Thermostable properties of the equine infectious anemia virus nucleocapsid protein NCp11

Retroviral nucleocapsid (NC) proteins are multifunctional nucleic acid binding proteins, playing critical roles in essentially every step of the viral replication cycle. As a small, basic protein, NC contains one or two highly conserved zinc-finger domains, each having an invariant CCHC motif, flanked by basic residues. In this study, we report for the first time, to our knowledge, the thermostable property of equine infectious anemia virus (EIAV) NCp11. About 43% of purified NCp11 remained soluble after incubation at 100 °C for 60 min, and heat-treated NCp11 maintained its abilities to bind to the E. coli RNA and the EIAV packaging signal sequence. At a very high degree of sequence occupancy, NCp11 inhibited first-strand cDNA synthesis catalyzed by either a commercial or the purified EIAV reverse transcriptase, and heat-treated NCp11 still inhibited the first-strand cDNA synthesis. We also found that protein concentrations, at a range from 0.1 to 0.9 μg/μl, have not affected the NCp11 thermostability significantly. However, NCp11 at acidic pH was more thermostable. Our findings highlight a new feature of the NC protein. Detailed understanding of NC's properties and functions will facilitate the development of effective and rational therapeutic strategies against retroviruses.