Investigation of the structure and stability of the HIV-1 vaccine candidate recombinant Tat protein

Human immunodeficiency virus (HIV) remains one of the major global public health issues and challenges. The HIV-1 trans-activator of transcription Tat protein is one of the most promising AIDS vaccine candidates and plays central roles in the virus’s life cycle and pathogenesis. The maintenance of the structural integrity of a therapeutic recombinant protein is very essential for its efficacy in relation to its physiological and pharmacological activity. These factors are directly affected with the protein correct folding. This study aimed to investigate the structural properties and stability of the HIV-1 vaccine candidate recombinant Tat protein using the spectroscopic methods. After the recombinant plasmid (pET28a-tat) preparation and transformation, its expression was optimized in the prokaryotic host cells (E.coli-Bl21 (DE3)). The His6-tagged recombinant protein was then produced in a large scale and purified using a Ni-NTA resin. To eliminate the interference effect of imidazole, the pure recombinant Tat protein was dialyzed in different buffers (according to the desired experiment) and its structure and stability were investigated using the spectroscopic methods. The results showed that the HIV-1 Tat protein maintains its structural integrity following the incubation in some stress conditions including high temperatures up to 50 °C, but it loses its integrity at higher temperatures. The compounds such as ZnCl2, NaCl and sucrose help to maintain the vaccine’s structure and increase its stability. The recombinant protein is somewhat sensitive to acidic or alkaline pHs and also chemical treatments, and in extreme conditions loses its structure. The results of circular dichroism analysis showed that the protein has no significant ordered structure. These results were also confirmed by those obtained from theoretical studies.