Expression, purification, and characterization of authentic mouse prolactin obtained in Escherichia coli periplasmic space

Prolactin (PRL) is a pleiotropic hormone produced by lactotroph cells of the anterior pituitary gland and is mainly related to lactation control and reproduction. Recombinant mouse prolactin (r-mPRL), never obtained in its authentic form, can be very useful for research and tests in animal models, in which human prolactin (hPRL) is usually employed in a heterologous mode. Synthesis of r-mPRL was carried out here via secretion in Escherichia coli periplasmic space using a plasmid containing mPRL cDNA joined to the DsbA signal peptide sequence under the control of a constitutive major leftward promoter of the bacteriophage λ (λ_PL). Fermentation in a pilot bioreactor was carried out at 30°C, with 6 H of induction at 37°C, reaching an optical density of 23 A₆₀₀ units, a specific yield of 0.06-0.1 μg mPRL/(mL A₆₀₀), and a concentration of up to 2.2 μg/mL. Even with such a low yield and a poor mass fraction, r-mPRL was purified via a three-step laboratory process based on hydrophobic chromatography, reversed-phase high-performance liquid chromatography, and high-performance size-exclusion chromatography (HPSEC). The purified hormone was then characterized using SDS-PAGE, Western blotting, and HPSEC and showed, by Nb2 rat lymphoma cell proliferation assay, a bioactivity of 39.5 IU/mg, determined against the International Standard of recombinant hPRL [World Health Organization (WHO)-97/714].