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Functional Analysis of Prokaryotic SELB proteins
Author(s) -
Thanbichler Martin,
Böck August
Publication year - 2001
Publication title -
biofactors
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.204
H-Index - 94
eISSN - 1872-8081
pISSN - 0951-6433
DOI - 10.1002/biof.5520140108
Subject(s) - elongation factor , guanosine , gtp' , transfer rna , biochemistry , ribosomal protein , amino acid , biology , ribosome , nucleotide , guanosine triphosphate , ribosomal rna , protein tertiary structure , selenocysteine , rna , chemistry , enzyme , cysteine , gene
Since the discovery of selenocysteine as the 21st amino acid considerable progress has been made in elucidating the system responsible for its insertion into proteins. Elongation factor SELB, whose amino‐terminal part shows homology to EF‐Tu, was found to be the key component mediating delivery of selenocysteyl‐tRNA Sec to the ribosomal A site. It exhibits a distinct tertiary structure comprising binding sites for guanosine nucleotides, the cognate tRNA, an mRNA secondary structure (SECIS element) and presumably ribosomal components. The kinetics of interaction of SELB with its ligands have been studied in detail. GDP was found to bind with about 20‐fold lower affinity than GTP and to be in rapid exchange, which obviates the need for a guanosine nucleotide exchange factor. The affinity of SELB for the SECIS element is in the range of 1 nM and further increases upon binding of selenocysteyl‐tRNA Sec to the protein. This supports the model that SELB forms a tight quaternary complex on the SECIS element which is loosened after insertion of the tRNA into the ribosomal A site and the concomitant hydrolysis of GTP.