Microplate-based method to screen inhibitors of isozymes of cyclic nucleotide phosphodiesterase fused to SUMO

Comparison of the Full-Length and 152~528 Truncate of Human Cyclic Nucleotide Phosphodiesterase 4B2 for the Characterization of Inhibitors

AIM AND OBJECTIVE

Human full-length cyclic nucleotide phosphodiesterase isozyme 4B2 (hPDE4B2) as the target for screening and characterizing inhibitors suffers from low activity yield and the coexistence of two conformational states bearing different affinities for (R)-rolipram. Hence, the 152~528 truncate of hPDE4B2 existing only in the low-affinity conformation state for (R)-rolipram was compared against the full-length hPDE4B2 to characterize inhibitors.

MATERIALS AND METHODS

With 6His-SUMO tag at the N-terminus, both the full-length hPDE 4B2 (SF-hPDE4B2) and the 152~528 truncate (ST-hPDE4B2) were expressed in Escherichia coli cells, purified through Ni-NTA column and compared for the characterization of inhibitors. The inhibition constants (Ki) of some synthesized rolipram analogues against both targets were determined with 96-well microplate through the coupled action of monophosphatase on AMP and spectrophotometric assay of phosphate with malachite green.

RESULTS

After affinity purification with Ni2+-NTA column, ST-hPDE4B2 showed about 30-fold higher specific activity and 100-fold higher activity yield than SF-hPDE4B2; Ki of (R)-rolipram on ST-hPDE4B2 was consistent with that on the low-affinity state of the untagged full-length hPDE4B2 expressed in insect cells. Of some representative rolipram analogues as inhibitors, a dual-logarithm model quantitatively described their monotonic association, and Ki from 0.010 mM to 8.5 mM against SF-hPDE4B2 was predicted from Ki against ST-hPDE4B2, supporting the discovery of consistent hits by the use of both targets with a pair of properly-set cutoffs.

CONCLUSION

ST-hPDE4B2 with much higher activity yield may be a favorable alternative target to characterize/screen rolipram analogues as hPDE4B inhibitors in high-throughput mode.

Prokaryotic expression and action mechanism of antimicrobial LsGRP1C recombinant protein containing a fusion partner of small ubiquitin-like modifier

Antimicrobial peptides (AMPs) are peptides exhibiting broad-spectrum antimicrobial activities and considered as potential therapeutic agents. LsGRP1^C, a novel AMP derived from defense-related LsGRP1 protein of Lilium, was proven to inhibit kinds of bacteria and fungi via alteration of microbial membrane permeability and induction of fungal programmed cell death-like phenomena by in vitro assays using synthetic LsGRP1^C. In this study, the prokaryotic production of LsGRP1^C recombinant protein containing an N-terminal fusion partner of the yeast small ubiquitin-like modifier (SUMO) was achieved by using optimized Escherichia coli host and purification buffer system, which lead to a high yield of soluble SUMO-LsGRP1^C fusion protein. In vitro assay revealed that E. coli-expressed SUMO-LsGRP1^C exhibited even better antifungal activity as compared to synthetic LsGRP1^C. Meanwhile, the ability of SUMO-LsGRP1^C in conducting fungal membrane permeabilization and programmed cell death was verified by SYTOX Green staining and 4',6-diamidino-2-phenylindole staining/terminal deoxynucleotidyl transferase dUTP nick-end labeling assays, respectively, indicating that E. coli-expressed SUMO-LsGRP1^C shares identical modes of action with synthetic LsGRP1^C. Herein, this E. coli expression system enables the effective and convenient production of antimicrobial LsGRP1^C in a form of SUMO-fused recombinant protein.