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The structure of the complex between avidin and the dye, 2‐(4'‐hydroxyazobenzene) benzoic acid (HABA)
Author(s) -
Livnah Oded,
Bayer Edward A.,
Wilchek Meir,
Sussman Joel L.
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)80986-5
Subject(s) - avidin , streptavidin , chemistry , biotin , benzoic acid , stereochemistry , ring (chemistry) , moiety , crystallography , biochemistry , organic chemistry
The crystal structure of the complex formed between the egg‐white biotin‐binding protein, avidin, and the dye, 2‐(4'‐hydroxyazobenzene) benzoic acid (HABA), was determined to a resolution of 2.5 A. The interaction of avidin with the benzoate ring of HABA is essentially identical to that of the complex formed between HABA and streptavidin (the bacterial analogue of the egg‐white protein). This interaction emulates the definitive high‐affinity interaction of both proteins with the ureido moiety of biotin. The major difference between the avidin‐ and streptavidin‐HABA complexes lies in their interaction with the hydroxyphenyl ring of the dye molecule; in avidin, two adjacent amino acid residues (Phe 72 and Ser 73 ), which are not present in streptavidin, form additional interactions with this ring. These are suggested to account for the higher affinity of avidin for HABA. The characteristic red shift, which accompanies the interaction of both proteins with the dye, was traced to a proposed charge‐transfer complex formed between the hydroxyphenyl ring of HABA and the indole ring of Trp 70 in avidin (Trp 79 in streptavidin). Comparison of binding site residues of two such similar proteins versus their markedly different affinities for two such different substrates should eventually contribute to a better design of biomimetic reagents and drugs.