The circadian clock times cellular processes to the day/night cycle via a Transcription-Translation negative Feedback Loop (TTFL). However, a mechanistic understanding of the negative arm in both the timing of the TTFL and its control of output is lacking. We posited that the formation of negative-arm protein complexes was fundamental to clock regulation stemming from the negative arm. Using a modified peptide microarray approach termed Linear motif discovery using rational design (LOCATE), we characterized the interaction of the disordered negative-arm clock protein FREQUENCY to its partner protein FREQUENCY-Interacting RNA helicase. LOCATE identified a specific Short Linear Motif (SLiM) and interaction hotspot as well as positively charged islands that mediate electrostatic interactions, suggesting a model where negative arm proteins form a fuzzy complex essential for clock timing and robustness. Further analysis revealed that the positively charged islands were an evolutionarily conserved feature in higher eukaryotes and contributed to proper clock function.
BACKGROUND: In this study, we have demonstrated the design, screening and selection of peptide ligands for the affinity capture of human growth hormone (hGH) from yeast cell cultures.
RESULTS:Ligand design was carried out using multiple approaches based on primary sequence and structures of natural binding partners of hGH. Screening of potential affinity peptides was conducted using high throughput microarray platforms followed by assessment of in-solution binding to hGH using fluorescence polarization. Peptide leads were subsequently immobilized on chromatographic resins and the binding and desorption behavior was examined using batch adsorption studies. A lead candidate was examined in further details in column chromatography studies which indicated that while high purity was attained, further refinement was necessary for improved product recovery. Histidine scanning was employed to successfully improve the recovery of hGH from cell culture fluid while still maintaining high purity. Finally, proof-of-concept was demonstrated in the column format using complex feed stock where a product purity of 95% was attained at 80% yield. CONCLUSION: The approaches presented here can be translated to other biologics of interest for the rapid development of affinity based purification processes.
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