Development of an IP-Free Biotechnology Platform for Constitutive Production of HPV16 L1 Capsid Protein Using the Pichia pastoris PGK1 Promoter

Figure 4

HPV VLPs self-assembly within the P. pastoris cells. (a and b) Electrodense structures (VLPs) with estimated diameters of 55 nm were observed near the endoplasmic reticulum (ER) membranes of P. pastoris clones expressing L1 protein under regulation of PGK1 promoter. (c–e) VLPs were visualized both near and inside the autophagic bodies (AB) and were either free from or in contact with the AB membranes. (f) Circumstantially, the VLPs were seen to be transiting in cytoplasm. (g) Close-up of electrodense structures with an estimated size of 20 nm and cluster on ER membranes, which were identified as ribosomes. (h) Similar particles with 55 nm were not observed in the P. pastoris cells that were transformed with parental vectors, either in the cytosol or inside AB. (Bar = 200 nm in (a); 80 nm in (b)–(d), (f), and (h); 100 nm in (e); 40 nm in (g)).

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