Prokaryotic Expression, Purification and Identification of Human PDE9A Protein

Abstract

Cerebral aggregation of beta amyloid plaques (Aβ) and neurofibrillary tangles is responsible for the onset of Alzheimer’s disease (AD), and PDE9A inhibition rescues Aβ-induced deficits in synaptic plasticity and cognition. This study was aimed to express active PDE9A protein for subsequent inhibitor screening. The PDE9A gene was cloned from human cDNA by real-time polymerase chain reaction, and then the gene sequence and its amino acid sequence were analyzed on Lasergene. An inducible expression vector was constructed by enzyme digestion-seamless cloning and transformed into Escherichia coli BL21 (DE3) for PDE9A expression with isopropyl β-D-1-thiogalactopyranoside (IPTG) as an inducer. The recombinant protein was purified by Ni-NTA affinity chromatography and its activity was determined by a phosphodiesterase assay kit. It was found the open reading frame of PED9A was 1035 bp long, the deduced protein was composed of 345 amino acids, and its predicted isoelectric point was about 4.84. The E. coli vector ST6-PDE9A successfully expressed the recombinant PDE9A protein in the supernatant of bacterial lysate. The optimal culture conditions were that the bacterium ST6-PDE9A was grown first in a lysogeny broth at 37 ºC to an OD₆₀₀ of 0.6-0.8 and then at 16 ºC for 40 h with the addition of 1 M IPTG. Activity test showed PDE9A significantly hydrolyzed the substrate cyclic guanosine monophosphate. In conclusion, we constructed a prokaryotic expression vector and expressed active proteins, laying a solid foundation for screening PDE9 inhibitors.