Structural and physicochemical characteristics of novel basic proteins isolated from duck egg white.

Novel basic proteins, duck basic protein small 1 (dBPS(1)) and 2 (dBPS(2)), 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 dBPS(1) showed 45% identity with dBPS(2). The amino acid sequence of dBPS(2) was the same as cygnin, a small protein from black swan, and strongly homologous with meleagrin from turkey and chicken. Phylogenic relationships implied that dBPS(1) and dBPS(2) share a common ancestry with cygnin and meleagrin. Based on MALDI-TOF mass spectra, the molecular masses of dBPS(1) and dBPS(2) were 4,373, and the 4,486 Da. pI of dBPS(1) and dBPS(2) elucidated by isoelectric focusing were 9.35 and 9.44. FT-IR spectra classified these proteins as (beta) proteins. Both dBPS(1) and dBPS(2), possessed high heat stability, Td 101.2 and 98.3 degrees C. Indirect ELISA results showed that the dBPS(1)/dBPS(2)-related proteins were distributed in the oviduct and gallbladder.