium-crosslinked GG microspheres were able to completely bind 0.1% (v/v) DM solubilized STEAP1 in lysate samples (~7 mg/mL). The target protein was eluted in a complexed state at pH 11 with 500 mM NaCl in 10 mM Tris buffer, in a single step with minimal losses. Coupling the batch clarified sample with a co-immunoprecipitation polishing step yields a sample of monomeric STEAP1 with a high degree of purity. For the first time, we demonstrate the potential of a gellan batch method to function as a clarification and primary capture method towards STEAP1, a membrane protein, simplifying and reducing the costs of standard purification workflows.

Mini-Bioreactor Platform for Membrane Protein Production in Komagataella pastoris

Membrane proteins (MPs) play vital roles across various cellular functions, biological processes, physiological signaling pathways, and human-related disorders. Considering the clinical relevance of MPs and their application as therapeutic targets, it is crucial to explore highly effective production platforms and purification approaches to ultimately obtain a high-resolution structure of the target. Therefore, it would be possible to gather detailed knowledge on their mechanism of action which will be the basis for the rational design of novel and stronger drugs. Unfortunately, when compared to their soluble counterparts, 3D structures of MPs are really scarce (<2%), mainly due to poorly natural abundance, challenges associated with protein solubility and stability, and difficulties in producing bioactive and properly structural folded targets. These drawbacks could significantly impair the use of MPs as therapeutic targeting and demand efforts to develop tailor-made strategies for their appropriate handling. Therefore, this chapter is focused on describing a detailed and high-throughput procedure for the biosynthesis of MPs using Komagataella pastoris cell cultures as expression system in a mini-bioreactor platform. Additionally, insights on a purification strategy that combines immobilized-metal affinity and ion-exchange chromatography are described to further obtain the target protein with a significant degree of purity.

Enhanced Stability of Detergent-Free Human Native STEAP1 Protein from Neoplastic Prostate Cancer Cells upon an Innovative Isolation Procedure

BACKGROUND

The STEAP1 is a cell-surface antigen over-expressed in prostate cancer, which contributes to tumor progression and aggressiveness. However, the molecular mechanisms underlying STEAP1 and its structural determinants remain elusive.

METHODS

The fraction capacity of Butyl- and Octyl-Sepharose matrices on LNCaP lysates was evaluated by manipulating the ionic strength of binding and elution phases, followed by a Co-Immunoprecipitation (Co-IP) polishing. Several potential stabilizing additives were assessed, and the melting temperature (Tm) values ranked the best/worst compounds. The secondary structure of STEAP1 was identified by circular dichroism.

RESULTS

The STEAP1 was not fully captured with 1.375 M (Butyl), in contrast with interfering heterologous proteins, which were strongly retained and mostly eluted with water. This single step demonstrated higher selectivity of Butyl-Sepharose for host impurities removal from injected crude samples. Co-IP allowed recovering a purified fraction of STEAP1 and contributed to unveil potential physiologically interacting counterparts with the target. A Tm of ~55 °C was determined, confirming STEAP1 stability in the purification buffer. A predominant α-helical structure was identified, ensuring the protein's structural stability.

CONCLUSIONS

A method for successfully isolating human STEAP1 from LNCaP cells was provided, avoiding the use of detergents to achieve stability, even outside a membrane-mimicking environment.