Phe labeled NS3 helicase 3.3.2 DENV4 NS3 helicase expression 3.3.2.1 NS3 helicase protein expression protocol 3.3.3 Purification of DENV4 NS3 helicase 3.3.3.1 NS3 helicase purification protocol 3.4 Results and Discussion 3.4.1 Expression and purification of NS3 helicase 3.4.2 NMR spectroscopy of DENV4 NS3 helicase 3.4.2.1 Resonance assignment process 3.4.2.2 1-13 C-Leu, 1-13 C-Ala selective labeling in a 2 H, 15 N background 3.4.3. Preliminary PRE studies 3.4.4 Design, high-level expression and purification of fragments of DENV 4 NS3 helicase 3.4.4.1 Design of a truncated β hairpin in subdomain 2 3.4.4.2 High-level expression and purification of the designed fragments of DENV4 NS3 helicase Conclusion 4. Conclusion and future perspectives