There has been an idea to load a pharmaceutical agent in a barrel structure of a lipocalin-type prostaglandin D synthase, and to seal the pharmaceutical agent in the barrel structure by introducing a disulfide bond between H2-helix and E-F loop.

However, in some cases the pharmaceutical agent is released through a gap in the vicinity of the open mouth of the barrel structure.

The present capsule protein has substitution of alanine residue for a cysteine residue of the active center of the human lipocalin-type prostaglandin D synthetase. The protein further has substitution of barrier amino acid residue(s) for at least one amino acids of D strand. The barrier amino acids in the D-strand, located in the vicinity of the open mouth of its barrel structure suppresses the leak of the pharmaceutical agent.

The present disclosure relates to the pharmaceutical field. Specifically, the present disclosure relates to a novel Lipocalin-type prostaglandin D synthase (L-PGDS) mutant (RA L-PGDS) as well as its use in the treatment of amyloid-related diseases.