Methionine surrogates

Fig. 6 Left Cell-selective BONCAT method. Cells that cany the mmant MetRS (NLL-MRS) can be labeled with the methionine surrogate azidonorleucine (Anl, 2). Other cells are inert to Anl. Right Bacterial cells carrying the NLL synthetase are labeled with a fluorescent alkyne dye (green) in the presence of mammalian macrophages (red). Maraophage proteins are not labeled...

Link AJ, Vink MK, Tirrell DA (2007) Synthesis of the fimctionalizable methionine surrogate azidohomoalanine using Boc-homostaine as precursor. Nat Protoc 2 1884—1887... 

Figure 3. Three of the modules comprising methionine synthase. At the top center is the Bi2- binding fragment [651-896], a structure with two domains, one a four-helix bundle that serves to cap the cofactor, and the other an a/p fold that interacts with the lower face of the corrin macrocycle and binds the nucleotide tail of cobalamin. Measurements of the rates of photolysis of the C0-CH3 bond indicate that the cap domain covers the upper face of the corrin in the substrate-free form of the intact enzyme (7). On the lower right is the activation domain [897-1227] with bound AdoMet. This helmet-shaped single domain is an unusual fold with no resemblance to other well-characterized AdoMet-binding domains (8). On the lower left is the structure of the methyltransferase AcsE from Moorella thermoaceticum, which we take as a surrogate for the folate-binding domain of MetH.

Indirect evidence with synthetic polynucleotides had already suggested that at least two bases—U and A— might be part of the triplet responsible for termination. With most polypeptides used as surrogate messenger, only 10% of the polypeptides synthesized are released however, 60% of the newly made polypeptides are released when the coding polypeptide contains A and U. An important difference between the initiation and termination codon is that initiation requires that an anticodon of tRNA charged with a formyl methionine be lined up, but termination does not require that the codon be coupled with the appropriate anticodon. 

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