Structural and Physicochemical Characteristics of Novel Basic Proteins Isolated from Duck Egg White

Novel basic proteins, duck basic protein small 1 (dBPS₁) and 2 (dBPS₂), were isolated from duck egg white by cation-exchange and gel filtration chromatography. Protein sequence analyses indicated that they possessed 39 amino acid residues with three disulfide bonds. The amino acid sequence of dBPS₁ showed 45% identity with dBPS₂. The amino acid sequence of dBPS₂ was the same as cygnin, a small protein from black swan, and strongly homologous with meleagrin from turkey and chicken. Phylogenic relationships implied that dBPS₁ and dBPS₂ share a common ancestry with cygnin and meleagrin. Based on MALDI-TOF mass spectra, the molecular masses of dBPS₁ and dBPS₂ were 4,373, and the 4,486 Da. pI of dBPS₁ and dBPS₂ elucidated by isoelectric focusing were 9.35 and 9.44. FT-IR spectra classified these proteins as (β) proteins. Both dBPS₁ and dBPS₂, possessed high heat stability, Td 101.2 and 98.3 °C. Indirect ELISA results showed that the dBPS₁/dBPS₂-related proteins were distributed in the oviduct and gallbladder.