Promiscuous protein biotinylation by Escherichia coli biotin protein ligase

Abstract

Biotin protein ligases (BPLs) are enzymes of extraordinary specificity. BirA, the BPL of Escherichia coli biotinylates only a single cellular protein. We report a mutant BirA that attaches biotin to a large number of cellular proteins in vivo and to bovine serum albumin, chloramphenicol acetyltransferase, immunoglobin heavy and light chains, and RNAse A in vitro. The mutant BirA also self biotinylates in vivo and in vitro. The wild type BirA protein is much less active in these reactions. The biotinylation reaction is proximitydependent in that a greater extent of biotinylation was seen when the mutant ligase was coupled to the acceptor proteins than when the acceptors were free in solution. This approach may permit facile detection and recovery of interacting proteins by existing avidin/streptavidin technology.Keywords: biotin protein ligase; protein modification; biotinylation; acyl adenylate; BirA Biotinylation of proteins has routinely been done by chemical means, usually by modification of protein amino groups with biotin-N-hydroxysuccinimide or similar acylating agents. In contrast, enzymatic biotinylation has been limited to the few proteins that normally carry this modification, which are largely biotin-dependent carboxylases and decarboxylases of central metabolism (Chapman-Smith and Cronan Jr. 1999). We supposed that if enzymatic biotinylation could be made less specific, it might provide a means to detect weak (i.e., having dissociation constants >10 −7 M) protein-protein interactions. In this scenario the biotinylating enzyme physically coupled to one of the interacting proteins (the target protein) would be used to biotinylate and thereby tag proteins that interact with the target protein. The biotinylation reaction should tag only those protein molecules that are close in space to the target protein. That is, unlike chemical acylation, enzymatic biotinylation should be proximity-dependent. The specific and extremely tight binding of biotin (K D 10 −13 to 10 −15 M) to streptavidin and avidin would then allow very sensitive detection of biotinylated proteins by a wide variety of robust protocols and low affinity forms of streptavidin and avidin allow efficient purification of biotinylated proteins under mild conditions. However, the biotin protein ligases (BPLs) catalyzing protein biotinylation have exceptional specificities for their protein substrates and thus are not general protein modification enzymes. For example, in vivo, BirA, the BPL of Escherichia coli, biotinylates only a single protein, the BCCP (AccB) subunit of acetyl-CoA carboxylase and other organisms contain less than five biotinylated protein species, indicating these BPLs are similarly specific (McAllister and Coon 1966;Samols et al. 1988;. Therefore, in order to use a BPL as a general biotinylating enzyme, this extraordinary specificity must somehow be overcome. A possible route to this end is based upon the mechanism of the BPL reaction, which proceeds in two steps:1. Biotin + ATP Bio-5Ј-AMP + PPi 2. Bio-5Ј-AMP + apo-Prot...

Altered Regulation of Escherichia coli Biotin Biosynthesis in BirA Superrepressor Mutant Strains

“…All of the mutant alleles tested were recessive to the wild-type allele, indicating that they were loss-of-function mutations (6). Subsequent work on several of these mutant strains showed that the defects in biotin utilization reflected compromised ligase activity due to decreased affinities for biotin and/or biotinoyl-adenylate (13,24). We report isolation of the first gain-of-function (genetically dominant) birA superrepressor alleles.…”

Genetically engineered avidins and streptavidins

“…However, the determinants of the specificity of BPL-mediated biotinylation are only partially known [132]. One interesting finding was recently made by Choi-Rhee and coworkers [133], who observed less specific biotinylation occurring due to a mutation in the E. coli biotin holoenzyme synthetase/ bio receptor BirA. A mutagenesis of BirA leading to a new sequence specificity could thus be obtained, offering an efficient tool for life science.…”

Identification and characterization of acetyl-CoA carboxylase gene cluster in Streptomyces toxytricini

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