Elucidation of a new biological function of an old protein: unique structure of the cobra serum albumin controls its specific toxin binding activity

作者：Wang X; Buck F; Havsteen B^*

来源：International Journal of Biochemistry & Cell Biology, 1998, 30(2): 225-233.

DOI：10.1016/S1357-2725(97)00113-1

• mutagenesis
• proteolysis
• conformation
• cobra serum albumin
• disulfide linkage
• toxin binding

Although few proteins have been studied as thoroughly as serum albumin, a new biological property of this evolutionary ancient protein was recently discovered: The ability of cobra serum albumin (CSA) to specifically sequester lethal endogenous toxins. A study of the structural basis of this property is reported in this contribution. Two independent approaches were used to alter the structure of the CSA at defined positions: Directed mutagenesis and limited proteolysis. The conserved pattern of the disulfide linkages in the primary structure of the serum albumins showed in the case of the cobra snake (Naja naja kaouthia) an anomaly at C-11 and C-502, which suggested the existence of a unique spatial structure in this protein. The two cysteine residues were singly replaced with the consensus residue, i.e. C-11-->F and C-502-->T. The former substitution increased the specific neurotoxin binding capacity of the CSA by the factor 1.7 +/- 0.2, whereas the latter replacement reduced it to (25 +/- 2)%. The limited proteolysis yielded the large tryptic peptides T60, T40, T30 and Tig, which after isolation by PAGE followed by HPLC had retained a strong toxin affinity. The location of these peptides in the amino-acid sequence was identified by Edman degradation and suggested the order of their release. On the basis of these data, a model of the unfolding and of the activity changes of the CSA caused by the structural perturbations was composed and the kinetic parameters associated with the process were evaluated. The results support the hypothesis of the existence of a structure of multiple homologous domains with a disulfide linkage between C-11 and C-502 in, the native CSA that joins the chain ends to form a dense conformation.

• 出版日期1998-2