Rigid linker peptides improve the stability and anti-inflammation effect of human serum albumin and α-melanocyte-stimulating hormone fusion proteins

The anti-inflammatory effect of alpha-melanocyte-stimulating hormone (alpha-MSH) in the central nervous system (CNS) has been reported for 40 years. However, the short half-life of alpha-MSH limits its clinical applications. The previous study has shown that a fusion protein comprising protein transduction domain (PTD), human serum albumin (HSA), and alpha-MSH extends the half-life of alpha-MSH, but its anti-inflammatory effect is not satisfactory. In this study, optimization of the structures of fusion proteins was attempted by changing the linker peptide between HSA and alpha-MSH. The optimization resulted in the improvement of various important characteristics, especially the stability and anti-inflammatory bioactivity, which are important features in protein medicines. Compared to the original linker peptide L0, the 5-amino-acid rigid linker peptide L6 (PAPAP) is the best option for further investigation due to its higher expression (increased by 6.27%), improved purification recovery (increased by 60.8%), excellent thermal stability (Tm = 83.5 degrees C) and better inhibition in NF-kappa B expression (increased by 81.5%). From this study, the significance of the design of linker peptides in the study of structure-activity relationship of fusion proteins was proved.